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微通道冷凝换热实验研究
Experiments of Condensation Heat Transfer in Micro Channel Heat Exchanger
【作者】 王勋；
【导师】 王文；
【作者基本信息】 上海交通大学 ， 供热、供燃气、通风及空调工程， 2009， 硕士
【摘要】 微尺度器件的应用正处于积极的探索之中,系统也会变得越来越复杂,因而人们对微尺度的基本传热和流动过程中的理论和实验技术需求也与日俱增。工程应用中,微通道中的流动冷凝过程是微热管、电子芯片散热、紧凑式换热器、传感器冷却以及微电子系统冷却等领域的关键热物理过程。研究微通道中的冷凝过程,具有重要的工程应用前景和学术价值。目前对微通道中的单相流和沸腾流动已经有了比较深入的研究,但是对微通道中冷凝流动的研究却相对不足。本文介绍了微通道的尺寸结构、组装换热器、搭建测试实验台、采集实验数据和分析实验数据。设计出可以观察流型的微通道换热器、设计实验测试系统。微通道换热器实验设计和测试的关键是:1)密封微通道内高温高压并且具有腐蚀性的制冷剂关系到试验成败,制冷剂比水的实验难做,因为要求试验系统有较高的耐压能力(0.85MPa以上),并且试验同时要求对微通道的流动进行可视化观察,又因为透明材料的限制,给密封带来了困难,因为透明的有机材料不能焊接。本文经过探索,最后设计出合理的换热器结构解决了密封问题。2)各个元件的热容对微小流量实验影响较大,在微流量(10W以内)下,任何一个部件的不良热损失都可能占总换热量相当大的比重,而且不仅仅要考虑到散热,还应当考虑到与制冷剂以及水接触的各个部件的热容,热容影响试验的稳定性。本文实验材料尽量采用热容较小和体积较小的材料,使实验迅速达到稳定,控制热损失。3)控制小流量比较困难,实验工况的制冷剂质量流量相当小,利用现有的阀门来控制制冷剂提供罐流入换热片的流量有一定的难度,因为本文使用的不是一个闭环的系统,而是使制冷剂从提供罐流经各个实验传感器和换热片然后回到回收罐。对实验结果的分析得出如下的几点结论:1)在普朗特数范围为1<Pr<1.25下实验数据和Koyama的关联式预测比较接近。并且作者自己总结了实验测量范围内,微通道在低雷诺数下的冷凝换热关联式。2)总结了微通道内的流动阻力特性,实验所得出摩擦系数要比由Choi et al.、Pfahler和Blasius方程计算出的大很多,和Wu&Little方程的预测比较接近,绝对误差在±18.42%内。在微通道内的流动换热上,将试验数据和Fluent仿真结果进行对比,得出该仿真软件用于微通道内换热计算不是很准确,但是在定性上的趋势是正确的,比如说Fluent对模拟冷凝情况的大体位置是正确的,但是在各个地方的冷凝液的多少上有所不同。
【Abstract】 The application of micro scale devices are in active exploration, the system will become more and more complex, in micro-scale flow and heat transfer of basic theory and experiment technology, people are in the process of growing demand. The micro channel flow condensation process is used in electronic chip heat pipe, heat exchanger, compact micro refrigeration system cooling, sensors and laser diode cooling system of key areas such as heat physical process, micro channel has important engineering application prospect and academic value. Now the passage of single-phase flow and boiling flow has gotten thorough research, but in micro channel flow of condensing ware relative deficiency.This paper introduces the structure and micro channel heat exchanger, set up the assembly, test and analysis of data collected experimental data. Designed test system of micro channel heat exchanger (MCHX). The key of MCHX design and test are: 1) In high temperature and high pressure, The seal of micro channels and corrosive refrigerants in relation to the success or failure of the experiment, because the test system has to higher compression capacity (0.85MPa) and to test and requirements of micro channel flow visualization observation, because to find the restrictions, transparent material to seal is difficulty, and the organic material cannot be welded. Finally solved the sealing structure of heat exchanger .2) Each element of the heat capacity is of important, experimental flow within 10W, any parts of the thermal loss may be bad for a considerable proportion of heat transfer, and not just want to consider, also should consider to heat and water contact with refrigerants parts of the heat capacity, the heat capacity test of stability. This heat capacity of experiment materials is smaller and smaller. For refrigerant and the water side of heat transfer, using a piece of only 1mm thick PEEK to transfer and heat capacity of thermal resistance is much less.3) Controlling small flow is difficultly, the experimental condition of refrigerant mass flow is fairly small, using the existing valve to control the refrigerant has the certain difficulty, because this is not a closed loop system.The analysis of experimental results obtained as follows several conclusions: 1) Experimental data and the Koyama correlation forecast are closer. We summarized the experimental in the measurement range for the micro channel in low Reynolds number of condensing heat.2) We summarized micro channel flow resistance properties. Friction coefficient compare with Choi et al. equation and Pfahler,Blasius equation, and data are closer to the forecast by Wu&Little equation, the absolute errors are much lower.In micro channel flow field of the heat, comparing the test data and Fluent simulation results, we found the simulation software used in micro channel heat is not very accurate calculation, but in the trend is right on the qualitative, for example, Fluent in general conditions simulated condensation position is correct, but in every place of the condensate differ.