水平管内R1234yf的流动沸腾换热特性

通过实验研究了环境友好型制冷剂R1234yf在内径为0.5mm的水平圆形微通道内的流动沸腾换热特性，测量了不同工况下R1234yf的沸腾换热系数（HTC），并与传统制冷剂R134a进行了对比，分析了质量流速、热流密度和干度对换热系数变化规律的影响。实验条件为：饱和温度(17±1)℃，质量流速1000～2500kg/(m2·s)，热流密度25～143kW/m2。实验结果表明：R1234yf的换热系数随着热流密度的增大而显著增大，而质量流速和干度的影响较小，核态沸腾为其主导换热机制。对比R1234yf和R134a在相同工况下的换热特性，发现两种工质的平均换热系数差别较小，并均随着热流密度增大而逐渐增加，但是R1234yf发生干涸（Dryout）时的热流密度小于R134a。将实验数据与已有文献中的核沸腾主导的经验关联式的预测结果进行了对比，得到了较好的吻合。

Flow boiling heat transfer characteristics of R1234yf in horizontal microchannel

The flow boiling heat transfer characteristics of environmentally friendly refrigerant R1234yf in a 0.5mm horizontal circular microchannel were studied experimentally. The heat transfer coefficients (HTCs) of R1234yf were measured and compared with that of R134a, and the effects of mass flux, heat flux and vapor quality on HTC were analyzed. The saturation temperature was (17±1)℃, and the mass fluxes vary from 1000kg/(m²·s) to 2500kg/(m²·s) with heat fluxes ranging from 25kW/m² to 143kW/m². The experimental results showed that the HTC of R1234yf in 0.5mm microchannel increases with the increase of heat flux, while the mass flux and vapor quality showed a weak influence on it. The trend indicated that nucleate boiling was the dominant mechanism for flow boiling heat transfer. In addition, the heat transfer performance of R1234yf and R134a were compared under the same working conditions. The HTCs of R1234yf and R134a were almost identical and both increased with the increase of heat flux, but the heat flux for the occurrence of dryout of R1234yf was smaller than that of R134a. Finally, the experimental data for the two refrigerants were compared with two nucleate boiling-dominated correlations from literature and good agreements were obtained.