化工原理英文教材传热传递Heat Transfer

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Lesson03

Lesson 3 Heat Transfer
Li Qiong College of Architecture Engineering North China Institute of Science and technology
Version: 2013-2014
Content

3.1 Heat transfer process（传热过程）
Lesson 3

Heat Transfer
Newton’s law of cooling Consider a surface at temperature ts in contact with a fluid at t∞ (Figure 1B). Newton’s law of cooling expresses the rate of heat transfer from the surface of area As as

Lesson 3
Heat Transfer
2. Thermal Convection
This form of heat transfer involves energy transfer by fluid
movement and molecular conduction.
Lesson 3

Lesson 3

Heat Transfer
4. Dimensionless number commonly used in heat transfer
Nusselt number Reynolds number Prandtl number Stanton number Grashof number Fourier number Peclet number

Chapter 15-11Heat-Exchange Equipment 天大化工原理上册英文版课件

31
Effectiveness of the heat exchanger(传热效率) ε
actual heat transfer rate
maximum possible heat transfer rate
Maximum possible heat transfer rate
Qmax (mcpc )min (Tha Tca )
hi for the tube-side fluid
Nu
hi D k
0.023 Re0.8
Pr1/ 3
v
St
Pr 2 / 3
1 v
0.023 Re0.2
(12.34) (12.34)
ho for the shell-side flow change of flow in direction, cross-area,
recommended
ho Do k
0.287
DoG
0.61
cp
k
0.33
Fa
（15.8）
Typical values of Fa are given in Table 15.1(p443).
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9. Design of heat exchanger
• Classification of exchanger problems • (1)Design : • Given: mh, Tha,Thb (or Tca, Tcb) , and design AT,
13
4. 2-4 Exchanger
• FIGURE 15.4 A 2-4 exchanger.
14
5. Temperature patterns in multipass

chapter- 7 Heat transfer

Heat transfer by conduction
Fourier’s First Law of Heat Transfer
q dT = −k A dx
q is the rate of heat flow, A is the area through which heat is transferred. The expression q/A, the rate of heat transfer per unit areas, is called the heat flux. The derivative dT/dx is the temperature gradient. K is thermal conductivity.
Conduction: Heat will be transferred between adjacent molecules. Convection: Heat is transferred when molecules move from one point to another and exchanges energy with another molecule in the other location. Radiation: the phenomenon of heat transfer by electromagnetic waves.
If the wall of the cylinder consists of layers having different thermal conductivities. T1 and T2 must transect a layer bounded by r1 and r2, which has a uniform thermal conductivity k1. Similarly, the layer bounded by r and r where the temperatures are T and T must also have a uniform thermal conductivity, k2.

清华大学化工原理25第五章传热

第五章传热Key Words: Heat transfer, Conduction, Convection, Rediation, Fourier Law第一节概述化工过程中经常遇到气一液，液－液，气－固，液－固的换热过程加热冷却过程强化保温――削弱过程一、传热的基本方式：热传导分子振动无质点位移对流传热流体质点相对移动强制对流、自然对流电磁波形式传播热辐射放热→辐射能→吸收无需中间介质、能量转换，T 高时的主要方式传热方式相互依存，并不独立存在二、冷热流体接触方式：直接接触式间壁式蓄热式三、传热速率：（传热速率）热流量Q ：J/s热流密度（热通量） q=dQ/ds J/m 2s 四、稳态传热和不稳态传热Q 、q 、及有关物理量（进出口T ， t ）不随时间变化稳态 sQ qds =⎰q ：不随变化（沿管长变化）不稳定：夹套加热T Q Qd θθ=⎰第二节热传导一、温度场和温度梯度：在θ时刻物体（或空间）各点温度分布 t = f (x,y,z,) 若与θ无关→稳定温度场相同t 连结组成等温面等温面不相交等温面上无热量传递温度梯度：0lim n t t n n∆→∂∆=∂∆ n ：法线方向二、Fourier 定律t dQ dsnλ∂=-∂ (与牛顿粘性定律相似) λ：导热系数，负号：热流方向是温度降方向。

三、导热系数λ与物质组成、结构、温度、密度、压强等有关。

单位：/w mK金属 101～102T建材 10-1～100w/mK T绝缘材料 10-2～10-1液体 10-1T (水、甘油除外)气体 10-2～10-1固体：=o (1+KT) λ0：0℃导热系数，金属K<0，非金属K>0 液体：T λ(水、甘油除外)气体：T λ。

高于2000atm ，低于20mmHg ，p λ四、平壁稳定热传导：一平板，长宽与厚比无限大。

dt const Q sdxλλ==- 积分：()121212/s t t t t t t Q bb s Rλλ---===温度分布 11Qx q t t t x s λλ=-=- 直线o o a t λλλ'=+()()()()2212121212122(1)()12o o o o m a s Q t t t t b t t S sa t t a t t tb bλλλλ'⎡⎤=-+-⎢⎥⎣⎦+''=+-=+-多层：n 层不同，b 不同存在n 个温度差（接触面良好） Q 相同（通过各层）()()()31212233412314312123isssQ t t t t t t b b b t t t Q b b b R s s sλλλλλλ=-=-=--∆==++∑由总温差和i，求Q ，由21~i i n QR t t t -=∆，求五、圆筒壁的稳定热传导2s rL π=、Q 相同、q 不同()12122122ln(/)L t t dt dtt t Q s rL Q dr dr r r Rπλλπλ--=-=-==21212m m b r r r rR s Lr s λλπλ--=== 2121ln(/)m r r r r r -= 对数平均值当r 2 / r 1<2时，可用算术平均值计算，误差小于4％多层： ()23141433122412311223312111ln ln ln m m m L t t t t Q b r b b r r s s s r r r πλλλλλλ--==++++ 六、具有内热源的热传导：半径为r o 、长度为L 圆柱体（径向传热）单位时间单位体积产生热'q '2'22dt q rL r Lq dt rdr drλππλ-=∴=-若r ＝r o 时，t ＝t w2'2'2'2maxmax 124014w o tro w t r o o ww w o q r q r dt rdrt t r q r t t r r t t t t r λλλ⎡⎤⎛⎫⎢⎥=-=+- ⎪⎢⎥⎝⎭⎣⎦⎛⎫-==+∴=- ⎪-⎝⎭⎰⎰时温度沿半径方向呈抛物线分布。

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。

传热原理说明英文作文

传热原理说明英文作文Heat transfer is the movement of heat from one object to another due to a difference in temperature. This can occur through three main processes: conduction, convection, and radiation.Conduction is the transfer of heat through direct contact between particles of a substance. When one end of a metal rod is heated, the particles at that end gain kinetic energy and vibrate, colliding with neighboring particles and transferring the heat energy along the rod.Convection is the transfer of heat through the movement of fluids, such as liquids and gases. When a fluid is heated, it becomes less dense and rises, while cooler, denser fluid sinks. This creates a cycle of motion that transfers heat throughout the fluid.Radiation is the transfer of heat through electromagnetic waves. Unlike conduction and convection,radiation does not require a medium to transfer heat. Instead, heat energy is emitted in the form of infrared radiation and can travel through a vacuum, such as space.In everyday life, heat transfer plays a crucial role in various processes, such as cooking, heating and cooling systems, and even the Earth's climate. Understanding the principles of heat transfer allows us to design more efficient technologies and better manage energy resources.。

传热英文讲义-热对流 heat transfer-convection

ConvectionAs mentioned earlier, there are threemechanisms of heat transfer:conduction, convection, and radiation.Conduction and convection are similar inthat both mechanisms require materialmedium, but the difference is thatconvection requires the presence offluid motion. And heat transfer througha liquid or gas can be by convection orconduction, depending on if there ispresence of bulk fluid motion. In otherwords, if there exists bulk fluid motion,it is convection; if there is none, then itis conduction.Convection is complicated because itinvolves fluid motion and heatconduction. Thus, rate of heat transferby convection is higher than conduction.And the higher the fluid velocity, thehigher the heat transfer rate.Further reading about convection is available atAlthough, convection is complex, the rate of convection heat transfer is observed to be proportional to the temperature difference and can be conveniently expressed by Newton’s law of cooling asq conv=ℎ(T s−T∞) (W/m2) (x.1)orQ conv=ℎA s(T s−T∞) (W)(x.2)Whereh = convection heat transfer coefficient, W/m2·o CA s = heat transfer surface area, m2Ts = temperature of the surface, ˚CT∞= temperature of the fluid sufficiently far from the surface, ˚CConvection heat transfer coefficient h can be defined as the rate of heat transfer between a solid surface and a fluid per surface area per unit temperature difference. The convection coefficient is decided by variables influencing convection such assurface geometry, the nature of fluid motion, the properties of the fluid, and the bulk fluid velocity.Typical values of h are given in Table x.1.Table x.1Nusselt NumberIn convection studies, to nondimensionalise the governing equations, dimensionless numbers are introduced to reduce the number of total variables. Nusselt number, viewed as the dimensionless convection heat transfer coefficient is defined as:Nu=ℎL c kWhere k is the thermal conductivity of the fluid and Lc is the characteristic length. The physical significance means the heat transfer ratio of convection to conduction. For Nu=1, the heat transfer is pure conduction.Fluid flowsHeat transfer between moving fluid and solid surface or between moving fluid and interface (to/from air to falling drop).It is commonly assumed that all resistance to heat/momentum transfer occurs in boundary layer defined as part of fluid adjacent to the surface where velocity/temperature changes. Outside boundary layer velocity/temperature is constant.(a)Velocity boundary layerThe fluid flow is characterised by two regions:- Thin fluid layer (boundary layer) in which velocity gradients and shear stresses are large- Free stream (region outside boundary layer) where velocity gradients and stresses are negligible(b) Thermal (temperature) boundary layer- Thin fluid layer of fluid in which temperature gradients are large-exists only when there is a difference between surface temperature and bulk temperature Thickness of boundary layer δt is the value of y for which: Ts−TTs−T∞=0.99If the temperature distribution in boundary layer is known local heat flux from/to the surface can be calcul ated from Fourier’s law in the fluid (there is no fluid motion on the surface)q s′′=−k f∙ðTðy y=0 and q′′=ℎ∙(T s−T∞)In such case convective heat transfer coefficient can also be calculated (no need for experimental data or Buckingham theorem).Local heat transfer coefficientIntegrating local heat transfer coefficient over the entire surface the average value can be calculated:This method of calculation of heat flux to or from the surface is used in CFD packages (numerical solution of momentum and energy balance). In engineering calculations fully developed flows are usually considered therefore average heat transfer coefficients are commonly used (but not always).Structures of boundary layers, local/average heat transfer coefficients1.External flow(a). Flow parallel to flat plateLaminar part:-Local convective heat transfer coefficient:-average heat transfer coefficient ( integrate above from 0 to x):Turbulent part:-Local heat transfer coefficient:-Mixed boundary layer conditions (part of the plate laminar, part turbulent):(b). Flow around cylinderLocal heat transfer coefficient:Average:m and n are constants that can be found from literature.(c). Flow around sphere (similar to flow around cylinder)Internal flow:The extent of boundary layer can be estimated from Re numberD –Tube diameter [m], μ - dynamic viscosity [Pa s], m& - mass flow rate [kg/s],u m - mean fluid velocity [m/s]Thermal entrance regions:(a). Laminar flow:(b). Turbulent flow:Nu number for different types of flow:Fully developed laminar flow:(a). Constant temperature at the wall Nu D=3.66(b). constant heat flux at the wall Nu D=4.36Laminar flow including entry region:Fully developed turbulent flow (properties at T m)(a). Chilton-Colburn equation:(b). Dittus-Boelter equation:(c). Sieder-Tate equation:For noncircular tubes-hydraulic diameter D h=4A c/P, A c– flow crosssectionalarea, P –wetted perimeter (both in Re and Nu numbers)SummaryYou should:A) know/understand that convective heat transfer coefficients depends on:1. Type of flow: internal or external2. Geometry: flat plate, around cylinder/sphere, inside the pipe, etc3. Flow regime - Re number,B) be able to select appropriate correlation (from literature) for given flowconditions,C) be able to distinguish between local or average heat transfer coefficient.。

过控专业英语unit13

术语：gradient; motion;solid;electron;random motion;
• 对流
• 当宏观的流体颗粒流动穿过某特定的表面，比如某一控制体积的边界，它会带来定量的热焓。像这种热焓的流动被称为热对流或者简单对流。由于对流是一种宏观现象，因此只有当力作用在微团或者液流上且该力能够克服摩擦力并维持其运动时，这种传递现象才能发生。对流域流体力学联系紧密。实际上，从热动力学上看，对流不被看成是热量流动，而是被看成热焓的通量。实际上，很难将对流和纯传导截然分开，因此，将二者概括起来称为对流时，热对流的识别就很方便了。对流的例子，比方靠湍流漩涡引起的热焓的传递或者由温暖的空气流过并离开普通换热器引起的热焓的传递。术语：enthalpy;the force of friction;turbulent flow; 短语：not…but;
•自然对流和强制对流 •用于产生流体中对流流动的力有两种。如果流动是由密度差引起的浮力导致的，而且这种密度差是由流体微团的温度梯度引起的，那么这种流动称为自然对流。空气通过散热器的流动就是自然对流的一个例子。如果热流是由机械区分的作用（比如泵或者搅拌器）引起的，流动是与密度梯度相独立的，那么称这种对流为强制对流。热量流动到通过一个加热了的管子泵送而来的流体上就是强制对流的一个例子。在同一流体中，两种类型的力可能同时都很活跃，因此自然对流和强制对流是同时发生的。术语：natrual convection; forced convection;buoyancy force; density; pump; agitator;
Unit 13 Principles of Heat Transfer
Unit 13 热量传递原理

Heat transfer

Lesson 6第 6 课Heat Transfer热量传递Practically事实上、几乎all the operations that are carried out by the chemical engineer involve the production放出or absorption of energy in the form of heat'.1、事实上几乎所有由化学工程师所实施的操作都涉及到以热量形式的能量放出或吸收。

The laws governing the transfer of heat and the types of apparatus设备that for their main object目标the control of heat flow are therefore因此of great importance.2、因此，控制热量传递的相关定律和对于主要目标的热量流动的控制的设备种类就非常的重要When two objects at different temperatures are brought into thermal热的contact接触, heat flows from the object at the higher temperature to that at the lower temperature.3、当两个温度不同的物体相互接触时，热量会从高温物体流向低温物体。

The net flow净流动is -always in the direction方向of the temperature decrease减小2.4、净热流总是沿着温度降低的方向。

The mechanisms原理、机理by which the heat may flow are three: conduction, convection, and radiation.5、根据热量流动的机理不同将其分为三类：热传导、热对流和热辐射。

Unit Four Heat Transfer_石油化工专业英语

4. The rate at which heat flows depends on the amount of temperature difference as well as on the properties of the material through which it has to flow.
radiation n. 辐射 absorption n. 吸收 convert v. （可）转变为，(into)变换，兑换 alter v. 改变 immerse v. 沉浸 coaxial a. 同心的 encounter v. 遇到 concentrically ad. 同心地，同轴地 parallel a. 平行的，并行的，同一方向（目的）的 cylindrical n.圆柱形的 constrain v. 约束，限制，抑制 zig-zag n. 之字形，Z字形
句中两个 “which” 都引导了定语从句，介词前置。译文：热量流动的速率取决于温度差的大小以及要通过热量的物料的性质5. Βιβλιοθήκη isturbance n. 干扰，扰动
disturb v. 打扰，扰乱，妨害 disturb the peace 扰乱治安
6. by means of 依靠，凭借，通过
9. In radiation, thermal energy is transformed into radiant energy, similar in nature to light.
“in nature” 实际上，本质上译文：辐射时，热能变为与光的性质相类似的辐射能。
10. Very commonly in a chemical process, the temperature of a stream of fluid must be altered.

化工原理英文教材传热原理Principles of heat flow in fluids

化工原理 Principles of Chemical Industry
Principles of heat flow in fluids
Typical heat-exchange equipment
Single-pass shell-and-tube condenser
Expansion joint
It is clear from Fig.11-4 that Δt can vary considerably from point to point along the tube, and, therefore, the flux also varies with tube length.
The local flux dq/dA is related to the local value of Δt by the equation
because, as inspection of Figs11-4a and b will show, it is
not possible with this method of flow to bring the exit temperature of one fluid nearly to the entrance temperature of the other and the heat that can be transferred is less than that possible in countercurrent flow.
The temperatures plotted Fig11-4 are average stream temperatures.
The temperature so defined is called the average or mixing-cup stream temperature.

工程热力学与传热学(英文) 第8章热量传递的基本方式

Whenever there is a temperature difference in a medium or between media, heat transfer must occur.
Basic Modes of Heat Transfer（热量传递的基本方式） Conduction（热传导） Convection（热对流） Radiation（热辐射）
Condensation of water vapor on the outer surface of a cold water pipe
8-3 Radiation（热辐射）
8-3-1 Some definitions（热辐射的有关概念）
1. 辐射：是指物体受某种因素的激发而向外发射
辐射能的现象。
（水桶内灼热钢棒的冷却过程）
Thermodynamics
• To predict the final equilibrium temperature of the steel bar-
water combination.（钢棒和水这一体系最终的平衡温度）
• To predict the energy transferred during the process.
8-2 Convection Heat Transfer（热对流）
8-2-1 热对流和对流换热
1. Convection（对流）是指流体各部分之间发生相对位移时，冷热流体相互
掺混所引起的热量传递现象。
2. Convection heat transfer（对流换热）
流体流过另一个物体表面时，流动方向 u∞
t
A
d
t
t A
w1
t
w2

化工原理名词翻译期末整理

第一章流体流动fluid flow动量传递momentum transfer 热量传递heat transfer质量传递mass transfer连续介质continuum流体动力学fluid dynamics流体静力学fluid static粘度viscosity粘性力viscous force动力粘度dynamics viscosity运动粘度kinematic viscosity牛顿型流体newtonian fluid非牛顿型流体non - newtonian fluid塑性流体plastics fluid假塑性流体pseudo - plastics fluid涨塑性流体ditatant fluid非稳态unstable state稳态stable state定态steady state非定态unsteady state连续过程continuous process 间歇过程batch process半连续过程semi-continuous process质量流量mass flow质量流速mass velocity体积流量volumetric flow机械能方程mechanical energy equation柏努利方程Bernoulli equation雷诺实验Reynolds experiment流型flow pattern层流（滞流）streamline flow湍流turbulent flow边界层boundary layer层流底层laminar sub-layer摩擦损失friction loss动压头kinetic head静压头static head速度分布velocity distribution粗糙度roughness压降pressure drop阻力损失drag loss突然缩小sudden contraction突然扩大sudden expansion缩脉（流颈）vena contract管件pipe fitting 弯头elbow三通T-piece截止阀（球心阀）globe value闸阀gate value 哈根-泊谡叶方程Hagen-poiseuille equation 液柱压力计manometer文丘里管Venturi tube文丘里流量计Venturi meter孔板流量计orifice meter转子流量计rotameter流量系数discharge coefficient 气缚airbound特性曲线characteristic curve扬程height，head，lift 扬量capacity汽蚀cavitation汽蚀余量net positive suction head，NPSH第四章传热heat transfer热传导heat conduction热对流heat convection自然对流natural convection强制对流forced convection辐射radiation传热速率heat transfer rate热流量heat flow热通量heat flux总传热系数overall heat transfer coefficient传热膜系数film heat transfer coefficient并流co-current flow逆流countercurrent flow换热heat exchange换热器heat exchanger管壳换热器shell—and—tube heat exchanger套管换热器double—pipe heat exchanger板式换热器plate heat exchanger第五章吸收absorption物理吸收physical absorption化学吸收chemical absorption吸收等温线absorption isotherm吸收速率absorption rate溶解度solubility溶液solution溶质solute溶剂solvent解吸desorption，stripping吸附adsorption变压吸附pressure swing adsorption （PSA）脱附desorption非等温吸收non-isothermal absorption吸收因子absorption factor气液传质设备gas—liquid mass transfer equipment填料塔packed co1umn板式塔tray column气液相平衡gas liquid equilibrium第六章液体精馏连续蒸馏continuous distillation 间歇蒸馏batch distillation精馏rectification馏出液distillate残液residue再沸器reboiler冷凝器condenser道尔顿定律Dalton’s 1aw相对挥发度relative volatility平衡蒸馏equilibrium distillation提馏stripping塔板plate，tray理论级theoretical stage 理论[塔]板theoretical plate实际[塔]板actual plate分凝器partial condenser 操作线operating line回流比reflux ratio全回流total reflux最小回流比minimum reflux ratio 芬斯克方程Fenske’s equation二元混合物binary mixture多元混合物multicomponent mixture精馏段rectification section提馏段stripping section馏出液distillate残液residue回收率recovery。

化工传热英文讲义-换热器（heatexchangers）

化工传热英文讲义-换热器（heatexchangers）Heat exchangers1.Classification:(a). According to flow arrangement(1). Parallel flow (co-current flow)(2). Counter flow (counter-current flow)(3). Cross flow(b). According to type of construction(1). Finned (mainly for gas/liquid systems), un-finned(2). Shell and tube (probably most commonly used), very flexible,relatively cheap, used athigh pressure(3). Plate heat exchangers (when cleaning is important, foodindustry, milk processing),only at low pressure(4). Spiral heat exchangers(5). Compact heat exchangersTypes of heat exchangers(1). Concentric tube heat exchanger(a)Parallel flow, (b) counter-flow. This kind of heat exchanger has low heat transfer rateand thus very limited applications.(2). Shell and tube heat exchangers-very common in liquid-liquid systems, also as condensers.One shell pass and one tube pass (cross-counterflow)One shell pass and two tube passesTwo shell passes and four tube passesCross flow heat exchangers:(a) (b)(a)Finned with both fluids unmixed, (b) un-finned with one fluid mixed and the other unmixed Compact heat exchanger(a) Fin-tube (flat tubes, continuous plate fins), (b) Fin-tube (circulartubes, continuous plate fins), (c) Fin-tube (circular tubes, circular fins),(d) plate-fin (single pass), (e) plate-fin (single pas).Large specific surface area > 700 m2 /m3 but laminar flow because ofsmall size of channels (low heat transfer coefficients).Overall heat transfer coefficient:Where:R f′′-fouling factor (additional thermal resistance)R w-thermal resistance in the wall separating hot and cold fluid (corresponding to conduction) depends on material and geometryηo-overall surface efficiency de fined q=ηo?A(T b?T∞)Typical values of fouling factor:Typical values of overall heat transfer coefficientsEnergy balance (for all types of heat exchangers)Heat load –net change of internal energy in hot and cold fluid:Subscript h – hot fluid, subscript c – cold fluidIf no phase change and specific heat is constant:Energy transfer from hot to cold fluid:In general T h and T c vary along heat transfer surface.In engineering applications the driving force for the heat transfer is expressed in terms of inlet and outlet temperatures and:F- correction factor for non-parallel flowsEnergy balance:This form of energy balance is always used in engineering calculations and designing of heat exchagersCalculations based on log mean temperature differenceParallel flowCounter flowSpecial operating conditionsTemperature distribution depends on thermal capacity of hot C?=m??c p,? and cold C?=m??c p,c fluid.During boiling/ condensation of a single component fluid/ vapour the temperature is constant assuming.For equal thermal capacities of both fluid local temperature difference is constant.Multi-pass and cross flow heat exchangersThe flow conditions can be more complex but the equations developedfor parallel flow heat exchangers can still be used but log meantemperature difference has to be modified:Calculate the driving force for counter current flow and multiply bycorrection factor F (depends on inlet and outlet temperatures and flowpattern) taken from the literature/graphs.Correction factor for two shells and four passes heat exchanger.Correction factor for cross flow heat exchanger with both fluids unmixed.Calculations based on effectiveness –NTU (number of transfer units) methodIf all inlet and outlet temperatures are given the Log MeanTemperature Difference method is recommended, but if only inlettemperatures are given (typical design problem) use of LMTD requiresiterative procedure.In such cases effectiveness-NTU method is better.Effectiveness of heat exchanger is defined as the ratio of actual heattransfer rate to the maximum possible heat transfer rate:Heat transfer rate can be easily calculated if ε, T h,i and T c,i are known as the actual heat transfer rate can be calculated from:Specific relations between NTU and ε depend on the type of heatexchanger and are given in the literature:For concentric tube, counterflow heat exchanger:For other types of heat exchangers algebraic relation are more complex and graphs are commonly used.Effectiveness of single pass, cross-flow heat exchanger with both fluidsun-mixed.SummaryA. The nature of the whole process for which heat exchanger is designedfrequently determines its type:a) hygiene/cleanliness is important (food industry) –plate heat exchanger,b) When process is carried out at high pressure – shell and tube,c) When space is limited – compact heat exchanger,d) Cost is also a major factor, shell and tube exchangers are cheap, plateor compact exchangers are expensive.B. If the inlet and outlet temperatures and mass flow rate of fluid (A) andthe inlet temperature of fluid (B) are known LMTD is recommended.1. Calculate heat load from energy balance for fluid (A)2. Assume flow rate and inlet temperature of fluid (B) and calculateoutlet temperature of fluid (B), or assume outlet temperature of fluid (B)(often temperature constrains) and calculate flow rate from energybalance for fluids (A) and (B).3. Draw the temperature distributions and calculate driving force4. Calculate heat transfer coefficients5. Calculate overall heat transfer coefficient (see methodology above)6. Calculate the heat transfer areaC. Alternatively (if not all temperatures are given) effectiveness-NTUmethod can be used.。

化工原理英文教材传热设备heat-exchange equipment

Special heat-transfer devices used to liquefy vapors by removing their latent heats are called condensers.
Condensers fall into two classes. In the first, called shelland-tube condenser, the condensing vapor and coolant are separated by a tube wall.
Flash p342
2-4 exchanger
The 1-2 exchanger has an important limitation. Because of the parallel-flow pass, the exchanger is unable to bring the exit temperature of one fluid very near to the entrance temperature of the other.
An even number of tube-side passes are used in multipass exchangers. The shell side may be either single-pass or multipass.
In multipass exchangers, floating heads are frequently used.
Flash p339
In an exchanger the shell-side and tube-side heattransfer coefficients are of comparable importance, and both must be large if a satisfactory overall coefficient is to be attained.

化工原理英文教材-传热无相变传热Heat transfer to fluids without phase change

A recognized empirical correlation, for long tubes with sharp-edged entrances, is the Dittus-Boelter equation
Nu hid 0.023Re0.8 Prn k
Where n is 0.4 when the fluid is being heated and 0.3 when it is being cooled.
A better relationship for turbulent flow is known as the Sieder-Tate equation
Nu 0.023 Re0.8 P(r112/-33(2) )0.14 w
Equation(12-32) should not be used for Reynolds numbers below 6000 or for molten metals, which have abnormally low Prandtl number.
Estimation of wall temperature tw
The estimation of tw requires an iterative calculation based on the resistance equation
tm To tw ti 1 1 b do 1 do U o h o k dm hi di
At ordinary velocities the heat generated from fluid friction is negligible in comparison with the heat transferred between the fluids.

化工原理英文教材传热相变传热过程Heat transfer to fluids with phase change

In dropwise condensation
the condensate begins to form at microscopic nucleation sites. Typical sites are tiny pits, scratches, and dust specks.
The drops grow and coalesce with their neighbors to form visible fine drops.
It is the layer of liquid interposed between the vapor and the wall of the tube which provides the resistance to heat flow and therefore which fixes the value of the heattransfer coefficient.
化工原理 Principles of Chemical Industry
Heat transfer to fluids with phase change
Processes of heat transfer accompanied by phase are more complex than simple heat exchange between fluids since it concerns about thermodynamic and hydrodynamic.
friction losses in a condenser are normally small, so that condensation is essentially a constantpressure process.