水平管内R1234yf流动冷凝换热和压降的实验研究

Analysis of Flow Condensation Heat Transfer and Pressure Drop of R1234yf inside the Tube

在1根光管、2根微肋管内对R1234yf两相流动冷凝换热进行实验,实验工况设定为冷凝温度(40±0.5)、(43±0.5)和(45±0.5)℃,质量流速为400~900 kg/(m^2·s),实验段进口制冷剂干度为0.80~0.85、出口制冷剂干度为0.15~0.20,进而从关联式拟合机理上分析各关联式对管内换热系数、压降的预测效果。结果表明:管内换热系数、压降均随流速的增加、冷凝温度的降低而增大,且微肋管内换热系数、压降均大于光管内换热系数及压降,其中,1号微肋管内换热系数最高,2号微肋管内压降最大;对于光管换热系数、压降,Thome关联式和Fridel关联式预测效果最佳,其预测平均误差均在3%以内,而Wang et al关联式和Chisholm et al关联式预测误差最大,其预测平均误差在25%以上;对于微肋管内换热系数、压降,Cavallini et al关联式和Haraguchi et al关联式分别表现出较好的预测效果,其平均预测误差分别-15.43%和-15.68%。

To analyze theoretically and verify experimentally the influences of experimental conditions and micro-fin tube structure on the heat transfer coefficient and pressure drop inside the tube,the two-phase flow condensation heat transfer experiment of R1234 yf was carried out inside one smooth and two micro-fin tubes.The experimental conditions were set as condensation temperatures of(40±0.5) ℃,(43±0.5) ℃ and(45±0.5) ℃,mass fluxes of 400 kg/(m^2·s)-900 kg/(m^2·s),vapor qualities of 0.8-0.85 and 0.15-0.2 at the inlet and outlet of test section,and then the prediction of the correlation on the heat transfer coefficient and pressure drop was analyzed based on the correlation fitting mechanism.The experimental result shows: the heat transfer coefficient and pressure drop all increase with the increase of mass flux and the decrease of condensation temperature,the heat transfer coefficient and pressure drop of micro-fin tube are greater than that of smooth tube,and the heat transfer coefficient of 1# micro-fin tube is the highest and the pressure drop of 2# micro-fin tube is the maximum.For the heat transfer coefficient and pressure drop inside the smooth tube,the correlations of Thome and Fridel have the best predictability with mean prediction error of less than 3%,while the correlations from Wang et al and Chisholm et al have the worst predictions with mean prediction error of less than 25%.For the heat transfer coefficient and pressure drop inside the micro-fin tube,the correlations in Cavallini et al and Haraguchi et al show a good prediction result and their mean prediction error is-15.43% and-15.68%,respectively.A high prediction accuracy of correlation not only can verify the accuracy of experimental data,but also can provide the direction of modification and development of the correlation.