R134a在水平环形通道内的凝结换热性能

摘要

A horizontal tube-in-tube heat exchanger was used as condenser in a air-source heat pump water heater,the condensation heat transfer characteristics of R134a in horizontal annular channel between the inner and the outer tubes was experimentally studied.The experiment tests the horizontal tube-in-tube condensation heat transfer coefficient with the change of heat flux,condensing pressure,dryness in different volume flow of water and inlet water temperature.The experiment was conducted at the range of water flow rate from 0.6 m3/h to 1.0 m3/h,the range of inlet water temperature from 15 ℃ to 60 ℃.The results showed that condensation heat transfer coefficient of R134a in annular channel decreased with the increase of heat flux and condensing pressure (temperature).The condensing pressure was 1.3 MPa,condensation heat transfer coefficient of R134a decreased by 6.9％,when heat flux increased from 18 kW/m2 to 20.5 kW/m2.The heat flux was 15 kW/ m2,the condensation heat transfer coefficient of R134a decreased by 5.8％,when condensing pressure increase from 1.78 MPa to 1.83 MPa.Local condensation heat transfer coefficient of R134a increased with the increasing dryness.The condensation pressure was 1.1 MPa and heat flux was 18.3 kW/m2,the local condensation heat transfer coefficient increased by 24.4％,when refrigerant dryness increased from 0.1 to 0.9.%在空气源热泵热水器中,对水平套管冷凝器环形通道内R134a的凝结换热特性进行实验研究.在冷凝器不同进水流量、进水温度时,实验测试了水平套管冷凝器凝结换热系数随热流密度、冷凝压力及干度的变化.实验工况为:冷凝器的进水流量为0.6 ～1.0 m3/h,进水温度为15 ～ 60℃.实验结果表明:水平环形通道内R134a的凝结换热系数随热流密度和冷凝压力(温度)的升高而减小,当冷凝压力为1.3 MPa,热流密度由18 kW/m2增加至20.5 kW/m2时,R134a的凝结换热系数减小了6.9％;当热流密度为15 kW/m2,冷凝压力由1.78 MPa增大至1.83 MPa时,R134a的凝结换热系数减小了5.8％.R134a的局部凝结换热系数随干度的增大而增大,当冷凝压力为1.1MPa,热流密度为18.3 kW/m2,制冷剂干度由0.1增大至0.9时,R134a的局部凝结换热系数增大了24.4％.