Enhancement of Condensation of a HFC-Refrigerant in a Horizontal Microfin Tube

对水平微翅管中制冷剂蒸汽的冷凝进行了实验和理论研究。实验包括HCFC123在水平管、光滑管和人字形管中冷凝过程的局部传热和压降测量，以及工业管镜下的流动观察研究。在低凝结水高汽速工况下，凝结水从翅片表面流向管顶和管底排水槽的流动情况良好。人字管的局部换热数据随着凝结的进行而减小，最大换热增强比为10。建立了螺旋沟槽水平微鳍管中膜状凝聚的理论模型。环形流型和分层流型是在目前和以前的研究人员进行的流动观察研究的基础上考虑的。环空流动模型假定所有的层流凝结水都是通过沟槽进行的。冷凝膜分为薄膜区和厚膜区。在翅片表面形成的薄膜区域，假定冷凝液在表面张力和蒸汽剪切力的联合作用下被排干。另一方面，在槽内形成的厚膜区，假定冷凝液是由蒸汽剪切力驱动的。对于分层流型，分层凝析液的高度由改进的Taitel和Dukler模型确定。对管内上部进行了考虑重力和表面张力联合作用的层流膜凝结数值计算。利用Carnavos建立的内翅片管的经验方程计算了管内下部的换热系数。将两种理论模型对四种制冷剂和四种管道的周向平均换热系数的理论预测结果与已有的实验数据进行了比较。一般来说，在高质量区域，环形流模型的换热系数高于分层流模型，而在低质量区域，分层流模型的换热系数高于分层流模型。大多数实验数据与两个理论预测中较高者的一致性在±20%以内。少

Experimental and theoretical studies have been performed for the condensation of refrigerant vapor in horizontal microfin tubes. The experiments includes the local heat transfer and pressure drop measurements, and flow observation study by use of an industrial borescope during condensation of HCFC123 in horizontal, smooth and herringbone tubes. The condensate flow from the fin surface to the drainage gutters located at the top and bottom of the tube seems quite well in the low condensate with high vapor velocity regime. The measured local heat transfer data for the herringbone tube decreased as the condensation proceeds, taking a maximum heat transfer enhancement ratio of ten.A theoretical model of film condensation in spirally grooved, horizontal microfin tubes has been developed. The annular flow regime and the stratified flow regime were considered on the basis of the flow observation studies performed by the present and previous investigators. The annular flow model assumes that al … More l the laminar condensate flow occurs through the grooves. The condensate film is segmented into thin and thick film regions. In the thin film region formed on the fin surface, the condensate is assumed to be drained by the combined surface tension and vapor shear forces. In the thick film region formed in the groove, on the other hand, the condensate is assumed to be driven by the vapor shear force. For the stratified flow regime, the height of stratified condensate was determined by a modified Taitel and Dukler model. For the upper part of the tube, numerical calculation of laminar film condensation considering the combined effects of gravity and surface tension forces was conducted. The heat transfer coefficient at the lower part of the tube was estimated by an empirical equation for the internally finned tubes developed by Carnavos.The theoretical predictions of the circumferential average heat transfer coefficient by the two theoretical models were compared with available experimental data for four refrigerants and four tubes. Generally, the annular flow model gave a higher heat transfer coefficient than the stratified flow model in the high quality region, whereas the stratified flow model gave a higher heat transfer coefficient in the low quality region. Most of the experimental data agreed within ±20% with the higher of the two theoretical predictions. Less