R134a在风冷分液式冷凝换热器中的换热性能研究

Study on Heat Transfer Performance of R134a in Air-Cooling Liquid-Vapor Separation Condenser

对于管内冷凝,随着冷凝过程的进行,冷凝液膜会在壁面处不断积累,增加换热热阻。加入分液结构可以将冷凝液及时分离,改善下游蒸汽干度,再生"入口段薄液膜效应",提高管内换热换热系数。本文针对具有U型分液结构的管翅式冷凝换热器,开展了不同风速、不同蒸气质量流速下的换热器整体换热性能研究,并对3 mm和6 mm管径的分液管的分离液量进行了测量。实验结果表明:随着蒸汽质量流速的增加,具有分液结构的翅片冷凝换热器整体换热系数增加,但当质量流速大于250 kg·m-2·s-1时,管内换热基本呈现单相换热,整体换热系数降低;随着冷却风速的增加,换热器整体换热系数增加;与3 mm分液管径相比,6 mm分液管径下,分液量提高了20%~50%,并且因为分液量的提高,管内干度更高,换热器整体换热系数提高了20%~50%。

In the process of in-tube condensation,the condensate film would accumulate continuously on the tube wall,increasing the thermal resistance.Inserting the liquid-vapor separation structure could help timely separate the condensate,improving the quality of the downstream flow and regenerating the"thin liquid film effect in the inlet section".Then,the heat transfer coefficient inside the tube could be improved.In this paper,the overall heat transfer performance of the finned tube condenser with a U-tube liquid-vapor separator was investigated.The experimental conditions involved different wind speeds and different mass fluxes.The mass flow rates of the condensate separated through the separation tubes with diameters of 3 mm and 6 mm were measured.The experimental results showed that with the increase of the mass flux,the overall heat transfer coefficient of the finned tube condenser with the liquid-vapor separator increased,but when the mass flux was more than 250 kg-m-2.s-1,the heat transfer inside the tube basically presented single-phase heat transfer and the overall heat transfer coefficient decreased.Then,with the increase of the wind speed,the overall heat transfer coefficient increased.Finally,compared with the separation tube with diameter of 3 mm,the separation tube with diameter of 6 mm could increase the mass flow rate of the condensate separated by 20%~50%.And as a result,the quality inside the tube was increased and the overall heat transfer coefficient was increased by 20%~50%.