低质量流率蒸汽真空水平管内凝结传热特性的实验研究

Experimental study on condensation heat transfer characteristics of low mass flow rate steam in a vacuum horizontal tube

对换热长度为3.4 m、内径为38 mm的真空水平管内的蒸汽凝结流动换热特性进行了实验研究。分析了蒸汽质量流率小于9 kg/(m^(2)·s),蒸汽饱和温度为50、60和70℃,换热温差为3~7℃时对凝结过程的影响。通过对分层流动冷凝换热机理分析,建立了热分区角计算模型。实验结果表明,热分区角随着质量流率的增加而增加,随着传热温差的增大而增大;饱和温度对管内凝结的局部传热系数和热分区角影响较小。通过以热分区角为分区界限,建立了局部传热系数经验关联式,在预测实验工况下,对于管顶部膜状冷凝区,预测精度在±25%以内;对于管底部冷凝液对流换热区,预测精度在+25%~-35%。

The heat transfer characteristics of steam condensation flow in a vacuum horizontal tube with the length of 3.4 m and inner diameter of 38 mm were studied experimentally.The steam mass flow rate is less than 9 kg/(m^(2)·s),steam saturation temperatures are 50,60 and 70℃,and steam inlet saturation temperature and cooling water inlet temperature difference is from 3 to 7℃.By analyzing the condensation heat transfer mechanism of stratified flow,the calculation model of thermal partition angle was established.The results of experiments indicate that the thermal partition angle increases with the increase of mass flow rate and heat transfer temperature difference.The saturation temperature has little effect on the local heat transfer coefficient and the thermal partition angle.The empirical correlation of local heat transfer coefficient is established by taking the thermal partition angle as the zone boundary.Under the experimental conditions,the predicted results in filmwise condensation area at the top of the tube are within ±25% and the predicted results in convective heat transfer zone of condensate at the bottom of the tube are from +25% to -35%.