Heat transfer and friction characteristics of air flow in microtubes
热能与动力工程专业英语
因此，朗肯循环的热效率 n 是
(1-2).
所需的输出，即除以能量输入 (购买能源)。
Obviously,the thermal efficiency can be improved by increasing the numerator or by decreasing the denominator. This can be done by increasing the pump outlet pressure P2, increasing the boiler outlet temperature T3 or decreasing the turbine outlet pressure P4.
显然，通过增加分子或通过减小分母可以提高热效率。这可以通过增加泵出口压力 P2，锅炉出口温度 T3 的增加或减少涡轮出口压力 P4。
1.1。8 再热循环
很明显与高锅炉压力或低凝汽器压力朗肯循环中运行时很难防止液滴在低压涡轮的部分形成。由于大多数金属不能经受温度约 600 以上，再热周期通常用于防止液体滴形成： 蒸汽涡轮机穿越在一些中间的压力，从而提高 5 中的状态 T 的图图 1-6 的温度加热。然后的蒸汽涡轮低压条经过和进入状态 6 冷凝器。这控制或完全消除了在涡轮中的水分问题。通常，涡轮分为高压涡轮和低压涡轮。再热循环不会显著影响热效率的周期，但它不会导致重大的额外工作输出，表示在图中的地区 4-5-6-4' 的图 1-6-4。再热循环要求额外的设备，在重大的投资和使用这类设备必须是从事经济工作增加的输出的 justifled。如果再热不用于避免液滴形成，凝汽器压力必须相当高，这会导致较低循环效率。在这个意义上，再热显著增大时没有再热，但较高的凝汽器压力相比，周期循环效率。
2020-2021学年牛津版英语七年级下册单词速记学习法(第七组)
单词速记学习法第七组knock怎么读英[nɒk]美[nɑk]是什么意思n.短促的敲打（声）；爆震声；敲击声；敲门（或窗等）声vi.猛烈敲击；与某物相撞；撞到了桌子；vt.（心）怦怦跳；把…撞击成（某种状态）；批评；变形复数：knocks过去式：knocked过去分词：knocked现在分词：knocking第三人称单数：knocks双语释义n.(名词)1.[C]短促的敲打(声) (sound of) a sharp blow2.[C]爆震声 (in an engine) sound of knocking3.[C](板球赛的)一局 (in cricket) innings4.[C]一件倒霉事或麻烦事 a piece of bad luck or troublev.(动词)1.vt. & vi. 敲,击,打 hit or strike2.vt. 批评,数落,非难 say critical or insulting things about sb/sth英英释义knock[ nɔk ]•n.o the sound of knocking (as on a door or in an engine or bearing) "the knocking grew louder"同义词：knockingo negative criticism同义词：roasto a vigorous blow"the sudden knock floored him"同义词：bashbangsmashbelto a bad experience"the school of hard knocks"o the act of hitting vigorously同义词：beltrapwhackwhang•v.o deliver a sharp blow or push :"He knocked the glass clear across the room"同义词：strike hardo rap with the knuckles"knock on the door"o knock against with force or violence同义词：bumpo make light, repeated taps on a surface同义词：taprappinko sound like a car engine that is firing too early同义词：pinkpingo find fault with; express criticism of; point out real or perceived flaws "Don't knock the food--it's free"同义词：criticizecriticisepick apart学习怎么用词汇搭配用作名词(n.)动词+～•get the knock被解雇,遭到失败•hear a knock听到敲门声•receive a knock受到挫折•stand the knock忍受指责•take a knock受到严重损失形容词+～•gentle knock轻轻的敲门声•loud knock重重的敲门声•good knock打一局好球•first knock第一局球•bad knock损失不少钱财•damaging knock破坏性的挫折•hard knock沉重的打击名词+～•engine knock发动机的爆震声用作动词(v.)～+名词•knock a ball拍球•knock colds消除感冒•knock head撞头•knock sb's hometown抨击某人的家乡•knock sb's play抨击某人的戏剧•knock such notions给人以深刻的观念•knock the ash敲烟灰•knock the bottom of the box敲箱子底•knock the dust敲打灰尘•knock the England team挖苦英格兰队•knock the foreign policy抨击外交政策•knock the furniture碰倒家具•knock the glass打破玻璃•knock the nail钉钉子•knock the price降价•knock the wall拆墙•knock the worry摆脱忧愁～+副词•knock badly剧烈撞击•knock loudly发出大声地碰撞•knock about〔around〕流浪•knock down撞倒,拆除,挣(钱)•knock down a machine把机器拆卸开来•knock down a plane击落飞机•knock down an A in history历史考得优等分数•knock down good money挣很多钱•knock down some cash偷一些现金•knock off停止工作,完成,结束,快速写•knock off a few lines匆匆写几句•knock off work歇工•knock out击倒,使昏迷或入睡,彻底击败•knock out the enemy guards干掉敌人哨兵•knock oneself out to get through the difficulty竭尽全力渡过困难•knock oneself out preparing for the experiment努力为实验做好准备•knock oneself out with excessive work过度工作而筋疲力尽•knock over打翻,轻易击败•knock over a lamp打翻一盏灯•knock up击打,草率或匆忙地作出•knock up a meal匆匆做好一餐饭～+介词•knock against偶然碰到•knock at a door敲门•knock into将…击打进或撞进,偶然碰到•knock into the old teacher偶然碰到那位老教师•knock sb off sb's feet把某人打倒在地•knock on the door敲门•knock sb on the head打某人的头•knock sth on the head破坏某事•knock sth to pieces把某物打碎•knock with a bat用球拍打词组短语knock on撞击撞出；敲击（门、窗）knock at敲（门、窗等）knock off击倒；停工；中断knock down击倒；拆卸knock at the door敲门；把……撞倒；撞墙knock out敲空；击倒；打破；使筋疲力竭knock it off停止做；住口，别再讲下去了knock on the door敲门knock over打翻；撞倒knock in（把钉子）钉入knock on wood敲木头，企求好运；吉人天相knock up敲门唤醒；[英口]筋疲力尽；往上敲knock back（摇把）反击，（活塞）逆行，（曲轴）反转；反座；回击，击退；使...大吃一惊knock against撞击，与…冲突；偶然遇见knock sensor爆振传感器；进气流量传感器knock into撞上；与…相撞knock off work敲落工作；歇工更多收起词组短语同近义词辨析knock, beat, strike, hitknock敲门；beat打鼓;连续打；strike敲锣，钟敲几点，猛的一击；hit击中，打一下pat, knock, rap, tap这组词都有“敲、击”的意思，其区别是：pat指用手轻拍以示同情、赞同或爱抚。
建筑环境与设备工程专业英语翻译
A thermodynamic system is a region in space or a quantity of matter bounded by a closed surface. The surroundings include everything external to the system, and the system is separated from the surroundings by the system boundaries. These boundaries can be movable or fixed, real or imaginary.一个热力学系统是一个在空间或有事项的数量由一个封闭的表面范围内的区域。
周围环境包括一切外部系统，系统是从周围环境隔开的系统边界。
这些边界可以是动产或固定的，真实的或想象。
The concepts that operate in any thermodynamic system are entropy and energy. Entropy measures the molecular disorder of a system. The more mixed a system, the greater its entropy; conversely, an orderly or unmixed configuration is one of low entropy. Energy has the capacity for producing an effect and can be categorized into either stored or transient forms as described in the following sections.熵和能量的概念，在任何热力学系统操作。
熵措施分子系统紊乱。
更为复杂的系统，其熵值越大，反之，有序或纯配置是低熵之一。
力学名词中英对照
［推荐］［名词委审定］汉英力学名词（1993）［翻译与翻译辅助工具］［回复］［引用回复］［表格型］［跟帖］［转发到Blog］［关闭］［浏览930次］用户名：westbankBZ反应||Belousov-Zhabotinski reaction, BZ reactionFPU问题||Fermi-Pasta-Ulam problem, FPU problemKBM 方法||KBM method, Krylov-Bogoliubov-Mitropolskii methodKS动态］熵||Kolmogorov-Sinai entropy, KS entropyKdV 方程||KdV equationU 形管||U-tubeWKB 方法||WKB method, Wentzel-Kramers-Brillouin method［彻］体力||body force［单］元||eleme nt［第二类］拉格朗日方程||Lagra nge equati on ［of the seco nd kin d］［叠栅］云纹||moir e fringe;物理学称"叠栅条纹”。
［叠栅］云纹法||moir e method［抗］剪切角||a ngle of shear resista nee［可］变形体||deformable body［钱］币状裂纹||penny-shape crack［映］象||image［圆］筒||cyli nder［圆］柱壳||cylindrical shell［转］轴||shaft［转动］瞬心||instantaneous center ［of rotation］［转动］瞬车由||instantaneous axis ［of rotation］［状］态变量||state variable［状］态空间||state space［自］适应网格||［self-］adaptive meshC 0 连续问题||C0-continuous problemC 1 连续问题||C1-continuous problemCFL条件||Courant-Friedrichs-Lewy condition, CFL conditionHRR场||Hutchinson-Rice-Rosengren fieldJ 积分||J-integralJ 阻力曲线||J-resistance curveKAM定理||Kolgomorov-Arnol'd-Moser theorem, KAM theoremKAM环面||KAM torush收敛||h-c on verge ncep收敛||p-c on verge ncen 定理||Buckingham theorem, pi theorem阿尔曼西应变||Almansis strain阿尔文波||Alfven wave阿基米德原理||Archimedes principle阿诺德舌［头川Arnol'd tongue阿佩尔方程||Appel equation阿特伍德机||Atwood machine埃克曼边界层||Ekman boundary layer埃克曼流||Ekman flow 埃克曼数||Ekman number 埃克特数||Eckert number 埃农吸引子||Henon attractor 艾里应力函数||Airy stress function 鞍点"saddle [point] 鞍结分岔||saddle-node bifurcation 安定[性]理论||shake-down theory 安全寿命||safe life 安全系数||safety factor 安全裕度||safety margin 暗条纹||dark fringe 奥尔-索末菲方程||Orr-Sommerfeld equation 奥辛流||Oseen flow 奥伊洛特模型||Oldroyd model 八面体剪应变||octohedral shear strain 八面体剪应力||octohedral shear stress 八面体剪应力理论||octohedral shear stress theory 巴塞特力||Basset force 白光散斑法||white-light speckle method 摆||pe ndulum 摆振||shimmy 板||plate 板块法||panel method 板元||plate element 半导体应变计||semic on ductor stra in gage 半峰宽度||half-peak width 半解析法||semi-analytical method 半逆解法||semi-inverse method 半频进动||half frequency precession 半向同性张量||hemitropic tensor 半隐格式||semi-implicit scheme 薄壁杆||thin-walled bar 薄壁梁||thin-walled beam 薄壁筒||thin-walled cylinder 薄膜比拟||membrane analogy 薄翼理论||thin-airfoil theory保单调差分格式||monotonicity preserving differenee scheme 保守力||conservative force 保守系||conservative system 爆发||blow up 爆高||height of burst 爆轰||detonation; 又称"爆震”。
热能英语第三版哈工大部分翻译
热能英语第三版哈工大部分翻译Heat transfer involving motion in a fluid caused by the difference in density and the action of gravity is called natural or free convection. Heat transfer coefficients for natural convection are generally much lower than for forced convection ,and it is therefore important not to ignore radiation in calculating the total heat loss or gain. Radiant transfer may be of the same order of magnitude as natural convection, even at room temperatures, since wall temperatures in a room can affect human comfort.传热涉及流体中密度差异和重力的作用引起的流体运动称为自然或自由对流。
自然对流传热系数通常要低于强制对流,因此,重要的是计算总热量损失或增加时不要忽略辐射。
即使在室温条件下，辐射传热可能和自然对流是同一个数量级的,因为在一个房间里壁温度会影响人类生活的舒适度。
Water vapor is one of the products of combustion for all fuels which contain hydrogen. The heat content of a fuel depends on whether this water vapor is allowed to remain in the vapor state or is condensed to liquid. In the bomb calorimeter the products of combustion are cooled to the initial temperature and all of the water vapor formed during combustion is condensed to liquid. This gives the high, or gross, hest content of the fuel with the heat of vaporization included in the reported value. For the low, or net heat of combustion, it is assumed that all products of combustion remain in the gaseous state.水蒸气是所有含有氢的燃料燃烧产物之一。
化工专业英语第三篇翻译
Heat Transfer 传热Heat, as a form of energy, cannot be created or destroyed. Heat can be transferred from one substance to another.热是能量的一种形式,不能创造也不能消灭。
热可以从一个物体传递到另一个物体。
Heat always tends to pass from warmer objects to cooler ones. When a warm substance comes in contact with a cold substance, the molecules of the warm substance collide （碰撞） whth the molecules of the cold substance, giving some of its energy to the cold molecules. This is only one way to transfer heat.热总是倾向于从较热的物体向较冷的物体传递。
当一个暖的物体与一个冷的物体接触时，暖物体的分子与冷物体的分子碰撞，把他们的部分能量传给冷物体的分子。
这仅仅是传递热的一种方式。
In a chemical plant, for example, in a refinery （炼油厂）, transfer of heat is very important , the successful operation of most processes is dependent on correct application of the principles (原理) of heat transfer. Where we are handling （处理；加工；操纵） a hot material, we may insulate（隔离，绝缘） the system to hold the heat in; where the material is cold, we insulate to keep the heat out. Efficient equipment, designed to take full advantage of (充分利用) processing heat, is in use on almost all chemical plants.在化工厂，例如一个精炼厂，传热是非常重要的，大多数过程的成功运行取决于传热原理的正确运用。
abaqus切削热传导公式
abaqus切削热传导公式English Answer:Heat Transfer in Cutting with Abaqus.Heat transfer plays a crucial role in cutting operations, affecting the temperature distribution, tool wear, and workpiece quality. Abaqus offers comprehensive capabilities for modeling heat transfer in cutting simulations, enabling engineers to accurately predict thermal effects and optimize cutting parameters.Heat Transfer Mechanisms in Cutting.During cutting, heat is generated due to friction between the tool and workpiece, plastic deformation of the material, and chip formation. Heat transfer occurs through various mechanisms, including:Convection: Heat transfer between the tool, workpiece,and surrounding environment.Conduction: Heat transfer within the tool, workpiece, and chips.Radiation: Heat transfer through electromagnetic waves.Heat Transfer Modeling in Abaqus.Abaqus provides several methods for modeling heat transfer in cutting simulations:Element-based Heat Transfer: Heat transfer is solved within each element, considering conduction, convection,and radiation.Surface-based Heat Transfer: Heat transfer is applied as boundary conditions on surfaces, such as contactsurfaces between the tool and workpiece.User Subroutines: Custom heat transfer models can be implemented through user subroutines.Governing Equations.The heat transfer analysis in Abaqus is based on the following governing equations:Conservation of Energy: The rate of heat transfer into a control volume minus the rate of heat transfer out of the control volume equals the rate of change of energy within the control volume.Conduction: Fourier's law describes heat conduction as a function of temperature gradient.Convection: Newton's law of cooling describes heat convection as a function of surface temperature and surrounding environment temperature.Radiation: Stefan-Boltzmann law describes heat radiation as a function of surface temperature and emissivity.Material Properties.Accurate material properties are essential for reliable heat transfer simulations. Abaqus requires the following thermal properties:Thermal Conductivity: The ability of a material to conduct heat.Specific Heat Capacity: The amount of heat required to raise the temperature of a unit mass of material by one degree.Density: The mass per unit volume of a material.Boundary Conditions.Appropriate boundary conditions are necessary to define the temperature or heat flux at the simulation boundaries. Common boundary conditions include:Convection Boundary Conditions: Prescribed heattransfer coefficient and reference temperature.Radiation Boundary Conditions: Prescribed surface emissivity and surrounding environment temperature.Temperature Boundary Conditions: Prescribed temperature values on surfaces.Simulation Workflow.The typical workflow for heat transfer modeling in Abaqus involves:1. Defining the geometry and mesh of the model.2. Assigning material properties.3. Applying boundary conditions.4. Specifying heat transfer settings.5. Running the simulation.6. Post-processing the results to analyze temperature distribution, heat flux, and other thermal effects.Benefits of Heat Transfer Modeling in Cutting.Incorporating heat transfer into cutting simulations provides valuable insights into:Temperature Distribution: Predicting the temperature distribution within the tool, workpiece, and chips.Tool Wear: Assessing the impact of heat on tool wear and life expectancy.Workpiece Quality: Evaluating the effects of heat on workpiece surface finish, distortion, and residual stresses.Cutting Parameters Optimization: Identifying optimal cutting parameters to minimize heat generation and improve productivity.中文回答：Abaqus 中切削热传导公式。
Computational Analysis of Enhanced Cooling Performance and Pressure Drop
CONTENTS
9.1 Background Information................................................................................ 250 9.1.1 Introduction........................................................................................ 250 9.1.2 Review of Experimental Evidence..................................................... 251 9.1.3 Review of Computational Analyses................................................... 253 9.1.4 Mixture Viscosity Models.................................................................. 254 9.2 Theory............................................................................................................ 254 9.2.1 Governing Equations......................................................................... 254 9.2.2 Mixture Properties............................................................................. 256 9.2.2.1 Effective Dynamic Viscosity............................................... 256 9.2.2.2 Effective Thermal Conductivity.......................................... 258 9.2.3 Entropy Generation............................................................................ 263 9.2.4 Thermal Performance Comparisons..................................................264 9.2.5 Numerical Method.............................................................................264 9.3 Results and Discussion.................................................................................. 265 9.3.1 Flow Friction Validation Studies....................................................... 265 9.3.2 Convective Heat-Transfer Validation Results....................................266 9.3.3 Friction Factor and Pressure Drop Results........................................266 9.3.4 Convective Heat Transfer................................................................... 269 9.3.5 Entropy Generation............................................................................ 269 9.4 Conclusion..................................................................................................... 271 Acknowledgment.................................................................................................... 273 References............................................................................................................... 273
CO2 传热和摩擦公式 ACRC 教授文章 Heat Transfer and Pressure Drop of Gas Coolers
See discussions, stats, and author profiles for this publication at: https:///publication/279937565Heat Transfer and Pressure Drop of Gas CoolersArticle in ASHRAE Transactions · January 2001CITATIONS 27READS533 authors:XD FangNanjing University of Aeronautics & Astronautics65 PUBLICATIONS 547 CITATIONSSEE PROFILEC.W. BullardUniversity of Illinois, Urbana-Champaign158 PUBLICATIONS 2,577 CITATIONSSEE PROFILEPega HrnjakUniversity of Illinois, Urbana-Champaign and CTS226 PUBLICATIONS 1,704 CITATIONSSEE PROFILEHeat Transfer and Pressure Drop of Gas CoolersXiande Fang, Ph.D. Clark W. Bullard, Ph.D. Predrag. S. Hrnjak, Ph.DMember ASHRAE Member ASHRAEABSTRACTIn CO2transcritical cycle of air conditioning and heat pump systems, the heat exchanger operating at supercritical pressures is called a gas cooler. Refrigerant-side heat transfer and pressure drop in gas coolers are different from single-phase in-tube heat transfer and pressure drop at subcritical pressures. This paper offers a comprehensive survey in single-phase in-tube heat transfer correlations of constant thermophysical property fluids, CO2supercritical heat transfer and friction factor correlations, the calculation of pressure drop in supercritical conditions, and the heat transfer and friction factor correlations on gas cooler air sides. Based on comparisons among in-tube heat transfer and friction factor correlations, some suggestions are made thereafter. INTRODUCTIONCarbon dioxide is considered as a potential alternative refrigerant for car air conditioning and heat pump systems. The capacity and COP of CO2 systems depend on the pressure in the high side, because they operate in a transcritical cycle (Figure 1) under most conditions.The process path of a CO2transcritical cycle, as shown in Figure 1, consists of compression (1’-2), supercritical heat rejection (2-3), adiabatic expansion (3’-4), two-phase heat absorption (4-1), and super heating (1-1’) a nd subcooling (3-3’) if a suction line heat exchanger is used.In the heat rejection of a conventional refrigeration cycle, refrigerant changes from gas state into liquid state in the high-pressure side heat exchanger so that condensing phenomena take place and the heat exchanger is called a condenser. During the supercritical heat rejection (Process 2-3 in Figure 1), refrigerant CO2 keeps gas state without phase changing so that the heat exchanger is called a gas cooler instead of a condenser.A gas cooler falls into one of the two categories: air-cooled, as used in air conditioning systems, and water-cooled, as used in heat pumps. For both air-cooled and water-cooled gas coolers, the heat transfer and pressure loss of the refrigerant side abide by the same law. The water-side heat transfer of the water-cooled gas cooler can be described by conventional models (Schonfeld and Kraus 1997; Rieberer and Halozan 1997) so that it is not described in this paper. The air-side heat transfer of the air-cooled gas cooler has attracted more research interests in recent two decades.Xiande Fang is a visiting professor at the Dept. of Building, Civil and Environmental Engineering, Concordia University, Montreal, Canada. C. W. Bullard is a professor and director and P. S. Hrnjak is a research professor and associate director of the Air Conditioning and Refrigeration Center, Dept. of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, Urbana, USA.THIS PREPRINT IS FOR DISCUSSION PURPOSE ONLY, FOR INCLUSION IN ASHRAE TRANSACTIONS 2001, V. 107, Pt. 1. Not to be reprinted in whole or in part without written permission of the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 1791 Tullie Circle, NE, Atlanta, GA 30329. Opinions, findings, conclusions, or recommendations expressed in this paper are those of author(s) and do not necessarily reflect the views of ASHRAE. Written questions and comments regarding this paper should be received at ASHRAE no later than February 9, 2001.The air-cooled gas cooler is an air-cooled louvered fin heat exchanger, which has the flat tubes with the cross section of several independent ports (Chang and Wang 1997). The louvered fin geometries include triangular-channel, rectangular-channel, and plate-and-tube types.Although no phase change takes place at supercritical pressures, the thermophysical properties of CO 2 change drastically during the process (Figure 2). In these circumstances, the heat transfer coefficient and pressure drop are greatly dependent on both the local mean temperature and the heat flux, where the conventional models could not apply (Pitla et al. 1998). At a given pressure, there is a temperature at which CO 2 specific heat capacity has maximum value (Figure 2). This point is called pseudo-critical point.Many of the recent investigations of CO 2 as an alternative refrigerant have been performed in the cycle performance (Lorentzen and Pettersen 1993; Rieberer and Halozan 1997; McEnaney et al. 1999) and thermophysical properties (Span and Wagner 1996; Vesovic et al. 1990). However, studies in local heat transfer coefficients and pressure drop during the heat rejection are fewer. Literature search shows that only five papers (Krasnoshchekov et al. 1969; Baskov et al. 1977; Petrov and Popov 1985; Petrov and Popov 1988; Fang 1999) address specifically the heat transfer and pressure drop of CO 2 cooled at supercritical pressures.Figure 2 Variation of CO 2 Supercritical Thermophysical Properties with TemperatureSeveral papers related to gas cooler simulation have been published (Schonfeld and Kraus 1997; Rieberer andHalozan 1997; Robinson and Groll 1998; Fang 1999). Using Gnielinski equation (1976), Schonfeld and Kraus (1997) and Rieberer and Halozan (1997) developed their computer programs for water-cooled gas coolers. The heat transfer correlation Robinson and Groll (1998) used is Petukhov-Kirillov (1958) equation. Schonfeld and Kraus compared their model predictions with experimental data. They concluded that the heat transfer from supercritical fluids could not be calculated exactly with classical methods of convective heat transfer because their predictions were remarkably higher than the experimental data. Fang (1999) developed a CO 2-specific heat transfer equation. The predictions of his computer program agree with experiment data.Suction line Heat exchanger30031032033034035036005101520253035404550Temperature [K]P r a n d t l N u m b e rFigure 2b Variation of Prandtl Number with Temperature300310320330340350360050001000015000200002500030000350004000045000Temperature [K]S p e c i f i c h e a tc a p a c i t y [J /k g -K ]Figure 2a The Variation of Specific Heat Capacity with TemperatureIt is the purpose of this paper to offer a comprehensive survey in studies of the heat transfer and pressure drop of gas coolers.PRESSURE DROP IN TUBESPressure Drop EquationThe total pressure drop in a section can be calculated by⎪⎭⎫⎝⎛+=ξρ∆D L f 2G p h 2(1)where hydraulic drag factor f h is (Petrov and Popov 1985)i h f f f += (2)where the inertia factor f i , as in one-dimensional approximation, is expressed asmp p w i t 1c G q 8f ⎥⎥⎦⎤⎢⎢⎣⎡⎪⎭⎫ ⎝⎛∂∂-=ρρ (3)For incompressible fluid flow, f i = 0, Equation (1) is reduced to the commonly used Darcy-Weisbach equation⎪⎭⎫⎝⎛+=ξρ∆D L f2G p 2 (4)Darcy-Weisbach Friction FactorMany equations for the Darcy-Weisbach friction factor have been developed. The Blasius ' equation (5) and Filonenko 's equation (6) are widely used for the turbulent flow in smooth tubes (Zukauskas and Karni 1989).)10(Re Re0.316 f 51/4≤= (5))105Re 101(1.64)- Re (1.82log f 64-2⨯≤≤⨯= (6)The “smooth” here means that the wall roughness elements are so small that their influence does not extend beyond the laminar sublayer.There are other opinions about the applicable Reynolds number range of Blasius ' equation (5) and Filonenko 's equation (6). For example, Incropera and DeWitt (1996) introduced Re ≤ 2⨯104 for Blasius ' equation (5) and 3000 ≤ Re ≤ 5⨯106 for Filonenko 's equation (6).Moody (1944) introduced Colebrook 's equation. Colebrook, in collaboration with White, developed an equation which agrees with two extremes of roughness in transition zone.⎪⎪⎭⎫ ⎝⎛+-=Re f 51.27.3R log 2f 10.5rt 0.5 (7)Since Colebrook 's equation cannot be solved explicitly for f, Althul developed an explicit formula which was modified by Tsal (ASHRAE 1993)⎪⎩⎪⎨⎧<+=≥=⎪⎭⎫ ⎝⎛+=018.0f if f 85.00028.0f 018.0f if f f Re 68R 11.0f ''''25.0rt '(8)Friction factors obtained from Althul 's modified equation are within 1.6% of those obtained by Colebrook 's equation.Churchill (1977) proposed a more complicated equation for all flow regimes and all relative roughness, which agrees with the Moody diagram (Moody 1944)()12/12/31616rt .9012Re 37,530R 27.0/Re 71ln 457.2Re 88f ⎪⎭⎪⎬⎫⎪⎩⎪⎨⎧⎥⎥⎦⎤⎢⎢⎣⎡⎪⎭⎫ ⎝⎛+⎪⎪⎭⎫⎝⎛++⎪⎭⎫ ⎝⎛=- (9)The comparison of Blasius ' equation (5), Filonenko 's equation (6), Althul 's modified equation (8), and Churchill 's equation (9) is shown in Figure 3. It is seen that Blasius ' equation (5) can be valid for Re <1.5⨯105, and Filonenko 's equation (6) can be used within Re > 8⨯103.Althul 's modified equation (8) has apparently lower prediction than Churchill 's equation (9) for large relative roughness conditions. When relative roughness R rt ≤ 0.001, the predictions by Althul 's modified equation (8) and Churchill 's equation (9) differ only slightly. It is better to limit the application of Equation (8) to R rt ≤ 0.001. The analytical results are summarized in Table 1. For the fluid flow varying between transitional and fully developed regimes or a tube with relative roughness not neglected, Churchill 's equation (9) is recommended.Friction Factor of Supercritical CoolingThermophysical property variations in the cooling conditions at supercritical pressures significantly affect the pressure drop characteristics. The absolute value of the inertia drag which is negative in cooling conditions is commensurable with the friction drag. At some circumstances, this can decrease the total hydraulic drag to negative values, thereby resulting in the appearance of zones with pressure increasing along tubes.Petrov and Popov (1985) calculated the friction factor of CO 2 cooled in the supercritical conditions in the range of Re w = 1.4⨯104 – 7.9⨯105 and Re m = 3.1⨯104 – 8⨯105. They obtained an interpolation equation of the friction factorsm w m w w0f f ⎪⎪⎭⎫ ⎝⎛=μμρρ (10a)where f 0w , the friction factor at constant thermophysical properties, is calculated by Equation (6) at tube wall temperature T w , and42.0w G q 023.0s ⎪⎪⎭⎫⎝⎛= (10b)Later in 1988, they calculated the friction factor for cooling of supercritical water in the range of Re w = 2⨯104 – 1.88⨯105 and Re m = 2.3⨯104 – 2.03⨯105, and derived a friction factor equation as follows:m0i 3/1m w4/1m w m 0f f 17.0f f ⎪⎪⎭⎫ ⎝⎛+⎪⎪⎭⎫ ⎝⎛=ρρμμ (11)where f 0m is calculated by Equation (6) at mean fluid temperature T m , and the inertia factor f i is given by Equation (3).They claimed that Equation (11) described their calculated data for water, helium, and carbon dioxide at supercritical pressures with the deviation of no more than ±8% in the boundary conditions of T w = constant and q w = constant.No CO 2 -specific experimental correlations are found for the hydraulic drag factor in the cooling conditions at supercritical pressures.Figure 4 compares hydraulic drag factor calculations, where “CO 2 –specific” means the hydraulic drag factor calculated with Equations (2), (3), and (10), “water -specific” denotes that c alculated with Equations (2), (3), and (11), and “constant thermophysical property” stands for that calculated with Churchill 's equation (9). The predictions of the CO 2 –specific equation is over 10% more than those of the water-specific equation and Churchill 's equation (9) with maximum 27.5%. The conditions of Figure 4 are: D = 0.79 mm, p rin = 100 bar, T rin = 120 ︒C, T ain = 35 ︒C, air face velocity = 2.5 m/s, -130< q w /G < -28 J/kg, 6.7⨯103 < Re w < 1.81⨯104, and 7.8⨯103 < Re m < 1.85⨯104.101010100.010.020.030.040.050.060.070.08Reynolds number, ReF r i c t i o n F a c t o r , fFigure 3 The Comparison of Friction Factor Equations0.00.20.40.60.81.01.2Tube length, L [m]H y d r a u l i c d r a g f a c t o rR e y n o l d s n u m b e r a t T m , R e mFigure 4 Camparison of Hydraulic Drag Factor Calculations0.00.20.40.60.81.01.2-0.0045-0.0040-0.0035-0.0030-0.0025-0.0020-0.0015-0.0010000020I n e r t i a f a c t o r , f iT e m p e r a t u rSince Equation (11) is derived from the calculation of water supercritical cooling, it is better to use Equation (10) as the model of CO 2 cooled in supercritical conditions, with f 0w calculated by Churchill 's equation (9) to extend its applicable range. A summary is given in Table 1.Table 1 Summary of Friction Factor CorrelationsFluids applied EquationSuggested applicable rangeConstantthermophysical propertyBlasius ' equation (5) Re <1.5⨯105, smooth tube Filonenko 's equation (6) Re > 8⨯103, smooth tube Althul 's modified equation (8) Re > 8⨯103, R rt ≤ 0.001 Churchill 's equation (9)*All Re, all R rtSupercritical coolingPetrov-Popov 's equation (10)* CO 2, Re w = 1.4⨯104 – 7.9⨯105 Petrov-Popov 's equation (11)CO 2, H 2O, and He, Re w = 2⨯104 – 1.88⨯105* Recommended conditionallyLocal Pressure Drop in TubesThe in-tube pressure drop consists of frictional and local pressure drops. The former is caused by the shear stress at the inner tube wall, and the latter by the change of flow geometry and direction.Generally, the port diameter of a louvered fin gas cooler tube is small. In this circumstance, the some deformation caused by cutting may exist at the port entrance and exit so that the local pressure drop of the tube is commensurable with or even much larger than the frictional pressure drop along the tube.A variety of local resistance coefficients of the refrigerant side were given by Ide’lchik (1966), based on which Fang (1999) correlated some equations for calculating the local pressure drop at port entrances and exits.HEAT TRANSFER IN TUBESIn-Tube Heat Transfer of Constant Thermophysical Property FluidsMany studies of forced convection heat transfer of constant thermophysical property fluids in turbulent regime have been performed. Dittus –Boelter 's equation and Sieder –Tate 's equation (Incropera and DeWitt 1996) are widely quoted by heat transfer textbooks.Hausen (1959) proposed the following equation:14.0w3/242.04/3)]()L D (1[Pr )180(Re 037.0Nu μμ+-= (12)where fluid dynamic viscosity μw is evaluated at T w , and all other properties are evaluated at T m . The applicablerange was suggested to be in 0.6 < Pr < 103 and 2300< Re <106. However, some researchers (Gnielinski 1976) indicated it should be used only in transitional region.Based on theoretical analyses, Petukhov et al. (1958, 1963, and 1973) proposed following equation for determining the local heat transfer coefficient of fully developed turbulent flow in long tubes:1)(Pr (f/8)A A (f/8)RePrNu 2/31/221-+=(13)where the friction factor f is calculated by Blasius ' equation (5) or Filonenko 's equation (6) according to the Reynolds number, all properties are evaluated at T m , and A 1 and A 2 are shown in Table 2.Table 2 Coefficients A 1 and A 2 in Petukhov 's Equation (13)Authors/Year A 1 A 2 Suggested applicable rangeRe PrPetukhov-Kirillov/1958 1.07 12.7104 - 5⨯1060.5 – 200 Petukhov-Popov/19631+3.4f3/1Pr8.17.11+104 - 5⨯1060.5 – 200Petukhov-Kurganov- Gladuntsov/1973 0.639001.07-+ 12.7 Fully developedturbulent flow* 0.7 - 5⨯105 *The applicable range of the Petukhov-Kurganov-Gladuntsov equation is not clear in their paper. They said it was “for fully developed turbulent flow” at first, and mentioned it “has been checked out experimentally over the ranges of 0.7≤ Pr(Sc) ≤5⨯105 and 4⨯103≤ Re ≤ 6⨯105” later.Gnielinski (1976) studied Hausen 's and Petukhov-Kurganov-Gladuntsov 's equations to obtain an equation valid for both the transitional and the fully developed turbulent regimes. He proposed a modified equation with all properties evaluated at T m :1)(Pr (f/8)7.1211000)Pr -(f/8)(Re Nu 2/31/2-+=(14)Comparing the equation predictions with approximately 800 experimental data in the range of 2300 < Re < 106 and 0.6 < Pr < 105, Gnielinski (1976) concluded that the equation described nearly 90 percent of the experimental data to be within ±20%.The term 14.0w )/(μμin Hausen 's equation (12) is used for considering the influence of large property variations on the heat transfer. Studying the heat transfer of high heat flux densities, Hufschmidt and Burck (1968) proposed a factor 11.0)(w Pr/Pr to modify Petukhov-Kirillov 's equation (13).Gnielinski (1976) adopted 11.0)(w Pr/Pr to modify his equation (14) for liquids, and 45.0w m )/T T ( for gases. For gases, he compared the experimental data of Nusselt number with the results calculated by his equation. They were in good agreement with each other when Nusselt number was greater than 400. However, the average deviation of the calculated results is about +20% of the experimental data when Nusselt number was less than 300.Petukhov et al. (1973) suggested the following equation to modify their equation (13):)log5.153.0(m w 4/1m p w p 3/1m w om m mwT T c c k k Nu Nu μμ+-⎪⎪⎭⎫ ⎝⎛⎪⎪⎭⎫ ⎝⎛⎪⎪⎭⎫⎝⎛= (15)where Nu 0m is calculated with Petukhov-Kurganov-Gladuntsov 's equation (13) at T m . They claimed that most of the experimental data were within ±10% of the model prediction.For Equations (12) - (14), a brief sammary is given in Table 5, and the comparison is shown in Figure 6, which is in the same conditions as those of Figure 4. Petukhov 's equation (13) is recommended for use in the range of 104 ≤ Re ≤ 5⨯106, where the differences in prediction among its three forms are no more than 5.1% when 1< Pr <150. Hausen 's equation (12) has lowest prediction. Gnielinski 's equation (14) is close to Hausen 's equation (12) in the transitional regime (2300 ≤ Re ≤ 104) and to Petukhov 's equation (13) in the range of 104 ≤ Re ≤ 5⨯106. In the range of 106 ≤ Re ≤ 5⨯106, the differences in prediction between Gnielinski 's equation (14) and Petukhov 's equation (13) are no more than 5% when 1< Pr <150.Based on the above comparison, Gnielinski 's equation (14) is recommended for use in the range of 2300 ≤ Re ≤ 5⨯106.conditions because it is much more difficult to obtain experimental data on local heat transfer in cooling conditions.Krasnoshchekov et al. (1969) conducted an experiment at supercritical pressures with CO 2 cooled in a long horizontal tube of an inner diameter = 2.22 mm, and derived the following equation from the experimental data:mw p p nm wow w c c Nu Nu ⎪⎪⎭⎫ ⎝⎛⎪⎪⎭⎫ ⎝⎛=ρρ (16a)where Nu ow is calculated with Petukhov-Kirillov 's equation (13) at T w , m is given bykw p p c c B m ⎪⎪⎭⎫⎝⎛= (16b) and p c is defined aswm wm p T T i i c --=(17)2 They thought this was partly due to extrapolation of n, B, and k.Baskov et al. (1977) conducted an experiment at supercritical pressures with CO 2 ascending flow cooled in a long vertical tube of an inner diameter = 4.12 mm, and found their experimental data were lower than those calculated with Equation (16). They obtained the following equation from their experimental data: 2x 10101010510671010010001000050000R e y n o ld s n u m b e r , R e N u s s e l t n u m b e r , N uIn-Tube Heat Transfer of Supercritical CoolingThe heat transfer in gas cooler tubes occurs at supercritical pressure where the thermophysical properties of the fluid changedrastically. The great variations in the thermophysical properties cause the heat transfer coefficient to be greatly dependent on both the local mean temperature and the heatflux. The variations include two aspects: along and perpendicular to the fluid flow direction. The effect of the former can be eliminated if the dimensional step in calculations is smallenough, but that of the latter can not. The specific characteristics of heat transfer at supercritical pressures have attracted many researchers (Polyakov 1991). However, most of published papers are related to heating conditions because it is much more difficult tonw m mw p p ow w c c Nu Nu ⎪⎪⎭⎫ ⎝⎛⎪⎪⎭⎫⎝⎛=ρρ (18)where Nu ow is calculated with Petukhov-Kurganov-Gladuntsov 's equation (13) at T w , and p c has the same definition as Equation (17); m = 1.4, n=0.15 for T m /T pc ≤1, and given in Table 4 for T m /T pc >1; T pc is the temperature at which the fluid specific heat has maximum value at the given pressure.Table 4 m and n in Baskov-Kuraeva-Protopopov 's EquationParameters wp pc c />1wp pc c /<1 p, bar80 100 120 80 100 120 m 1.2 1.6 1.6 0.45 0.45 0.45 n 0.15 0.10 0 0.15 0.10 0Comparing the predictions of Equation (18) with the experimental data of Krasnoshchekov et al. (1969) and Tanaka et al. (1971), Baskov et al. (1977) found that the calculations were 25% lower than the former on average and most within ± 25% of the latter. They speculated that the divergence might be connected with the difference in the orientation of the tubes and the schemes of the experimental units. However, after the experiments conducted to compare ascending flow with descending flow, they concluded that in their experimental range (0.95⨯105≤ Re m ≤ 6.44⨯105), there was no effect of free convection on heat transfer.Petrov and Popov (1985) proposed the following equation based on their theoretical calculation for CO 2 cooled in the supercritical region with 5m 4108Re 101.3⨯≤≤⨯, 1.4⨯104 ≤ Re w ≤ 7.9⨯105, and -350 ≤ q w /G ≤ -29 J/kg:nw p p w ow w c c G q 001.01Nu Nu ⎪⎪⎭⎫⎝⎛⎪⎭⎫ ⎝⎛-= (19) where⎪⎩⎪⎨⎧>⨯-≤⨯-=--;1c /c when )G /q (1049.0,1c /c when )G /q (10466.0n w w p p w 4p p w 4 (20)and Nu 0w is calculated with Petukhov-Popov 's equation (13) at T w . Petrov and Popov (1985) compared their calculation results by Equation (19) with those by Krasnoshchekov-Kuraeva-Protopopov 's equation (16) and Baskov-Kuraeva-Protopopov 's equation (18), and found that their results were lower than those by Equation (16), and not larger than ±15% of those by Equation (18) in the region of -240 ≤ q w /G ≤ -50 J/kg.Summarizing their calculations for carbon dioxide, water, and helium, Petrov and Popov (1988) obtained a generalized equation for the heat transfer of supercritical cooling⎥⎥⎦⎤⎢⎢⎣⎡⎪⎪⎭⎫ ⎝⎛--⎪⎪⎭⎫ ⎝⎛-+=f f A 1f f A 1Pr 8f 12.71.07Pr Re 8fNu i 2i 1m w 2/3m m ρρ (21)where the inertia factor f i is calculated with Equation (3), the friction factor f is calculated with Equation (11), andmmp k c Pr μ=(22)For CO 2, A 1 = 0.9, A 2 = 1.0, for water, A 1 = 1.1, A 2 = 1.0, and for helium, A 1 = 0.8, A 2 = 0.5.The above literature study shows that in-tube heat transfer under supercritical pressures has its specific characteristics. The literature on cooling conditions is limited and the results differ from each other considerably. Figure 7 shows the comparison of Petukhov 's equation (13), Krasnoshchekov-Kuraeva-Protopopov 's equation (16), Baskov-Kuraeva-Protopopov 's equation (18), and Petrov-Popov 's equations (19) and (21), where Nu ow in the CO 2-specific equations (Equations (16), (18), (19) and (21)) is calculated with Gnielinski 's equation (14). Generally, CO 2-specific Equations (16), (18), (19) and (21) have higher heat transfer predictions than Petukhov 's equation (13) which is used for constant thermophysical property fluids. The more close to the pseudo-critical point the temperature, the greater the variations. The conditions of Figure 7 are the same as those of Figures 4-6. Petukhov 's equation (13) has been proved to be suitable for constant thermophysical property fluids. It is not applicable to CO 2 supercritical cooling because of great thermophysical property variations in the circumstance. The CO 2-specific equations are all based on Petukhov 's equation (13) with the modification to thermophysical property variations. Therefore, if in the range far from CO 2 pseudo-critical point, where variations of CO 2 thermophysical properties with temperature are small enough, the best of the CO 2-specific equations should have the least deviation from Petukhov 's equation (13). Those whose predictions are extremely high or low are excluded. Based on these considerations, Petrov-Popov 's equation (19) is preferred.Based on Gnielinski 's equation (14) and Petrov-Popov 's equation (19), Fang obtained the following in-tube heat transfer model of gas coolers:nw p p w 2/3w 1/2w w w w w c c G q 001.011)(Pr /8)(f 7.12A 1000)Pr -/8)(Re (f Nu ⎪⎪⎭⎫ ⎝⎛⎪⎭⎫ ⎝⎛--+= (23a) where⎪⎩⎪⎨⎧≥<⨯+=-6w 6w w810Re 07.110Re Re 1071A (23b)In Equation (23), f w is the friction factor evaluated at T w by Churchill 's equation (9), and p c , n are calculated by Equations (17) and (20), respectively.0.00.20.40.60.81.01.2Tube length [m]H e a t t r a n s f e r c o e f f i c i e n t [W /m 2-K ]T e m p e r a t u r e [C ]Figure 7 Comparison of CO 2 - Specific Heat Transfer Equations401000004000Figure 8 compares Fang 's equation (23) with Petrov-Popov 's equation (19) in the range of 104< Re w < 106 and –350 < q w /G <- 20 J/kg. The deviation of Equation (23) from Equation (19) is less than 5.5 %. Equation (23) is used as the in-tube heat transfer model to simulate a gas cooler tested in the range of 3500<Re w <2.5⨯104 and -115< q w /G <-3 J/kg (McEnaney et al. 1999; Yin et al. 1998). The predictions agree with the experimental data very well. Fang suggested that his equation (23) could be used in the range of 3000 ≤ Re w ≤ 106 and -350≤ q w /G <0 J/kg.Generally, the in-tube heat transfer of gas coolers varies between transitional and fully developed turbulent regimes so that Fang 's equation (23), with Nu ow evaluated by Gnielinski 's equation (14), is recomended for calculating in-tube heat transfer of CO 2 supercritical cooling. A brief sammary of in-tube heat transfer of CO 2 supercritical cooling is listed in Table 5.Table 5 Summary of In-Tube Heat Transfer CorrelationsFluids applied Equation Suggested applicable rangeConstantthermophysical property Hausen’s equation (12) Re =2300 - 106, Pr =0.6 - 103 Petukhov’s equation (13) Re =104 - 5⨯106, Pr =0.5 - 2000 Gnielinski 's equation (14)* Re =2300 -5⨯106, Pr =0.5 - 2000Supercritical coolingK-K-P 's equation (16) CO 2, Re w = 6⨯104 – 3⨯105 ,Re m = 9⨯104 – 3⨯105B-K-P 's equation (18) CO 2, Re m= 1⨯105 – 6.5⨯105Petrov-Popov 's equation (20) CO 2, Re w = 1.5⨯104 – 8⨯105, Re m = 3⨯104 – 8⨯105, q w /G=-350-(-29)Petrov-Popov 's equation (21) CO 2, H 2O , and He , Re w = 2⨯104 – 1.9⨯105, Re m = 2⨯104 – 2⨯105, q w /G=-800-(-200)Fang’s equation (23)*CO 2, Re w = 3⨯103 –106, q w /G=-350- 0* RecommendedAIR-SIDE HEAT TRANSFER OF LOUVERED FIN GAS COOLERSThe air-side heat transfer coefficient of gas coolers can be determined bySt )Vc (h a p a ρ= (24) where3/2Pr /j St = (25)From experimental data with louvered fin heat exchanger with triangular channels, Davenport (1983) correlated a dimensional model for the Colburn j factor which is dimensionless.4000Re 300F F L L Re 249.0jh pD 26.0l 1.1l l33.0h 42.0L <<⎪⎪⎭⎫ ⎝⎛=- (26)where, Re L p is the Reynolds number based on louver pitch L p , Re D his the Reynolds number based on thehydraulic diameter D h , and all the units of characteristic length are in mm.。
(完整版)建筑环境与设备工程专业英语翻译
A thermodynamic system is a region in space or a quantity of matter bounded by a closed surface. The surroundings include everything external to the system, and the system is separated from the surroundings by the system boundaries. These boundaries can be movable or fixed, real or imaginary.一个热力学系统是一个在空间或有事项的数量由一个封闭的表面范围内的区域。
周围环境包括一切外部系统，系统是从周围环境隔开的系统边界。
这些边界可以是动产或固定的，真实的或想象。
The concepts that operate in any thermodynamic system are entropy and energy. Entropy measures the molecular disorder of a system. The more mixed a system, the greater its entropy; conversely, an orderly or unmixed configuration is one of low entropy. Energy has the capacity for producing an effect and can be categorized into either stored or transient forms as described in the following sections.熵和能量的概念，在任何热力学系统操作。
熵措施分子系统紊乱。
更为复杂的系统，其熵值越大，反之，有序或纯配置是低熵之一。
核专业英语背诵材料2.0
Unit 1Helium---------------------氦uranium------------铀Gaseous state-----------气态的artificially------------人工的The perfect gas law------理想气体定律Boltzmann constant--- 玻尔兹曼常数neutrons --------------中子electrostatic -------静电的，静电学的Specific heat capacity--- 比热容Plank constant---------普朗克常量Fission----------------裂变fusion-----------------聚变Maxwellian distribution--麦克斯韦分布microscopic------------微观的Macroscopic-----------宏观的quantum number-------量子数Laser-----------------激光deuterium--------------氘Tritium----------------氚deuteron---------------氘核Trition----------------氚核atomic mass unit------原子质量单位Avogadro’s number----阿伏伽德罗常数binding energy----------结合能Substance-------------物质internal-----------------内部的Spontaneously --------自发地circular-----------------循环的Electronic ------------电子的neutral-----------------中性的Qualitative -----------定性的dissociation-------------分解分离Disrupt--------------使分裂A complete understanding of the microscopic structure of matter and the exact nature of the forces acting (作用力的准确性质) is yet to be realized. However, excellent models have been developed to predict behavior to an adequate degree of accuracy for most practical purposes. These models are descriptive or mathematical often based on analogy with large-scale process, on experimental data, or on advanced theory.一个完整的理解物质的微观结构和力的确切性质(作用力的准确性质)尚未实现。
不同翅片形式管翅式换热器流动换热性能比较
不同翅片形式管翅式换热器流动换热性能比较摘要：随着制冷空调行业的发展,人们已经把注意力集中在高效、节能节材的紧凑式换热器的开发上,而翅片管式换热器正是制冷、空调领域中所广泛采用的一种换热器形式。
对于它的研究不仅有利于提高换热器的换热效率及其整体性能,而且对改进翅片换热器的设计型式,推出更加节能、节材的紧凑式换热器有着重要的指导意义。
由于翅片管式换热器在翅片结构形式和几何尺寸的不同,造成其换热性能和阻力性能上的极大差异。
本文概述目前国内外空调制冷行业中的普遍采用的几种不同翅片类型（平直翅片、波纹翅片、开缝翅片、百叶窗形翅片）的换热及压降实验关联式及其影响因素，对不同翅片形式的管翅式换热器的换热及压降特性的实验关联式进行总结，并对不同翅片的流动换热性能进行了比较。
正确地选用实验关联式及性能指标，将对翅片管式换热器的优化设计及其制造提供可靠的依据。
关键词：翅片形式；管翅式；换热器；关联式；流动换热性能Study on heat transfer and flow characteristics of fin-and-tube heat exchangers with various fin typesAbstract：With the development of refrigeration and air conditioning, high efficiency, energy saving and material saving compact type of heat exchanger is development, as one kind of compact heat exchanger, fin-and-tube heat exchanger has a wide application in future. It is necessary to develop compact heat exchanger which is more energy saving and material saving to improve the heat exchanger thermal efficiency and the overall performance of heat transfer.This paper summaries the heat transfer and pressure drop correlations of different fin surfaces, and the corresponding influencing factors. The heat transfer and friction characteristic of these kinds of fin types are compared, and the results show the difference of these fin types. The appropriate correlation and evaluation criterion will provide reliable foundation to the design and optimization of compact heat exchangers.Key words：Fin-and-tube heat exchanger; Heat transfer and flow characteristics; Experimental correlations; Comparison目录1 绪论 (2)1.1课题背景及研究意义 (3)1.2管翅式换热器简介 (3)1.3管翅式换热器的特点 (4)1.4 管翅式换热器的换热过程 (4)1.5研究现状 (5)1.5.1国外实验及模拟研究进展 (5)1.5.2国内研究现状和数值模拟 (6)1.5.3管翅式换热器及发展趋势 (8)1.6 管翅式换热器的不同形式的翅片研究现状 (9)2影响翅片换热和压降性能的主要结构因素 (11)2.1翅片间距对换热特性和压降特性的影响 (12)2.2管排数对换热特性和压降特性的影响 (12)2.3管径对换热特性和压降特性的影响 (13)2.4管间距对换热特性和压降特性的影响 (13)3．不同翅片经验关系式总结及比较 (14)3.1 平直翅片经验关系式的总结 (14)3.2 波纹翅片经验关系式的总结 (18)3.3 百叶窗翅片经验关系式的总结 (23)3.4 开缝翅片经验关系式的总结 (26)4．四种翅片经验关系式比较 (31)结论 (38)参考文献 (40)致谢 (44)1绪论1.1课题背景及研究意义换热器是国民生产中的重要设备，其应用遍及动力、冶金、化工、炼油、建筑、机械制造、食品、医药及航空等各工业部门。
热能与动力工程专业英语译文-第一章译文
Through the application of thermodynamic principles, modern heat engines have been developed.We are facing the reality that fossil fuel reserves are diminishing and will be insufficient in the forseeable future.Consequently, to those who study thermodynamics, increasing efficiency in the use of fossil fuels and the development of alternate sources of thermal energy are the real challenges to technology for today and tomorrow.Thermodynamics is a branch of science which deals with energy, its conversion from one form to another, and the movement of energy from one location to another. Thermodynamics is involved with energy exchanges and the associated changes in the properties of the working fluid or substance.Although thermodynamics deals with systems in motion, it does not concern itself with the speed at which such processes or energy exchanges occur.Thermodynamics, like other physical sciences, is based on observation of nature. Engineering thermodynamics consists of several parts, such as basic laws, thermal properties of the working fluids, process and cycle and so on.Energy is a primitive (原始的）property. We postulate（假定）that it is something that all matter has.Kinetic energy and potential energy are two forms of mechanical energy.A change of the total energy is equal to the rate of work done on the system plus the heat transfer to the system.Enthalpy can be used either as an extensive property H or as an intensive property h.The two terms v2/2 and gz represents kinetic energy and potential energy respectively. Although the net heat supplied to a thermodynamic system is equal to the net work done by the system, the gross energy supplied to the system must be greater than the net work done by the system.Not all of the input heat is available for producing output work because some heat must always be rejected by the system.Related to the second law statements are the concepts of availability of energy, entropy, process reversibility and thermal efficiency.In all reversible processes there is no change in the availability of the energy evolved in the process.Due to this concept of availability of energy, the following statements can be made: Only a portion of heat energy may be converted into work.Entropy S is an abstract thermodynamic property of a substance that can be evaluated only by calculation.From the above expression one can find that the value of entropy of the system will increase when the heat is transferred into the system.Processes that return to their initial state are called cyclic processes.The Carnot cycle is most efficient cycle possible operating between two given temperature levels.In the ideal Rankine cycle the efficiency may be increased by the use of a reheater section. The process of reheating in general raises the average temperature at which heat is supplied to the cycle, thus raising the theoretical efficiency.After partial expansion the steam is withdrawn from the turbine and reheated at constant pressure. Then it is returned to the turbine for further expansion to the exhaust pressure. For the portion of the heat-addition process from the subcooled liquid to saturated liquid, the average temperature is much below the temperature of the vaporization and superheating process.From the viewpoint of the second law, the cycle efficiency is greatly reduced.If this relatively low-temperature heat-addition process could be raised, the efficiency of the cycle would more nearly approach that of the Carnot cycle.The refrigeration cycle is used to transfer energy (heat) from a cold chamber, which is at a temperature lower than its surroundings.The basic refrigeration cycle consists of a sequence of processes utilizing a working fluid, called the refrigerant, usually in continuous circulation within a closed system.The refrigerant receives energy in the evaporator (cold chamber) at a temperature below that of the surroundings, and then rejects this energy in the condenser (hot chamber) prior to returning to its initial state.In the absence of friction these mechanical energies are completely interchangeable; that is, one unit of potential energy can be ideally converted into one unit of kinetic energy, and vice versa.It represents energy modes on the microscopic level, such as energy associated with nuclear spin, molecular binding, magnetic-dipole moment, molecular translation, molecular rotation, molecular vibration, and so on.In a static fluid, there is no motion of one layer of fluid relative to an adjacent layer, so there are no viscous shear forces.A knowledge of fluid statics is necessary for the solution of many familiar problems, such as the determination of total water force on a dam, the calculation of pressure variation throughout the atmosphere.With no relative motion between fluid particles, there are no shear forces acting on the element, only normal forces (due to pressure) and the gravity force.In order to solve problems in fluid flow, it is often necessary to determine the variation of pressure with velocity from point to point throughout the flow field.As one knows, a streamline is a continuous line drawn in the direction of the velocity vector at each point in the flow.For one-dimensional flow, the flow properties of which do not vary in the direction normal to the streamline, the constant in the Bernoulli equation is the same for all streamlines. The term pv is called flow work (energy/mass), the term v2/2 is the kinetic energy per unit mass; and gz is the potential energy per unit mass.There are two basic types of flow, each possessing fundamentally different characteristics. The first type is called laminar flow, the second turbulent flow.The transverse movement of a particle of fluid from a faster-moving layer to aslower-moving layer will have the effect of increasing the velocity in the slower-moving layer.The inlet length required to attain fully developed flow is dependent on the type of flow.In an analysis of flow through a pipe, we are interested in the type of flow, whether laminar or turbulent, since the shear stress and resultant frictional forces acting on the fluid vary greatly for the two types.Another way of looking at the difference between laminar and turbulent flows is to consider what happens when a small disturbance is introduced into a flow.The thickness of the laminar sublayer depends on the degree of turbulence of the main stream—the more turbulent the flow, the thinner the sublayer.We know that when a fluid flows through a pipe, the layer of fluid at the wall has zero velocity; layers of fluid at progressively greater distances from the pipe surface have higher velocities, with the maximum velocity occurring at the pipe centerline.However, even though the velocity fluctuations are small, they have a great effect on the flow characteristics.Furthermore, with the large number of random particle fluctuations present in a turbulent flow, there is a tendency toward mixing of the fluid and a more uniform velocity profile. When smoke leaves a cigarette, it travels upward initially in a smooth, regular pattern; at a certain distance above the cigarette, however, the smoke breaks down into an irregular pattern.Even in turbulent pipe flow, with the great majority of the flow characterized by rough, irregular motions, there will always be a thin layer of smooth laminar flow near a wall, for the particle fluctuations die out near a boundary.When the central of core region of the flow disappears, the flow is termed fully developed viscous flow.The science of heat transfer is concerned with the analysis of the rate of heat transfer taking place in a system. Heat flow will take place whenever there is a temperature gradient.Heat conduction is the term applied to the mechanism of internal energy exchange from one body to another, or from one part of a body to another.Heat conduction is realized by the exchange of the kinetic energy of the molecules by direct contact or by the drift of free electrons in the case of heat conduction in metals.The Fourier law may be used to develop an equation describing the distribution of the temperature throughout a heat-conducting solid.The term “steady state conduction” was defined as the condition which prevails when the temperatures of fixed points within a heat-conducting body do not change with time.The te rm “one-dimensional” is applied to a heat conduction problem when only one space coordinate is required to describe the distribution of temperature within a heat-conducting body.The solution of heat conduction problems involves, in general, the writing of the general heat conduction equation in terms of the appropriate number of arbitrary constants and then the evaluating of these constants by use of the imposed boundary conditions.The electrical analogy may be used to solve more complex problems involving both series and parallel thermal resistances.When fluid flows over a solid body or inside a channel while temperatures of the fluid and the solid surface different, heat transfer between the fluid and the solid surface takes place as a consequence of the motion of fluid relative to the surface.The multiplicity of independent variables results from the fact that convection transfer is determined by the boundary layers that develops on the surface.The velocity boundary layer is defined as the thin layer near the wall in which one assumes that viscous effects are important.It should be emphasized that a thermal boundary layer can also be defined as the region between the surface and the point at which the fluid temperature has reached a certain percentage of the fluid temperature.The thermal boundary layer is generally not coincident with the velocity boundary layer, although it is certainly dependent on it.Numerous analytic expressions are available for the prediction of heat transfer coefficient in laminar tube flow.There are numerous important engineering applications in which heat transfer for flow over bodies such as a flat plate, a sphere, a circular tube, or a tube bundle are needed.The temperature variation within the fluid will generate a density gradient which, in a gravitational field, will give rise, in turn, to a convective motion as a result of buoyancy forces.The fluid motion set up as a result of the buoyancy force（浮力）is called free convection, or natural convection.The flow velocity in free convection is much smaller than that encountered in forced convection; therefore, heat transfer by free convection is much smaller than that by forced convection.According to the different condensing situation, condensation can be divided into filmwise condensation and dropwise condensation.The phenomenon of heat transfer in boiling is extremely complicated because of a large number of variables involved and very complex hydrodynamic developments occurring in the process.All bodies continuously emit energy because of their temperature, and the energy thus emitted is called thermal radiation.The radiation energy emitted by a body is transmitted in the space in the form of electromagnetic waves according to Maxwell’s classic electro magnetic wave theory or in the form of discrete photons according to Planck’s hypothesis(假说）.The emission or absorption of radiation energy by a body is a bulk process; that is, radiation originating from the interior of the body is emitted through the surface.Heat exchangers are devices that facilitate heat transfer between two or more fluids at different temperatures.The C.O.P. of a refrigerating machine is ratio of Refrigerating effect to Work input.The C.O.P. of a refrigerator, unlike the efficiency of a heat engine can be much larger than unity.The essential parts of a vapor compression system are Evaporator Compressor condenser, and Expansion valve.There are three types of vapor compressor: reciprocating, rotary, centrifugal.A vapor absorption system uses heat (thermal) energy to produce refrigeration.In an absorption system, the commonly used working substance is a solution of refrigerant and solvent.The four important factors involved in a complete air conditioning installation are:(i) Temperature control, (ii) Humidity control , (iii) Air movement and circulation, (iv) Air filtering, cleaning and purification .Give some applications of refrigerationdomestic refrigerationcommercial refrigerationindustrial refrigerationManufacture and preservation of medicinesPreservation of blood and human tissuesProduction of rocket fuelsComputer functioningmarine and transportation refrigerationWhat is a vapor compression system?A typical Vapor Compression Refrigeration SystemComponentsEvaporator: Heat exchangers for refrigerant to absorb heat from refrigerated space Compressor: to raise the temperature and pressure of refrigerant by compression Condenser: Heat exchangers for refrigerant to reject heat to the environmentReceiver tank: a reservoir to store the liquid refrigerantExpansion valve: or Refrigerant flow control, to reduce refrigerant pressureCycle diagramsWhat is the working principle of a vapor absorption system?Absorption refrigeration cycleA vapor absorption system uses heat (thermal) energy to produce refrigeration.In an absorption system, the commonly used working substance is a solution of refrigerant and solvent, such as Ammonia/water and Water/lithium bromide.A absorption refrigeration system also contains an evaporator and condenser which operate in exactly same way as for vapor compressor cycle.There is a second circuit around which an absorbent or solvent fluid flows. The evaporated refrigerant vapor is absorbed into the solvent at low pressure, and there is a net surfeit of heat for this process.The solvent, now diluted by refrigerant is raised to the high pressure by a liquid pump. High pressure refrigerant vapor is then produced by the addition of heat to the mixture, in the generator.Nuclear energy results from changes in the nucleus of atoms.As a nucleus splits, it releases a tremendous amount of heat.The nucleus splitting process is completely fissioned, it will create as much heat as the burning of 1500 short tons of coal.In 1911 the physicist Ernest Rutherford first discovered the existence of a subatomic particle, later referred to as the nucleus.In 1938, two German chemists, Otto Hahn and Fritz Strassmann reported they had produced the element barium by bombarding(轰击) uranium with neutrons.This reaction had in fact split an uranium nucleus into two nearly equal fragments(碎片）, one of which was a barium（钡）nucleus and another was a krypton（氪）nucleus.Albert Einstein developed his famous relativity theory and related the matter to energy by the equation E=mc2.Cadmium（镉）rods were used to control the chain reaction.By 1960, nuclear power generating systems in the range of 150 to 200 MW were in commercial operation.Free neutron capture upsets the internal force, which holds together the tiny particles called protons and neutrons in the nucleus.Besides the heat energy produced, fission releases an average of two or three neutrons and such nuclear radiation as gamma rays.If one of the neutrons emitted is captured by another fissionable nucleus, a second fission takes place in the manner similar to the first.When the fission becomes self-sustaining, the process is called a chain reaction.Nuclear reactors used for electric power generation consist of four main parts.They are (1) the fuel core, (2) the moderator and coolant, (3) the control rods, and (4) the reactor vessel .The fuel core contains the nuclear fuel and is the part of the reactor in which the fission takes place.In fission process the fertile materials( for instance, the U-238 ) are converted to fissile. Fertile: 可变成裂变物质的The nuclear fuel is generally contained in cylindrical rods surrounded by cladding materials，such as aluminum(铝), magnesium(镁), zirconium(锌), stainless steel, and graphite(石墨). The moderator is the substance used in nuclear reactor to reduce the energy of fast neutrons to thermal neutrons.The reactor coolant is used to remove heat from the reactor fuel core, including light water, heavy water, air, carbon dioxide, helium, sodium(钠), potassium(钾), and some organic liquids.Control rods are long metal rods that contain such elements as boron硼, cadmium镉, or hafnium罕. These elements absorb fast neutrons and therefore help control a chain reaction.The reactor vessel is a tanklike structure that holds the reactor core and other internals. The two principal types are the PWR and BWR. Both reactors use enriched uranium and light water as coolant as well as moderator.The coolant first flows downward through the annular space between the shield wall and the core barrel into a plenum at the bottom of the vessel.Then the coolant reverses its direction and flows upward through the fuel core.The heated coolant is collected at the upper plenum and exits the vessel through outlet nozzles.A reactor coolant system is usually designed with two or more closed coolant loops connected to the PWR, each containing its own steam generator and coolant pump.The steam-water mixture from the tube bundle passes through a steam swirl旋转vane叶片assembly where steam is separated from the water.In addition to the steam generator, each coolant loop in the PWR has its own pump.An electrically heated pressurizer is connected to one of the coolant loops and is used to serve the whole coolant system.The pressurizer is used to maintain the coolant pressure during steady-state operation, and to limit the pressure changes, preventing the pressure from exceeding the design limit. Boiling water nuclear steam supply system mainly consists of reactor vessel and reactor coolant circuits.Unlike the PWR, BWR system does not have the intermediate heat exchanger, or steam generator, between the coolant loop and the feedwater and steam system.For a BWR plant, steam is generated within the nuclear reactor and transferred directly to the steam turbine.A disadvantage of the BWR system is that radioactive carry-over into the steam must be guarded against and special provisions made to reduce leakage at the shaft seals of the turbine.The plant, having a peak capacity of 12 kWe, has been intended as a demonstration and a pilot plant for electricity production from solar energy.The plant is composed of three main parts: a field of flat plate solar water collectors (primary circuit); a hot water storage tank (interface); and a turbo-generator group (secondary circuit).The operating mechanism of the plant is based on the principle of converting solar energy into thermal energy.The converted energy is then stored in the hot water storage tank until reaching a temperature level of 100°C (called the index temperature), which triggers the startup of the turbo-generator group operation.The primary circuit of the plant consists of 396 flat plate solar collectors covering a net aperture area of 760 m2.The converted solar energy into thermal energy is stored in a sensible heat form within a water storage tank.The geometry of the storage tank presents the advantage of favoring the forming of a thermal stratification within the storage.The turbo-generator group (TGG) consists of an evaporator, a turbine, a condenser and an alternator.The evaporator and the condenser are both heat exchangers made of copper tubes allowing the heat transfer between the fluid and both the hot and cold sources.The turbine is of a single stage type characterized by an axial flux having a rotation speed of 900 rpm.A parabolic concentrator unit is designed to increase the temperature at the bottom of the storage tank whenever the climatic conditions are favorable.。
基于多孔黏结层的超疏水复合涂层制备及其耐磨性研究
第52卷第11期表面技术2023年11月SURFACE TECHNOLOGY·63·基于多孔黏结层的超疏水复合涂层制备及其耐磨性研究汪希奎1,2，苏一凡1，程真1，花颢轩1，刘星宇1，王蕊1，周张恒1，侯泽钟1，李卓然1，赵俊豪1，张友法1*（1.东南大学 a.材料科学与工程学院 b.江苏省先进金属材料高技术研究重点实验室，南京 211189；2.贵州大学 机械工程学院，贵阳 550025）摘要：目的提高超疏水涂层的耐磨性。
方法采用底面复合方法增强超疏水涂层的附着性和耐磨性，通过发泡剂在树脂底漆表面形成均匀孔隙结构，使喷涂于底漆表面的部分超疏水纳米颗粒嵌入孔隙中，通过硬化树脂的凸起结构有效保护超疏水纳米颗粒，从而提高涂层整体的耐磨性。
在摩擦磨损试验机上开展橡胶磨损测试，综合评价涂层的耐磨性能，并通过扫描电子显微镜和同轴光学显微镜对涂层表面的原始形貌及磨损形貌进行分析，通过接触角测量仪对涂层磨损前后的表面润湿性进行测试。
结果当异构十六烷的质量分数为50%、预热温度为130 ℃、预热时间为100 s时，在底漆表面可形成较深且分布均匀的孔隙结构，基于该底漆制备的超疏水复合涂层的耐磨性相对更好。
在30 N载荷下，优化涂层经橡胶磨损700次后，仍能保持较好的疏水性。
结论通过发泡剂对底面复合涂层进行改进，可有效提高超疏水纳米涂层与基底之间的黏结强度；底漆表面的孔隙结构有利于超疏水颗粒的嵌入，充分利用硬化树脂的凸起结构对嵌入的超疏水颗粒进行保护，可有效提高底面复合超疏水涂层的整体耐磨性。
关键词：超疏水；纳米涂层；耐磨性；树脂底漆；发泡剂；孔隙结构中图分类号：TB332 文献标识码：A 文章编号：1001-3660(2023)11-0063-09DOI：10.16490/ki.issn.1001-3660.2023.11.005Fabrication and Wear Resistance of Robust SuperhydrophobicComposite Coating Based on Porous Adhesive LayerWANG Xi-kui1,2, SU Yi-fan1, CHENG Zhen1, HUA Hao-xuan1, LIU Xing-yu1, WANG Rui1,ZHOU Zhang-heng1, HOU Ze-zhong1, LI Zhuo-ran1, ZHAO Jun-hao1, ZHANG You-fa1*(1. a. School of Materials Science and Engineering, b. Jiangsu Key Laboratory of Advanced Metallic Materials, SoutheastUniversity, Nanjing 211189, China; 2. School of Mechanical Engineering, Guizhou University, Guiyang 550025, China)ABSTRACT: Superhydrophobic surface is a nanostructured surface that can provide excellent waterproof, dustproof and anti-fouling properties. In the past few years, a surge has been seen in research interest in these surfaces, particularly in收稿日期：2023-07-02；修订日期：2023-10-10Received：2023-07-02；Revised：2023-10-10基金项目：国家自然科学基金（52071076，52205304）；贵州大学自然科学专项（特岗）项目（（2023）25）Fund：National Natural Science Foundation of China (52071076, 52205304); Natural Science Special Program of Guizhou University for Special Post ((2023) 25)引文格式：汪希奎, 苏一凡, 程真, 等. 基于多孔黏结层的超疏水复合涂层制备及其耐磨性研究[J]. 表面技术, 2023, 52(11): 63-71. WANG Xi-kui, SU Yi-fan, CHENG Zhen, et al. Fabrication and Wear Resistance of Robust Superhydrophobic Composite Coating Based on Porous Adhesive Layer[J]. Surface Technology, 2023, 52(11): 63-71.*通信作者（Corresponding author）·64·表面技术 2023年11月areas such as anti-icing, anti-corrosion, antibacterial activity, oil-water separation, heat transfer, and water collection. The potential applications of superhydrophobic coating are broad and diverse, making it one of the important new materials that have emerged in the past 20 years. In all superhydrophobic coating preparation technologies, nano-coating technology is an important means to promote the industrial application of superhydrophobic surfaces because of its convenient construction, convenient mass production and low cost. However, in practical applications, the wear resistance has a great effect on the application range and service life of the coating. Coating with poor wear resistance may be badly worn in a short time, leading to a rapid decline in its superhydrophobic properties. The coating with outstanding wear resistance can provide longer protection and extend the working life of the surface. Therefore, wear resistance should be fully considered in the design and preparation of superhydrophobic coatings. The wear resistance of the coating can be improved by optimizing the coating preparation process, selecting high wear resistance materials, and adding additives. At the same time, for the practical application of superhydrophobic coating, strict wear resistance testing and evaluation are also needed to ensure that it can meet the actual needs.In order to improve the wear resistance of the superhydrophobic coating, the method of combining primer and topcoat was adopted to enhance the coating adhesion and wear resistance. Foaming agent formed a uniform pore structure on the surface of the resin primer, so that some superhydrophobic nanoparticles sprayed on the primer surface were embedded into the pores, and the superhydrophobic nanoparticles were effectively protected by the raised structure of the hardened resin. Then, the overall wear resistance of the coating could be improved. Furthermore, rubber wear test was carried out by the friction and wear testing machine, and the wear resistance of the coating was evaluated comprehensively. The original morphology and wear morphology of the coating were analyzed by scanning electron microscope and coaxial optical microscope, and the surface wettability of the coating before and after wear was tested by contact angle measuring instrument. When the mass proportion of isocetane was 50%, the preheating temperature was 130 ℃and the preheating time was 100 s, the primer surface could form deep and evenly distributed pore structures, and the wear resistance of the superhydrophobic composite coating prepared based on the primer was relatively better. The results indicated that under 30 N of load, the optimized coating could still maintain good hydrophobicity after 700 times of rubber wear. The bonding strength between the superhydrophobic nano-coating and the substrate can be effectively enhanced by improving the composite method with blowing agent. The pore structure on the resin primer surface is conducive to the embedding of superhydrophobic nanoparticles, and the convex structure of the hardened resin can be fully used to protect the embedded superhydrophobic particles, which can effectively improve the overall wear resistance of the composite superhydrophobic coating.KEY WORDS: superhydrophobic; nano-coating; wear resistance; resin primer; foaming agent; pore structure研究表明，基于荷叶效应研发的超疏水表面具有优异的超疏水性，在自清洁、防雾、防冰、抗腐蚀及耐指纹等方面具有较好的应用前景，近十几年来一直受到国内外研究者的普遍关注[1-8]。
传热学专业英语词汇
Chapter 1 Thermodynamics and Heat Transfer 主要内容1.Concepts:heat (thermal energy)、heat transfer、thermodynamics、total amount of heat transfer、heat transfer rate、heat flux、conduction、convection、radiation2.Equations:1) The first law of thermodynamics (conservation of energy principle)2) Heat balance equation: a) closed system; b) open system (steady-flow)3) Fourier’s law of heat conduction4) Newton’s law of cooling5) Stefan-Boltzmann law主要专业词汇heat transfer 传热、热传递、传热学thermodynamics热力学caloric 热素specific heat 比热mass flow rate 质量流率latent heat 潜热sensible heat 显热heat flux热流密度heat transfer rate热流量total amount of heat transfer总热量conduction导热convection对流radiation辐射thermal conductivity 热导率thermal diffusivity 热扩散率convection/combined heat transfer coefficient 对流/综合换热系数emissivity 发射率absorptivity 吸收率simultaneous heat transfer 复合换热Chapter 2 Heat Conduction Equation主要内容1.Concepts:temperature field、temperature gradient、heat generation、initial condition、boundary condition、steady\transient heat transfer、uniform\nonuniform temperature distribution2.Equations:1) Fourier’s law of heat conduction (§2-1)2) Heat conduction equation (inrectangular\cylindrical\spherical coordinates) (§2-2、§2-3)3) Boundary conditions: (§2-4)a)Specified temperature B. C.b) Specified heat flux B. C. [special case(dt/dx=0):insulation、thermal symmetry];c) Convection B.C.d) Radiation B.C.e) Interface B.C.4) Average thermal conductivity k ave(§2-7)5) Solution of one-dimensional, steady heat conduction inplane walls、cylinders and spheres (k =const)：a) no heat generation, specified B.C.: T(x) or T(r) (§2-5)Q(x) or Q(r), Q=constb) with heat generation, Specified B.C. or Convection B.C. : (§2-6)∆T max=T o-T s= gs2/2nk ; q(x)=gx/n; T s=T + gs/nh characteristic length S, shape factor n:plane walls —s = L (half thickness), n = 1cylinders ——s =r o, n = 2spheres ——s =r o, n =33.Methods: Solve a heat transfer problem1) Mathematical formulation (differential equation & B.C.)2) General solution of equation3) Application of B.C.s4) Unique solution of the problem主要专业词汇temperature field\distribution温度场\分布temperature gradient温度梯度heat generation热生成(热源)initial\boundary condition初始\边界条件transient heat transfer瞬态(非稳态)传热isothermal surface 等温面Heat conduction differential equation 导热微分方程trial and error method试算法iterate迭代convergence 收敛Chapter 3 Steady Heat Conduction主要内容1.Concepts:multilayer\composite wall overall heat transfer coefficient Uthermal resistance R t thermal contact resistance R c critical radius of insulation R crfin efficiency fin effectiveness2.Equations:✓Multiplayer plane wall、cylinders and spheres:✓Fin: fin equation——refer to the attachment.1) Uniform cross-section: refer to the attachment.2) Varying cross-section: refer to the attachment.主要专业词汇thermal resistance热阻parallel 并联in series串联thermal contact resistance 接触热阻composite wall 复合壁面thermal grease 热脂cross-section 横截面temperature execess 过余温度hyperbolic 双曲线的exponent 指数fin 肋(翅)片fin base 肋基fin tip 肋端fin efficiency 肋效率fin effectiveness 肋片有效度Chapter 4 Transient Heat Conduction主要内容1.Concepts:lumped system analysis characteristic length (L c=V/A)Biot number (Bi=hL c /k) Fourier number ( τ = at/L)2.Equations:●Bi≤0, lumped system analysis (§4-1)●Bi>0, Heisler/Grober charts OR analytical expressions1-D：a) infinite large plane walls, long cylinders and spheres (§4-2)b) semi-infinite solids (§4-3)multidimensional: product solution (§4-4)主要专业词汇lumped system analysis 集总参数法characteristic length 特征长度（尺寸）dimension 量纲nondimensionalize 无量纲化dimensionless quantity 无量纲量semi-infinite solid 半无限大固体complementary error function 误差余函数series 级数production solution 乘积解Chapter 5 Numerical Methods in Heat Conduction主要内容1.Concepts:control volume (energy balance) method、finite difference method、discretization、node、space step、time step、mesh Biot number、mesh Fourier number、mirror image concept、explicit/implicit method、stability criterion (primary coefficients ≥0)Numerical error: 1) discretization/truncation error; 2) round-off error2.Methods:Numerical solution:1) Discretization in space and time (∆x, ∆t);2) Build all nodes’finite difference formulations (including interior and boundary nodes);i.Finite difference methodii.Energy balance method (i.e.Control Volume method)3) Solution of nodal difference eqs. of heat conduction;i.Direct method: Gaussian Eliminationii.Iterative method: Gauss-Seidel iteration主要专业词汇control volume 控制容积finite difference有限差分Taylor series expression泰勒级数展开式mirror image concept 镜像法Elimination method 消元法direct/iterative method 直接/迭代方法explicit/implicit method 显式/隐式格式stability criterion 稳定性条件primary coefficients 主系数unconditionally 无条件地algebraic eq. 代数方程discretization/truncation error 离散/截断误差round-off error 舍入误差Chapter 6、7 Forced Convection and NaturalConvection主要内容1.Concepts:Nu、Re、Gr、PrForce/natural convection、external/internal flow、velocity/thermal boundary layerflow regimes、laminar/turbulent flowhydrodynamic/thermal entry region、fully developed regionCritical Reynolds Number (Re c)、hydraulic diameter (D h)、film temperature (T f)、bulk mean fluid temperature (T b)logarithmic mean temperature difference ( T ln)volume expansion coefficient (β= 1/T)effective thermal conductivity (K eff = K Nu)2.Equations:Drag force ：F D = C f AρV2/2Heat transfer rate：Q = hA(T s-T )3．Typical Convection Phenomena:1) Forced convection：external flow——flow over flat plates (§6-4)——flow across cylinders and spheres (§6-5)internal flow——flow in tubes (§6-6)2) Natural convection：flow over surfaces (§7-2)flow inside enclosures (§7-3)主要专业词汇Force/natural convection 自然/强制对流laminar/turbulent flow 层/湍流boundary layer 边界层laminar sublayer 层流底层buffer layer 缓冲层transition region 过渡区flow regimes 流态inertia/viscous force 惯性/粘性力shear stress 剪切应力friction/drag coefficient 摩擦/阻力系数friction factor 摩擦因子dynamic/kinematic viscous 动力/运动粘度wake 尾流stagnation point 滞止点flow separation 流体分离vortex 漩涡rotational motion 环流velocity fluctuation 速度脉动hydrodynamic 水动力学的hydraulic diameter 水力直径fully developed region 充分发展段volume flow rate 体积流量arithmetic/logarithmic mean temperature difference 算术/对数平均温差volume expansion coefficient 体积膨胀系数interferometer 干涉仪asymptotic渐近线的effective thermal conductivity 有效热导率analogical method 类比法integral approach 积分近似法order of magnitude analysis 数量级分析法similarity principle 相似原理Chapter 9 Radiation Heat Transfer主要内容1.Concepts:black body、gray body、diffuse surface、emissive power (E)emissivity (ε)、absorptivity (α)、reflectivity (ρ)、transmissivity (τ) irradiation(G)、radiosity(J)、reradiating(adiabatic) surfaceview factor (F ij)、radiation network、space resistance、surface resistance radiation shieldgas radiation、transparent medium to radiation、absorbing and transmitting mediumws:Blackbody：(1) Plank’s law(2) Stefan-Boltzmann’s law(3) Wien’s displacement lawGraybody：(4) Kirchhoff’s lawActual body：E (T) = εE b(T) = εσT4W/m2Gas：(5) Beer’s law3．Calculation:1) View factor：reciprocity/summation/superposition/symmetry Rulecrossed-strings method2) Radiation heat transfer：Radiation networkOpen system：between two surface (e.g. two large parallel plates) Enclosure：2-surface enclosure；3-surface enclosureRadiation shield主要专业词汇thermal radiation热辐射、quantum theory量子理论、index of refraction 折射系数electromagnetic wave/spectrum 电磁波/波谱、ultraviolet (UV) rays紫外线、infrared (IR) rays 红外线absorptivity 吸收率、reflectivity 反射率、transmissivity 透射率、emissivity (ε) 发射率(黑度)、specular/diffuse reflection 镜反射/漫反射irradiation (incident radiation) 投入辐射、radiosity 有效辐射spectral/directional/total emissive power单色/定向/总辐射力fraction of radiation energy 辐射能量份额(辐射比)、blackbody radiation function 黑体辐射函数view factor 辐射角系数、crossed-strings method交叉线法、reciprocity/summation/superposition/symmetry Rule相互/完整/和分/对称性net radiation heat transfer 净辐射热流量radiation network 辐射网络图、space/surface radiation resistance 空间/表面辐射热阻、reradiating surface重辐射面、adiabatic 绝热的radiation shield遮热板transparent medium to radiation辐射透热体、absorbing and transmitting medium吸收-透过性介质Chapter 10 Heat Exchangers主要内容1.Concepts:heat exchanger type---- double-pipe、compact、shell-and-tube、plate-and-frame、regenerative heat exchangerparallel/counter/cross/multipass flowoverall heat transfer coefficient (U) fouling factor (R f)heat capacity rate capacity rationlog mean temperature difference (ΔT lm)heat transfer effectiveness (ε)number of transfer units (NTU)2.Equations:1) heat balance eq.: Q = C h (T h,in - T h,out)=C c(T c,out - T c,in)2) heat transfer eq.: Q = UAΔT lm( LMTD method)or Q = εQ max = εC min (T h,in ？C T c,in) ( ε-NTU method) 3．Methods:1) LMTD Method：select a heat exchangerKnown: C h、C c、3‘T’Predict: 1‘T’、Q、A2) ε-NTU Method：evaluate the performance of a specified heat exchangerKnown: C h、C c、UA、T h,in、T c,inPredict: Q、T h,out、T c,out主要专业词汇double-pipe/compact/shell-and-tube/plate-and-frame/regenerative heat exchanger套管式/紧凑式/壳管式/板式/蓄热（再生）式换热器parallel/counter/cross/multipass flow 顺流/逆流/叉流/多程流area density 面积密度tube/shell pass 管程/壳程static/dynamic type 静/动态型baffle 挡板header 封头nozzle管嘴guide bar 导向杆porthole 孔口gasket 垫圈lateral 侧面的/横向的fouling factor 污垢因子heat capacity rate 水当量heat transfer effectiveness (ε) 传热有效度number of transfer units (NTU) 传热单元数。
六年级物理与生活英语阅读理解25题
六年级物理与生活英语阅读理解25题1<背景文章>In our daily life, there are many simple physical phenomena that we often encounter. One of the most common ones is friction. Friction exists everywhere. For example, when we walk on the road, the friction between our shoes and the ground helps us move forward. Without friction, we would slip and fall easily. Another example is when we write with a pen. The friction between the pen tip and the paper allows the ink to stay on the paper and form words.Gravity is also a very important physical concept in our life. Everything on the earth is affected by gravity. When we drop an object, it will fall to the ground because of gravity. That's why when we build a house, we need to make sure the foundation is strong enough to bear the weight of the whole building under the influence of gravity.Buoyancy is also interesting. When we put an object in water, if the object is lighter than the water it displaces, it will float. For instance, a wooden block will float on the water surface because the buoyant force acting on it is greater than its own weight. These physical phenomena are not only important in scientific research but also have a great influence on our daily life.1. What helps us move forward when we walk according to the article?A. GravityB. FrictionC. BuoyancyD. Air pressure答案：B。
大三热能专外翻译
UNIT11、传热学是一门试图预测热量传递可以发生在有温差存在的两个物体之间的科学3、热力学告诉我们能量的传递以热量的形式传热学不止可以解释热能怎样被传送同样可以预测在某种特殊的情况下产生的热交换率。
实际上热交换率的客观分析指出了传热学和热力学之间的差异。
热力学研究对象是处于平衡状态的系统。
他可能不被用于预测一个系统从一种平衡状态改变到另一种状态所需要的能量的多少，它可能不被用于预测发生在非平衡状态下的系统的热的交换量有多快//传热学通过提供了可以建立能量交换率的附加实验法则来补充热能第一和第二定律。
作为科学中的热力学被用作传热项目基础的实验法则是非常简单的并且很容易扩展各种各样的实际情况当中。
4、作为热力学和传热学在处理问题时所用方式的一个例子。
分析放入一桶水中的一块热刚块的冷却热力学可能被用于来预测最后钢块和水混合物的平衡温度。
热力学不会告诉我们用了多长时间达到平衡条件或是在平衡条件达到之前经过了某时间后的钢块的温度是多少传热学可以用来预测作为时间函数的钢块和水的温度、6、当温度梯度存在于一个物体中时，经验显示能量将会从高温区域传递到低温区域我们说能量是通过导热传递并且单位面积的传递热率育法向温度梯度成正比UNIT21、当流体以不同的温度与一块平板的表面接触且处于静止或运动时据热力学法则规定能量将朝低温区域流动我们说热量被交换走了并且我们把这个过程称为对流换热过程3、温度TW是直接与平板表面接触的温度。
温度T∞是为了确保平板表面温度不产生明显影响而使流体远离平板表面的所在区域温度面积A是与流体接触的表面区域并且我们应该注意A与热流方向垂直。
比例因子h被叫做传热系数（也是单位面积的导热量或对刘欢热量）并且取决于几何不知方向和表面条件（光滑或粗糙）还有流体的物性和速度4、有两种对流换热模型：强制对流换热和自然对流换热，如果一块条能在一个周围没有额外的动因的房子里，空气的流动将经验的被认为是平板附近存在密度梯度的结果，我们称之为自然对流或是无常对流。
高温熔盐在螺旋槽管内流动与传热的数值模拟
f =
0. 316 4 Re0. 25 l ρu2 d in 2
（ 3）
光滑管压降参照式为： Δp = f （ 4）
f— — —流体的阻力系数； l— — —螺旋槽管的传热有效长度，m； d in — — —螺旋槽管内径，m。
图 7 为阻力系数 f 与 Re 的关系曲线。 由图可 知，螺旋槽管内阻力系数 f 均大于光滑管的阻力系 数，且随着 Re 的增大均变小； 光滑管内阻力系数 f 随 Re 增大而减小的趋势 比 螺 旋 槽 管 大。 相 同 Re 下，阻力系数 f 随着槽深的增加而增加，螺旋槽管 1 槽最深， 其阻力系数 f 是光滑管按式 （ 3 ） 计算 值的 2. 24 ～ 2. 64 倍。比较槽深对管内传热 Nu 和阻 力系数 f 的影响可得，传热强化效果越好， 阻力损 失也越大。因此，设计螺旋槽管时要综合考虑强化 传热技术在提高传热效果的同时 ，增加压降和泵功 率方面所要花费的代价。对此可通过优化设计合理 匹配的传热管结构参数，以达到更高的能量传递效 率，使得传热系统的综合性能最优。
2. 2. 2
流阻与雷诺数 Re 的关系
光滑管阻力系数参照式采用经典的柏拉修斯 （ Blasius） 公式［16］，即
2010 年
第 38 卷
第7 期
沈向阳等： 高温熔盐在螺旋槽管内流动与传热的数值模拟 2005 ，38 ： 1518 － 1530. ［ 9］
— 7 —
传热强化效果越好，阻力损失也越大。
2
2. 1
模拟结果分析
螺旋槽管内流动与传热性能 熔盐入口温度为 573 K， 速度为 2 m / s， 螺旋
槽管 1 内的速度分布云图如图 3 所示。
1. 2
数学模型
假定流动为三维稳态流动，热流密度恒定，建 立管内流动与传热通用控制方程 ： + （ ρu ） + （ ρv） + （ ρw ） = Γ eff x y z x ， x + + S Γ eff Γ eff y ， z ， y z — —速度分量 u、v、w 及温度 T； — — —变量 的有效扩散系数； Γ ， eff — S — — —变量 的源项； u— — —X 方向速度分量，m / s； v— — —Y 方向速度分量，m / s； w— — —Z 方向速度分量，m / s。 同时 μ eff = μ t + μ，其中 μ eff 为分子有效粘度，μ t 为紊流粘度，μ 为层流粘度。控制方程包括连续性 方程、动量方程及能量方程 1. 3 边界条件 管壁为固壁无滑移条件， 壁面为等热流密度， 即 u = 0 ，v = 0 ，w = 0 ，q = q w ； 进口边界条件为 u in = u0 ，v in = 0 ，w in = 0 。 三元熔盐是质量分数为 53% 的 KNO3 、 质量分 数为 40% 的 NaNO2 和质量分数为 7% 的 NaNO3 混 合熔盐 。熔盐进口温度为 300 ℃ （ 573 K ） 时， 定压 比 热 容 为 1 510 J / （ kg · K ） ； 导 热 系 数 为
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Heat transfer and friction characteristics of air flow in microtubesChien-Yuh Yang a ,⇑,Chia-Wei Chen a ,Ting-Yu Lin b ,Satish G.Kandlikar ba National Central University,Jhong-Li,Taoyuan,Taiwan bRochester Institute of Technology,Rochester,NY,USAa r t i c l e i n f o Article history:Received 6May 2011Received in revised form 6September 2011Accepted 6September 2011Available online 29September 2011Keywords:Microtube Heat transferLiquid Crystal Thermographya b s t r a c tSeveral researches dealing with the single-phase forced convection heat transfer inside microchannels have been published in the past decades.The performance of liquid flow has been proved that agrees with the conventional correlations very well.However,owing to the low heat transfer coefficient of gas-eous flow,it is more difficult to eliminate the effects of thermal shunt and heat loss than water flow while measuring its heat transfer performance.None of the heat transfer performance experimental results have been published in the literature.This study provides an experimental investigation on the pressure drop and heat transfer performance of air flow through microtubes with inside diameter of 86,308and 920l m.The Liquid Crystal Thermography method was used to measure the tube surface temperature for avoiding the thermocouple wire thermal shunt effect.The experimental results show that the frictional coefficient of gas flow in microtube is the same as that in the conventional larger tubes if the effect of gaseous flow compressibility was well taken consideration.The conventional heat transfer correlation for laminar and turbulent flow can be well applied for predicting the fully developed gaseous flow heat transfer performance in microtubes.There is no significant size effect for air flow in tubes within this diameter range.Ó2011Elsevier Inc.All rights reserved.1.IntroductionOwing to the fabrication technology development during the past decades,the so-called microtubes with internal diameters smaller than 1mm can be easily made and used for increasing the compactness of heat exchangers.These kinds of heat exchang-ers are able to attain extremely high heat transfer surface area per unit volume,high heat transfer coefficient and low thermal resis-tance.However,the conventional forced convection heat transfer correlations were derived from tubes with diameter much larger than those used in microchannels.They have not been verified to work well for predicting the heat transfer coefficient for flow inside small diameter tubes.The study on heat transfer performance in microchannels has become more important due to the rapid growth of the application for high heat flux electronic devices cooling.Several researches dealing with the single-phase friction and forced convection heat transfer in microtubes have been published in the past years.Wu and Little [1,2]measured the flow friction and heat transfer characteristics of gases flowing through trape-zoid silicon and glass microchannels of hydraulic diameters from 45to 165l m.They observed that the friction coefficients for sili-con channels are in agreement with that for smooth tubes shown in the Moody chart but the results for glass channels are not.They concluded that for microchannels,the relative surface roughness is high for so-called smooth channels.The methods of manufacture and shape of the channels are all factors which affect the value of the friction coefficient in small channels.Choi et al.[3]measured the friction factors and convective heat transfer coefficients for flow of nitrogen gas in microtubes with in-side diameters ranged from 3to 81l m in both laminar and turbu-lent flow regime.The experimental results indicated significant departures from the thermofluid correlations used for conventional sized tubes.They concluded that the Colburn analogy was not applied for microtubes having inside diameters less than 80l m.Yu et al.[4]studied the fluid flow and heat transfer characteristics of nitrogen gas and water in circular tubes with diameters of 19,52and 102l m and Reynolds numbers ranging from 250to near 20,000.The measured friction factors were slightly lower than the Moody chart values for both laminar and turbulent regimes.How-ever,the Nusselt numbers for cooling of water in the turbulent regime were considerably higher than those would be predicted for larger tubes,suggesting that the Reynolds analogy does not hold for micro-channel flow.Adams et al.[5]investigated turbulent sin-gle-phase forced convection of water in circular microchannels with diameters of 0.76and 1.09mm.Their data suggested that the extent of enhancement increases as the channel diameter de-creases and Reynolds number increases.Based on the data they obtained,along with earlier data for small circular channels by0894-1777/$-see front matter Ó2011Elsevier Inc.All rights reserved.doi:10.1016/j.expthermflusci.2011.09.003Corresponding author.Tel.:+88634267347;fax:+88634254501.E-mail address:cyyang@.tw (C.-Y.Yang).Yu et al.[4],they developed a correlation for the Nusselt number for turbulent,single-phase,forced convection in circular microchan-nels with diameters range from0.102mm to1.09mm.Mala and Li[6]investigated waterflow through microtubes with diameters ranging from50to254l m.The experimental results indicate that at high Reynolds number laminarflow condition,the friction factor is higher than that given by the conventional Poiseu-illeflow theory.Celata et al.[7]reported the results of refrigerant R-114flowing in capillary tubes with a diameter of130l m.They found that the friction factor was in good agreement with the Poiseuille theory for Reynolds number below600but higher than that for higher Reynolds number.Li et al.[8]tested the frictional characteristic of waterflowing in glass,silicon and stainless steel microtubes with diameters ranging from79.9to205.3l m.They concluded that for smooth tubes,the friction factor is consistent with the results in macro tubes,while the value of f Re d in rough tubes is15–37%higher than64.Yang et al.[9]provided a system-atic test of friction characteristic for air,water,and liquid refriger-ant R-134a in10tubes with inside diameters from0.173to 4.01mm including the laminar and turbulentflow regime.The test results show that the conventional correlations for large tubes may be adequately used to estimate the friction factors for water,refrig-erant,and laminar airflow in microtubes.For turbulent airflow, however,the friction coefficients are lower than the values pre-dicted by Blasius equation.The discrepancy increased with increas-ing Reynolds number.Yen et al.[10]measured heat transfer performance of laminar refrigerant R-123flow in0.3mm diameter tube by direct attaching K-type thermocouple on the tube wall.The results are in reasonable agreement with the analytical laminar constant heatflux value (Nu d=4.36).However,the Nusselt number data have a very high scattering distribution from around2–5.Lelea et al.[11]investi-gated developing and laminar distilled waterflow in microtubes with diameter0.1,0.3and0.5mm.The experimental results con-firm that,including the entrance effects,the conventional or classi-cal theories are applicable for waterflow through microtubes of the sizes tested.Grohmann[12]measured the heat transfer coefficient of liquid argon at around120K in microchannels with diameter250 and500l m.The results revealed that there is no physical differ-ence in heat transfer mechanisms between macrotubes and micro-tubes.The enhancement of heat transfer coefficients in small tubes compared to conventional correlations was explained with the increased influence of surface roughness.Lin and Yang[13]proposed a non-contacted Liquid Crystal Ther-mography(LCT)method to measure the surface temperature of microtubes.It is successfully avoid the thermal shunt and contact problem caused by using thermocouple.Yang and Lin[14]used this method to measure the heat transfer performance of waterflow in microtubes with inside diameters from123to962l m.The test re-sults showed that the conventional heat transfer correlations for laminar and turbulentflow can be well applied for predicting the fully developed heat transfer performance in microtubes.The tran-sition from laminar to turbulentflow occurs at Reynolds number from2300to3000.This is also the same range as that for conven-tional tubes.There is no significant size effect for waterflow in tubes within this diameter range.Celata et al.[15]presented the work deals with the compress-ibleflow of nitrogen gas inside microtubes ranging from30to 500l m and with different values of the surface roughness(<1%), for differentflow regimes.Their results showed that classic corre-lations can predict friction factor in laminarflow without revealing any evident influence of the surface roughness.The laminar–turbulent transition starts for Reynolds number not lower than 2000for smooth pipes.In the fully developed turbulent regime, an agreement between experimental data and the Blasius correla-tion has been verified for smooth pipes.In summarizing the above literature review,we mayfind that most of the early studies showed significant discrepancy between the experimental results and convention correlations prediction val-ues.However,in the recent years,the friction factors test results for both liquid and gas in microtubes can be adequately predicted by the conventional correlations.The heat transfer test results for liquid can also be well predicted by the traditional forced convection heat transfer correlations.But owing to the measurement difficulties, none of the heat transfer test results for gasflow in microtubes have been published in the literature.The conventional heat transfer correlations have not been verified to be applied forflow in micro-tubes.This study provides an experimental investigation on laminar and turbulent forced convective heat transfer characteristics of air flow in microtubes.The LCT method proposed by Lin and Yang [13]was used in this study to measure the surface temperature of microtubes.2.Experimental method2.1.Tubes size measurement and experiment system setupThree steel tubes with inside diameter of920.1,308.4and 85.6l m were tested in the present study.The tubes inner diameters were measured from the enlarged photographs taken by scanning electron microscope(SEM)for tube with inner diameter of85.6NomenclatureA heat transfer area(m2)c p specific heat(J/kg K)d i tube inside diameter(m)d o tube outside diameter(m)D h hydraulic diameter(m)f friction coefficient,dimensionlessG mass velocity(kg/m2s)h heat transfer coefficient(W/m2°C)k f water conductivity(W/m°C)L tube lengthL h tube heating length(m)L m wall temperature measuring position(m) LCT Liquid Crystal Thermography_m massflow rate(kg/s)Nu d Nusselt number,dimensionless p pressure(Pa)q heat transfer rate(W)q00heatflux(W/m2)R specific gas constant(J/kg K)R a average roughness(m)Re d reynolds number,dimensionlessT temperature(°C)T i inlet water temperature(°C)T x local water temperature(°C)T wx local tube inside wall temperature(°C) TLC thermochromic liquid crystalx axial position of tubes(m)l viscosity(N/m2s)q density(kg/m3)D p pressure drop(Pa)C.-Y.Yang et al./Experimental Thermal and Fluid Science37(2012)12–1813and308.4l m,and optical microscope(OM)for tube with inner diameter of920.1l m.Fig.1shows the sample enlarged photo-graphs of the cross-section view of the tubes.For reducing the mea-surement uncertainties,seven tubes were bundled together,cut and ground to have smooth cross section surface.Each tube diameter was measured and all values were averaged to obtain the average tube diameter.The tubes inside surface roughness were measured by atomic force microscope(AFM)for85.6l m tube and by surface texture measuring instrument for308.4l m and920.1l m tubes. Table1gives the detail dimensions and surface roughness of these tubes.The Detail drawing of the corresponding tube dimensions is shown in Fig.2.The schematic diagram of the test facilities is shown in Fig.3. High pressure airflows from a storage tank through a regulator DC voltage and current were measured by connecting an ampere and a volt meter to the electrodes directly.The power input was calculated by the product of measured current and voltage.Tube surface temperature was measured by the LCT method that proposed by Lin and Yang[13]for avoiding the thermocouple wire thermal shunt effect and will be described in the next section. The heating length and temperature measuring positions are shown in Fig.2for each tube and there values are also listed in Ta-ble1.The measuring position was designed to be longer than the maximum theoretical laminarflow entrance length.But because of the experimental space limitation,the length for920l m tube is slightly shorter than its theoretical entrance length.The experi-mental apparatus and derived parameters uncertainties are listed in Table2.Since the heat transfer coefficient of gaseousflow is low,the heat loss by natural convection from outside of the test section may be important in the heat transfer measurement.For minimiz-ing the heat loss,the test section was enclosed in a vacuum cham-ber.The chamber was evacuated by a vacuum pump before test to maintain the inside pressure below13mTorr.The heat loss was calibrated for each tube before its heat transfer performance test. The test tube was heated inside the vacuum chamber without workingfluid through it.It was maintained at the temperature that same as it was expected for the heat transfer performance test by adjusting the power input.The power input thus can be treated as the heat loss that would be resulted in the heat transfer perfor-mance test.2.2.LCT temperature measurementsThe LCT method that proposed by Lin and Yang[13]was used in this study to measure the surface temperature of microtubes.For920 µm 308 µm86 µmFig.1.Enlarged photographs of the microtubes.Table1Detail dimensions and surface roughness of the tubes tested.Tube notation Tube length,L(mm)Average outsidediameter,d o(l m)Average insidediameter,d i(l m)Standarddeviation(l m)Surfaceroughness,R a(l m)Heating length,L h(mm)Temperature measuringposition,L m(mm)920181.51260920.1 3.020.70478.1428.6 308179.3550308.4 2.740.68582.6719.5 8696.327085.6 1.280.13532.559.2Fig.2.Detail drawing of the test tube.14 C.-Y.Yang et al./Experimental Thermal and Fluid Science37(2012)12–18increasing the accuracy of temperature measurement,two thermo-chromic liquid crystals (TLCs)with 5°C band width from 28–33°C and 38–43°C were used.The diameters of the encapsulated TLCs are from 5to 15microns.The TLCs was painted on the tested sur-face with thickness of approximately 30l m.A black paint was also painted under the TLCs as the background for improving the color resolution by absorbing un-reflected light.The relation between the hue value and temperature was cali-brated in a constant temperature box.Electrical heating wires were attached on inside surfaces of the box to maintain the entire box space at the designated temperatures.Seven T-type thermocouples were evenly placed near the test tube in the box to measure its temperature distribution.The Liquid Crystal Thermograph and temperature measured by thermocouples were recorded simulta-neously.The temperature uniformity in the constant box at differ-ent temperature can be maintained within ±0.2°C.The detail process and uncertainty of the LCT temperature measurement was described in Lin and Yang [13].The standard deviation for the calibrated temperature-hue curve was evaluated within ±0.5°C.2.3.Data reductionThe heat transfer rate q ,was measured from the DC power input deducted by the corresponding heat loss calibrated.It equals to the increased enthalpy of air flow.Since the electrical power was added uniformly on the tube surface,the local air temperature,T x ,at the position x from the heating entrance can be estimated by:q xL h¼_mc p ðT x ÀT i Þð1Þwhere _mis the air flow rate,L h is the tube heating length and T i is the air inlet temperature.From the Newton’s Law of cooling,q 00¼q¼h ðT wx ÀT x Þð2ÞThe local heat transfer coefficient h can be derived as:h ¼qA ðT wx ÀT x Þð3Þwhere A is the heat transfer area,A =p d i L h ,d i is the tube inside diameter.T wx is the local inside tube surface temperature that can be derived from the LCT measured outside surface temperature by the method of one-dimensional heat conduction analysis.The tem-perature difference between the inside and the outside wall was calculated as less than 0.03°C which is among the experimental uncertainty range.The Reynolds number and Nusselt number are defined as the following:Re d ¼Gd iland Nu d ¼hd i k fð4Þwhere G is the air mass flux,G ¼_m=A c ,A c is the tube cross-section area.Since the tubes are small,the tube wall thickness is comparable with the inside diameter,the heat conduction in the wall along axis direction may be important.This axial conduction was estimated by the method of Maranzana et al.[16].The results show that the ratio of axial conduction to the tube inside convection is less than 0.02for all tubes and thus can be neglected.3.Results and discussions 3.1.Friction coefficientsThe total flow pressure drop,D p t was measured at the condition of no heating power added.The frictional pressure drop D p f was evaluated by deducted the inlet (D p i ),exit (D p e )and acceleration (D p a )terms from the measured total pressure drop (D p t ).D p f ¼D p t ÀD p i ÀD p e ÀD p að5ÞD p i ,D p e and D p a were calculated by following those suggested by Kays and London [16]:D p i ¼G 22q i ð1Àr 2þK c Þð6ÞD p e ¼ÀG 22q eð1Àr 2ÀK e Þð7ÞD p a ¼G 2q iq iq oÀ1ð8Þwhere G is the air mass velocity,r is the test section connectors’contraction ratio and K c and K e are the entrance and exit loss coef-ficients which can also be obtained from Kays and London [17].Since the Kn numbers range in the present study,2.8Â10À5to 2.28Â10À6,is far below the slip-continuum flow boundary (10À3)that suggested by Beskok and Karniadakis [18],continuum flow condition was considered in the present study.The friction coeffi-cients can be derived directly from the Darcy’s equation listedbelow.Fig.3.Schematic diagrams of the test facilities.Table 2Uncertainties of the experimental apparatus and derived parameters.ApparatusUncertainties Calibration rangeRTD (°C)±0.10–100T type thermocouple (°C)±0.20–100Differential pressure transducers±0.075%0–10kPa,0–500kPa and 0–9MPa Pressure transducer ±0.4%0–2MPaMass flow meter ±0.6%0–100SCCM,0–5SLM,0–50SLM T wx (LCT)(°C)0.528–43Derived parameters 86l m 308l m 920l m Friction coefficient (f )(%) 2.0–8.00.9–6.10.8–10.0Nusselt number (Nu d )(%)7.3–27.0 6.4–26.5 6.0–14.4Reynolds number (Re d )(%)0.7–4.00.3–3.00.3–4.8f¼D pf2qGd ið9ÞFig.4shows the variation of friction coefficients versus Reynolds number for each tube.It clearly shows that the laminar to turbulent transition Reynolds number is around of2200for all tubes.This is the same as that for conventional larger tubes.In laminarflow re-gime,the friction coefficients can be well predicted by Poiseuille theory(f=16/Re d).In turbulentflow regime,the friction coeffi-cients for920l m tube still agree well with those predicted by the Blasius equation.However,for308l m tube,the friction factor departed from the Blasius prediction values while Reynolds higher than10,000.The discrepancy increases with increasing Reynolds number.For the smallest tube,86l m,the friction factors are signif-icantly lower than those predicted by Blasius equation.These results are the same as those tested by Yang et al.[9].Since the pressure drop was tested under no heating condition, and the viscous shear heating was much lower than the possible heat loss by natural convection from outside of the tube for long tubes with L)d i,theflow can be considered as on the isothermal condition.Shapiro[19]proposed a theoretical equation for calcu-lating friction coefficient that includes the effect offlow compress-ibility as:f¼D h4Lp2iÀp2oG RTÀ2lnpipoð10ÞThe friction coefficients evaluated by the above equation are shown in Fig.5.It shows that the friction coefficients in turbulent flow regime for all tubes agree reasonably with those predicted by the Blasius equation.The above comparison shows that the accel-eration(D p a)terms from Kays and London[17](Eq.(8))over esti-mated the effect of momentum change for a large pressure variationflow condition.The frictional coefficient of gasflow in microtube is the same as that in the conventional larger tubes if the compressibility effect is evaluated by the method that pro-posed by Shapiro[19].3.2.Effect of heat lossSince the heat transfer coefficient of airflow is low,the heat loss by natural convection from outside of the test tube may not be ne-glected in the heat transfer measurement.The ratio of heat loss to the input heating power at variousflow rates for each tube has been measured and shown in Fig.6.The ratios varied from0.76% to46.6%depending on the airflow rate and the tube size.From the fundamentals of convective heat transfer,the in-tube forced convection heat transfer coefficient increases with increasing Rey-nolds number but with decreasing tube diameter.The outside nat-ural convection heat transfer coefficient is almost independent of tube diameter.Therefore,the heat loss ratio is smaller for smaller tube and decreases with increasing Reynolds number as that shown in Fig.6.3.3.Heat transfer coefficientsThe heat transfer rate was measured from the DC power input deducted by the corresponding heat loss calibrated.The derived Nusselt numbers for each tube at various Reynolds number are16 C.-Y.Yang et al./Experimental Thermal and Fluid Science37(2012)12–18shown in Fig.7.Morini et al.[20]suggested that forflow in micro-channels,the low values of the inner diameter limit the signifi-cance of the Grashof number(which depends on the third power of the inner diameter)and,hence,of mixed convection.Gnielinski, [21]proposed a series of correlations for the prediction of the Nus-selt number for pure forced convection.The prediction values by Gnielinski[21]and the original Gnielinski correlation[22]for con-ventional sized tubes were also plotted in Fig.7for comparison. The result shows that in the turbulent regime,the conventional Gnielinski[22]correlation is able to well predict the present test results for the920l m tube.However,for the86l m tube,the Gnielinski[21]correlation for pure force convection provides a better prediction.This agrees with that suggested by Morini et al.[20].For theflow in laminar regime,Nusselt numbers agree well with the theoretical constant heatflux value,4.36.For Reynolds numbers greater than1000,the heat transfer coefficients increase with increasing Reynolds numbers.This shows that the tubes length is not long enough for fully developedflow at high Reynolds number conditions and theflow is still in the developing regime. The thermal entrance length is longer than that estimated by the correlation from Incropera et al.[23].This is in agreement with those tested by Yang and Lin[14]for waterflow.The above test results show that the conventional heat transfer correlation for large tubes can be well applied for predicting the heat transfer performance of airflow in microtubes in both laminar and turbulentflow regime.Furthermore,if we combine the test results by Yang and Lin[14]for waterflow,we may conclude that the conventional heat transfer correlation can be well applied for predicting the heat transfer performance of both air and waterflow in microtubes ranged from86to920l m.There is no significant size effect for airflow in tubes within this diameter range.4.ConclusionsThis study provides an experimental investigation on the pres-sure drop and heat transfer performance of airflow through micro-tubes with inside diameter of86–920l m.The experimental results show that the frictional coefficient of gasflow in microtube is the same as that in the conventional larger tubes if the effect of gaseousflow compressibility that proposed by Shapiro[19]was taken consideration.The conventional heat transfer correlation for laminar and turbulentflow can be well applied for predicting the fully developed airflow heat transfer performance in micro-tubes.If we combine the present results and the results by Yang and Lin[14]for waterflow,we may conclude that the conventional friction and heat transfer correlations can be well applied for both gas and liquidflow in microtubes ranged from86to920l m.There is no significant size effect for airflow in tubes within this diameter range.Furthermore,since the heat transfer coefficient of gaseousflow is low,the heat loss by natural convection from outside of the test tube is not negligible in the heat transfer measurement.The heat loss percentage is smaller for smaller tube and decreases with increasing Reynolds number.AcknowledgmentThe study wasfinancially supported by the National Science Council under Grant No.NSC98-2221-E-008-088-MY3. 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