微通道换热器的设计与实验研究.pdf

上海交通大学硕士学位论文微通道换热器的设计与实验研究姓名：李庆友申请学位级别：硕士专业：@指导教师：王文20060201上海交通大学硕士学位论文I微通道换热器的设计与实验研究摘 要微小型化是当代科技发展的重要方向之一近些年来微小通道紧凑式换热器在汽车宇航电子和制冷等行业内的应用越来越广但是对于微小型通道内的流动传热机理等问题仍然还存在着很多争论这方面的基础研究仍然处于初步阶段本文首先分别从单相和两相的角度总结了近年来学者对微通道内的流动和传热的研究成果适当分析了微通道与大通道微小通道内流动传热机理的差异其次为了设计出比较适合的微通道换热器本文应用 Fluent 软件对通道结构进行了流动特性的定性分析同时从能力守恒的角度建立了微通道的数学模型并用Fortran 语言编写程序对制冷剂在不同截面(0.30.2,0.30.3mmmm创0.30.4mm´0.30.5mm´和0.30.6mm´)尺寸和流量(700kg/m2s867 kg/m2s和 1033 kg/m2s)情况下流动和传热特性进行仿真根据理论设计的指导作者设计出了实验所测试的微通道换热器同时利用现有的机械加工手段完成了对该微通道换热器的加工微槽道是采用线切割的方法加工其它部件直接由普通机床所完成为了能够获得更加可靠的数据作者设计了两套实验方案对微通道换热器进行研究一是单相实验系统实验工质是水二是两相实验系统实验工质是 R134a单相水系统实验系统是一个开放的系统摘 要II由气压驱动部分部件测试部分加热部分流量测量部分和数据采集与存贮部分这种结构的特点是构造简单流量易控制和成本较低两相制冷剂系统是一个闭式系统主要由小型制冷系统测试旁路系统加热系统和数据采集与存贮系统由于时间原因本文所完成的实验仅是单相水系统实验所测试的微通道截面尺寸为 200x100m有效长度长度为 70mm流动传热实验的工况范围是质量流量 G450750kg/m2s加热直流电压 U616V实验研究的结果表明微通道内传热与流动特性跟常规理论存在着明显的差异作者分析主要原因可能是由通道尺寸的减小引起了流体的 Kn数与常规尺度通道的不同从而使得通道表面的粗糙度L/Dh流体的物性等因素对流体流动和传热的影响更加显著关键词微通道换热系数摩擦系数水上海交通大学硕士学位论文IIIDESIGN AND EXPERIMENTAL INVESTIATION OF THEMICRO-CHANNEL HEAT EXCHANGERABSTRACTMicrominiaturization is one of important directions of contemporaryscientific and technical development. In the past a few years, micro- andmini-channel heat exchangers have been extensively used in the industries ofautomobile, aerospace, electronics and refrigeration. However, there are somany controversies in related theoretical problems, such as flow and heattransfer mechanism. So these investigations are still in an immature stage.First of all, this paper summarized contemporary research findings on flowand heat transfer inside micro-channel from single and two-phase viewpoints.Secondly, in order to design the most applicable micro-channel heatexchanger, commercial software of Fluent6.2 is adopted to make a qualitativeanalysis of flow behaviors of micro-channels. Furthermore, mathematicalmodelings of micro-channel were built, and according to these modelingscodes of Fortran were programmed to simulate performance of refrigerant(R134a) on flow and heat transfer inside the micro-channel under differentflow rate (700kg/m2s867 kg/m2s 和 1033 kg/m2s) and cross-sectionaldimension (0.30.2,0.30.3mmmm创0.30.4mm´0.30.5mm´和0.30.6mm´). Theauthor designed a micro-channel heat exchanger in terms of theoretical摘 要IVanalysis, meanwhile, machining methods were used to machine the micro-channel heat exchanger.In order to obtain more reliable data, author designed two kinds ofexperimental setups to make an investigation, one is single-phaseexperimental system (working medium is water), the other is two-phaseexperimental system (working medium is R134a). The single-phaseexperimental system is open, including pressure-driven part, testing part,heating part, part of flow measurement and data acquisition part. The two-phase experimental system is composed of mini-refrigeration system, testingby-pass system, heating system and data acquisition, and it is a close system.Experiment conducted in this thesis is single-phase, cross-sectionaldimension of micro-channel tested is 200x100m, effective length is 70mm.Experimental work conditions are: mass flow rate (G), 450~750 kg/m2s,heating voltage (U), 6~16DV.Experimental results show: heat transfer and flow behaviors of micro-channels differ from conventional channels. Because decrease of dimensionof micro-channels causes Kn number of fluid to change, some factor, just likesurface roughness of micro-channel, (L/Dh), fluid property etc., becomemore important to micro-channel.Keywords: micro-channel, coefficient of heat transfer, friction factor, water上海交通大学硕士学位论文VII符号表英文字母A截面面积Q加热功率WhD水力直径mmq热流W/m2f达尔西阻力系数T温度G单位面积上的质量流量kg/m2su轴向速度m/sh工质的焓值kJ/kgU电压VH通道深度mmW通道宽度mmk导热系数v比容m3/kgm53(7):175–93. [3] Satish G. Kandlikar. Fundamental issues related to flow boiling in minichannels and microchannels. Experimental Thermal and Fluid Science, 26(2002): 389-407. [4] P. Wu, W.A. Little, Measurement of friction factors for the flow of gases in very fine channels used for microminiature Joule–Thompson refrigerators, Cryogenics 23 (1983) 273–277. [5] R.E. Acosta, R.H. Muller, W.C. Tobias, Transport processes in narrow (Capillary) channels, AIChE J. 31 (1985) 473–482. [6] X.N. Jiang, Z.Y. Zhou, J. Yao, Y. Li, X.Y. Ye, Micro-fluid flow in microchannel, in: Proceedings of Transducers ’95, Stockolm, Sweden, 1995, pp. 317–320 [7] X.N. Jiang, Z.Y. Zhou, X.Y. Huang, C.Y. Liu, Laminar flow through microchannels used for microscale cooling systems, in: Proceedings of 97 IEEE/CPMT Electronic Packaging Technology Conference, 1997, pp. 119–122. [8] Z.X. Li, D.X. Du, Z.Y. Guo, Experimental study on flow characteristics of liquid in circular microtubes, in: G.P. Celata, et al. (Eds.), Proceedings of International Conference on Heat Transfer and Transport Phenomena in Microscale, Begell House, New York, USA, 2000, pp. 162–168. [9] J. Judy, D. Maynes, B.W. Webb, Liquid flow pressure drop in microtubes, in: G.P. Celata, et al. (Eds.), Proceedings of International Conference on Heat Transfer and Transp。