Thermal Optimization of Plate-fin Condenser Alternative Refrigerant Mixtures

本课题对可选制冷剂混合物板翅式冷凝器的热优化进行了实验和数值研究。采用替代制冷剂HFC134a、HCFCI23和HFC32及其混合物作为工质。通过该项目，明确了翅片结构对换热特性的影响。在数值研究中，分析了翅片垂直表面上的层流、膜状冷凝现象。得到了冷凝液膜厚度、热流压力、液膜半径以及垂直方向上的努塞尔数的三维分布。通过一系列的计算结果，揭示了翅片水平方向、平均高度、翅片间距、翅片厚度以及底板与翅片凹结合部半径的分布对液膜形状的影响，并考察了翅片形状参数对传热强化比的影响。垂直翅片表面上的平均努塞尔数Nu_m与键数Bo、伽利略数Ga_L、相变数Ph和平均努塞尔数Nu_<mo>相关。在实验研究中，对板式翅片换热器进行了NARMs HFC134a/HCFC123的冷凝实验。对比了纯制冷剂和混合制冷剂的冷凝传热特性，得到了冷凝液膜传热和制冷剂与冷却水单相传热的经验关联方程。利用实验得到的相关方程，提出了预测纳米粒子凝聚特性的计算方法。实验结果与预测结果吻合较好。还揭示了传质特性。

This project deals with the cxperimental and numerical research on the thermal optimization of plate-fin condenser for alternative refrigerant mixtures. Alternative refrigerants HFC134a, HCFCI23 and HFC32 and their mixtures are used as the working fluid. The effect of fin configuration on heat transfer characteristics has been clarified through this project.In the numericaI study, the laminar, film condensation on a finned vertical surface is analyzed. Thee-dimensional distribution of the condensed liquid fiIm thickness, the prcssure and the radius of liquid film in heat fiux and the Nusselt number along the vertical direction are obtained. From a series of calculation results, the effects of fin horizontal direction, the distributions of averaged height, fin pich, fin thickness and the radius of concave joint reion of base plate and fin on the liquid film shape are shown, and the effects of the fin shape parameters on heat transfer enhancement ratio are examined. The averged Nusselt number on a vertical finned surface, Nu_m, are correlated by the Bond number Bo, the Galileo number Ga_L, the phase change number Ph, and the averaged Nusselt number Nu_<mo>.ln the cxperimental study, the condensation of NARMs HFC134a/HCFC123 is carried out for a plate-fin heat cxchanger. The heat transfer characteristics of condensation of pure and mixed refrigerants are compared, and cmpirical correlation equations of the liquid film heat transfer with condensation and the single phase heat transfer of refrigerant and cooling water are obtained. The calculation method to predict the condensation chararacteristics of NARMs is dcveloped using the cmpidcal correlation equations obtained experimentally. It is shown that agreement between cxperiment and prediction is good. The mass transfer characteristics are also revealed.