Microchannel Condensation Heat Transfer

微通道冷凝传热

• 批准号: EP/H014349/1
• 负责人: John Rose
• 金额: $ 39.12万
• 依托单位: Queen Mary University of London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FH014349%2F1
• 关键词: Microchannel; Condensation; Heat; Transfer

Around 50% of the electricity consumption of large food retailers in the UK is for cooling chilled and frozen food cabinets. Their total annual electrical energy consumption is almost 10 TWh. As early as 1994, 10% of floor space in the UK was serviced by air-conditioning. The figure is now more than 25% for buildings constructed during the past 10 years. The condenser is a key component of vapour compression refrigeration and air conditioning plant. Wide implementation of well-designed microchannel condensers would lead to a reduction of around 20% in power requirement. In the UK this represents a significant decrease in fossil fuel consumption and carbon dioxide emissions. Improved designs would also be significantly smaller, have smaller fluid inventories and possibly lower capital cost. Established design methods for larger channels fail for channel dimensions around 1 mm owing to surface tension effects. A wholly-theoretical model, valid for condensation of any fluid in microchannels, has been developed at Queen Mary (QM) under research programmes supported by EPSRC. Available experimental data are insufficient in number and reliability, and do not cover a sufficiently wide range of fluid properties, to validate and extend the theory. In most investigations vapour-side, heat-transfer coefficients are deduced from overall coolant-to-vapour measurements and are consequently of relatively low accuracy. Four correlations representing measurements for R134a agree to within about 30% for this fluid but differ by a factor of around 4 for ammonia. Existing correlations evidently do not correctly capture fluid property effects.The QM theoretical model has no recourse to experimental data. It includes transverse flow due to surface tension as well as shear stress and gravity effects and has been used to generate results for various fluids, channel shapes and dimensions, vapour flow rates and channel inclinations. The predictions fall within the ranges of the results given by the correlations. Theoretical results for seven fluids have been widely disseminated in conference proceedings (9 papers) and in archival journals (5 papers). A simple algebraic relation between two dimensionless parameters has recently been developed which predicts, very accurately, numerically-obtained results for the surface tension dominated flow regime for different channel cross section, fluids, vapour flow rates and temperature differences. Similar simplified results will be obtained for the flow regimes upstream and downstream of the surface tension dominated region so as to provide readily usable formulae for complete condenser design.An innovative technique will be used to measure local temperatures and heat fluxes in microchannels. A new apparatus has been designed in which parallel microchannels (1.5 mm x 1.0 mm) pass through the centre of a copper block (30 mm x 40 mm x 500 mm long) in which temperatures are very accurately measured (to within 0.05 K) at 98 precisely-known (to within 0.3 mm) locations. The observations will be used in inverse solutions of the conduction equation to determine local vapour-side surface temperatures (to within 0.1 K) and heat fluxes (to within 5%). Flow visualization studies will also be performed in which the upper part of the test block is replaced by glass so that the flow in the channels may be observed using high-speed photography.Two fluids (steam and FC72) with widely different thermophysical properties, notably surface tension, will be used. These data will provide a stringent test of the present theory and facilitate its extension to cover other flow regimes. The final model should be valid for any fluid, channel geometry, vapour flow rate and vapour-to-wall temperature difference. This will facilitate design and optimisation of a new generation of large scale refrigeration and air conditioning equipment.

在英国，大型食品零售商大约50%的电力消耗用于冷却冷藏和冷冻食品柜。他们每年的总用电量几乎是10TWh。早在1994年，英国就有10%的建筑面积由空调提供服务。这一数字现在超过了过去10年建造的建筑物的25%。冷凝器是蒸汽压缩制冷空调装置的关键部件。设计良好的微通道电容器的广泛应用将导致电力需求减少约20%。在英国，这代表着化石燃料消耗和二氧化碳排放的显著减少。改进后的设计也将显著缩小，拥有更少的液体库存，并可能降低资本成本。由于表面张力效应，已建立的较大通道的设计方法在通道尺寸约为1 mm时失败。在EPSRC支持的研究计划下，玛丽皇后大学(QM)开发了一个完全理论的模型，适用于微通道中任何流体的冷凝。现有的实验数据在数量和可靠性方面都不够充分，也没有涵盖足够广泛的流体性质，无法验证和推广该理论。在大多数研究中，蒸汽侧的换热系数是根据整个冷却剂对蒸汽的测量得出的，因此准确度相对较低。代表R134a测量值的四个关联式对于这种流体的一致性在30%以内，但对于氨的差异约为4倍。现有的关联式显然不能正确地捕捉到流体性质的影响。QM理论模型不依赖于实验数据。它包括由表面张力以及剪应力和重力效应引起的横向流动，并已用于生成各种流体、通道形状和尺寸、蒸汽流量和通道倾斜度的结果。这些预测落在关联式给出的结果范围内。关于七种流体的理论结果已在会议记录(9篇论文)和档案期刊(5篇论文)中广泛传播。最近发展了两个无量纲参数之间的一个简单的代数关系，它非常准确地预测了不同通道截面、流体、蒸汽流量和温差下以表面张力为主的流型的数值结果。对于表面张力控制区的上游和下游流型，将得到类似的简化结果，以便为整个冷凝器的设计提供易于使用的公式。一种创新的技术将用于测量微通道中的局部温度和热流密度。设计了一种新的装置，其中平行的微通道(1.5 mm x 1.0 mm)穿过铜块(30 mm x 40 mm x 500 mm长)的中心，在98个精确已知(到0.3 mm)的位置非常精确地测量(到0.05K)温度。观测结果将用于传导方程的逆解，以确定局部蒸汽侧表面温度(至0.1K以内)和热通量(至5%以内)。还将进行流动可视化研究，将测试块的上部替换为玻璃，以便可以使用高速摄影来观察通道中的流动。将使用两种热物理性质(特别是表面张力)非常不同的流体(蒸汽和FC72)。这些数据将对目前的理论进行严格的检验，并有助于将其推广到其他流型。最终的模型应适用于任何流体、通道几何形状、蒸汽流量和汽壁温差。这将有助于新一代大型制冷和空调设备的设计和优化。

项目成果

Pressure Drop During Condensation in Microchannels

微通道中冷凝过程中的压降

• DOI: 10.1115/1.4024465
• 发表时间: 2013
• 期刊: Journal of Heat Transfer
• 作者: Wang H

Heat Transfer and Pressure Drop During Laminar Annular Flow Condensation in Micro-Channels

• DOI: 10.1080/08916152.2012.737261
• 发表时间: 2013-03
• 期刊: Experimental Heat Transfer
• 影响因子: 3.5
• 作者: H. S. Wang;J. Rose

Scale effect on flow and thermal boundaries in micro-/nano-channel flow using molecular dynamics-continuum hybrid simulation method

使用分子动力学-连续介质混合模拟方法研究微/纳米通道流动中流动和热边界的尺度效应

• DOI: 10.1002/nme.2683
• 发表时间: 2010-01-08
• 期刊: INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING
• 影响因子: 2.9
• 作者: Sun, Jie;He, Ya-Ling;Tao, Wen-Quan
• 通讯作者: Tao, Wen-Quan

Heat transfer and pressure drop during condensation of R152a in circular and square microchannels

• DOI: 10.1016/j.expthermflusci.2013.01.002
• 发表时间: 2013-05
• 期刊: Experimental Thermal and Fluid Science
• 影响因子: 3.2
• 作者: Na Liu;Junming Li;Jie Sun;Hua Sheng Wang

Comparison of theory and measurements for condensation in microchannels

微通道内冷凝理论与测量的比较

• 发表时间: 2013
• 作者: Wang HS