Abstract:

Nowadays, more and more attention has been paid to the new low GWP (global warming potential) refrigerant R1234ze(E), which is one of the ideal alternatives for R134a. In this work, the flow boiling heat transfer coefficients of R1234ze(E) and R134a were measured inside an 8 mm ID horizontal tube. The experimental results were obtained over the saturation temperature of 10℃ with heat fluxes ranging from 5.0 to 10.0 kW·m^-2 and mass fluxes ranging from 300 to 500 kg·m^-2·s^-1. The influences of mass flux, heat flux and quality on the heat transfer coefficients were discussed. The results showed that the local flow boiling heat transfer coefficients of R1234ze(E) and R134a increased with increasing mass flux and heat flux. The local heat transfer coefficient of R1234ze(E) was around 14.68% lower than that of R134a at the mass flux of 300 kg·m^-2·s^-1, while the local heat transfer coefficient deviation between R1234ze(E) and R134a reduced to 7.35% when the mass flux reached 500 kg·m^-2·s^-1. Additionally, the experimental data of local heat transfer coefficients were compared with four well-known correlations available in literatures. The results indicated that Kandlikar correlation provided the best prediction of the local heat transfer coefficients for both R1234ze(E) and R134a. Approximately 90% of the experimental points are in an error bandwidth of ±25% of the prediction, and the average deviations are found to be 23.13% and 11.50% for R1234ze(E) and R134a, respectively.

Key words: R1234ze(E), R134a, flow boiling, heat transfer correlation, horizontal circular tube

摘要：

新型制冷剂R1234ze(E)(trans-1,3,3,3-tetrafluoropropene)因较低的GWP值备受制冷行业关注,有望替代R134a。在内径为8mm水平圆管内对R1234ze(E)流动沸腾换热特性进行实验研究,并在相应实验工况下与R134a进行对比。本研究的实验工况:流动沸腾换热的饱和温度为10℃±0.5℃,热通量为5.0和10kW·m^-2,质流密度范围为300~500kg·m^-2·s^-1。分析质流密度、热通量以及干度对R1234ze(E)和R134a饱和流动沸腾传热系数的影响。结果表明,R1234ze(E)和R134a的流动沸腾传热系数随质流密度和热通量的增大而增大;在低质流密度300kg·m^-2·s^-1工况下,R1234ze(E)传热系数较R134a偏低14.68%左右,但随质流密度增大到500kg·m^-2·s^-1,其偏差缩小为7.35%。最后将实验结果同4种常见预估关联式进行比较,结果表明Kandlikar关联式计算结果较优,全工况范围内Kandlikar关联式对R1234ze(E)和R134a的预估值与90%的实验数据偏差在±25%以内,平均偏差分别为23.13%和11.50%,满足工程设计要求。

关键词: R1234ze(E), R134a, 流动沸腾, 传热关联式, 水平圆管