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

对制冷剂蒸汽在水平微翅片管中的冷凝过程进行了实验和理论研究。实验包括对HCFC123在水平管内、光滑管内和人字形管内冷凝过程的局部换热和压降测量，以及利用工业开孔镜进行流动观测研究。在低凝结、高汽速的情况下，冷凝水从翅片表面流向管子顶部和底部的排水沟看起来很好。人字管的局部换热数据随着冷凝的进行而减小，最大强化比为Ten。建立了螺旋槽水平微翅片管内气膜冷凝的理论模型。在现有和前人研究成果的基础上，考虑了环状流型和分层流型。环状流模型假定Al…L越多，冷凝液层流就越容易流过凹槽。冷凝膜被分成薄膜区和厚膜区。在翅片表面形成的薄膜区，冷凝液被假定为在表面张力和蒸汽剪切力的共同作用下排出。另一方面，在凹槽中形成的厚膜区，冷凝液被认为是由蒸汽剪切力驱动的。对于层状流态，层状冷凝液的高度由修正的Taitel和Dukler模型确定。对于管子上部，考虑重力和表面张力的共同作用，进行了层流液膜凝结的数值计算。管子下部的换热系数由CarNavos提出的内翅片管经验公式估算，用两种理论模型预测的周向平均换热系数与现有的四种制冷剂和四种管子的实验数据进行了比较。总体而言，环状流模型在高品质区的换热系数高于分层流模型，而分层流模型在低品质区的换热系数较高。大部分实验数据与两个理论预测值中的较高者在±20%以内吻合。较少

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