蒸发10

Qq —— 潜热传热量,kJ/h
Q z —— 二次空气的总热,kJ/h
Pr —— 普朗特准则数；
Q —— 换热量，W r —— 气化潜热,J/kg
s1 —— 换热管水平间距，m s 2 —— 换热管竖直间距，m
NTU —— 传热单元数
tex —— 纱线的细度 n —— 开始运行实验台系统至吸水 性材料变干或补水时候的测量
Experimental Study on Heat and Mass Exchange Enhancement of Tubular Indirect Evaporative Cooler ABSTRACT
Evaporative cooling technique is attention-getting more and more because it has the unique advantage of energy-saving, economic, environmental protection and indoor air quality improving. This paper takes tubular indirect evaporative cooler as the research object, and aims at the problem of lower heat exchange effectiveness in tubular indirect evaporative cooler, in order to research the tubular indirect evaporative cooler with low consumed energy and high efficiency, the author carry on the research in theory and experiment from inserting spring wire into tubes and wrapping water-absorbing materials outside of the tubes. In the aspect of heat exchange enhancement of primary air, using for the methods in other tubular heat exchangers, choosing the appropriate heat exchange enhancement component that fit for tubular indirect evaporative cooler --spring wire, achieving the purpose of heat exchange enhancement in primary air. In the aspect of water-absor bing materials outside of tube, choosing the Coolplus water-absorbing materials through theoretical and experimental analysis, using it’s characteristic of moisture absorption and drying quickly, achieving the purpose of heat exchange enhancement between second air and water outside of the tube. The research found that the efficiency of heat transfer after insert spring wire into tube is higher 20%-30% than before insert spring wire, but the resistance of primary air increased only 5%-10%; when the water in the materials can wetting tubes, the predicted values of temperature, dampness and enthalpy matched well with the experimental data; when the water in the materials can not wetting tubes, between the exit and inlet of second air, the difference in temperature ascended, the difference in dampness and enthalpy is declined, the difference in efficiency of heat exchange is declined; the available water content in the water-absorbing wrapped outside of the tube is account for about 68%－75% to it’s maximum; the time interval of supplying water for water-absorbing materials is about 60%－65% that from the system start to end. In conclusion, the experiment of this paper provided feasible research method for developing tubular indirect evaporative cooler, and providing design guidelines for
hs —— 二次空气的焓值,kJ/kg hw —— 对应水膜温度 t w 的饱和空气
焓值, kJ/kg m —— 质量流量，kg/s
α —— 平均对流换热系数，W/m2・℃
λ —— 管外流体导热系数，W/m・℃
ρ —— 流体密度，kg/m3
σ —— 传质系数，m/s
m p —— 一次空气的质流量,kg/s m s —— 二次空气的质流量,kg/s
engineering application, it is good at applying tubular indirect evaporative in our country in theory and practice.
Written by Yugang Wang(Environmental Engineering) Directed by Prof. Xiang HUANG A.Prof. Junmei WU
下标 a —— 空气 w —— 水，水膜 p —— 一次空气 s —— 二次空气 1 —— 进口 2 —— 出口 db ——干球 wb ——湿球 min——最小值或最小量 max——最大值或最大量
目录Biblioteka 1 绪论 ············································································································ (1)
ϕ —— 相对湿度，%
μ —— 动力粘性系数，N.s/m2
M —— 管外包覆吸水性材料的保水
量,kg
ν —— 运动粘性系数，m2/s
Ø —— 管径，mm s —— 螺距，mm
p q —— 水蒸汽分压力,Pa
q —— 热流密度，W/m2
θ —— 润湿角，
ξ —— 阻力系数, Re —— 雷诺数 Nu —— 努谢尔特数
摘
要
蒸发冷却技术由于具有节能，经济，环保，改善室内空气品质的优点，得到 人们越来越多的关注。本课题以管式间接蒸发冷却器作为研究对象，就如何开发 和研究低能耗、高效率的管式间接蒸发冷却器，从管内插入螺旋线和管外包覆吸 水性材料两方面入手对管式间接蒸发冷却器的换热性能进行了比较全面的理论 与实验研究。 管式间接蒸发冷却器管内一次空气强化传热方面， 在吸收和借鉴了其它行业 中管式换热器强化传热方法的基础上， 选取了适合管式间接蒸发冷却器的管内强 化传热元件－螺旋线，达到了强化管内一次空气传热的目的。管式间接蒸发冷却 器管外包覆吸水性材料方面，通过理论与实验分析后优选由 Coolplus 纱线织成 的吸水性材料， 利用其吸湿快干的特性达到强化管外二次空气与水膜之间传热传 质的目的。 研究发现，管内插入螺旋线后其换热效率比插入之前提高了约 20%－30%， 而管内一次空气流动阻力只增加了 5%－10%；吸水性材料中的保水量能够完全润 湿铝箔管表面时，预测值与实验值符合的很好；吸水性材料中的保水量不能完全 润湿铝箔管表面时， 二次空气出口与入口的干球温度差 ∆τ s 上升， 含湿量差 ∆d s 与 焓差 ∆hs 下降，换热效率 E 降低；管式间接蒸发冷却器管外包覆吸水性材料中能 够维持稳定换热作用的有效可用保水量 M a 约占吸水性材料中最大保水量 M max 的 68%－75%；吸水性材料补水的时间间隔约为从系统开始运行到吸水性材料中 水分蒸发完毕所用时间的 60%－65%。 总之， 本课题的实验研究为管式间接蒸发冷却器的开发提供了可行的研究方 法，为工程设计提供了必要的依据，对管式间接蒸发冷却器在我国的应用具有一 定的理论与实践意义。 关键词：管式间接蒸发冷却器 强化传热传质 螺旋线 Coolplus 吸水性材料
Keywords: Tubular Indirect Evaporative Cooler (TIEC), Heat and Mass Exchange Enhancement, Spring Wire, Coolplus Water-Absorbing Material
基本符号表
A —— 换热面积，m2 B —— 大气压力，Pa τ—— 时间，s t —— 摄氏温度，℃ T —— 热力学温度，K V —— 速度，m/s