微圆管内R1234ze(E)流动沸腾的环状流特性模拟研究

本文建立了制冷剂R1234ze(E)在微圆管内流动沸腾过程中的环状流模型，对传热和气液两相流动压降进行了模拟研究。综合考虑重力、表面张力及气液界面剪切力的影响，模拟分析了周向液膜不均匀分布特性及该特性对流动与换热的影响，经验证，计算结果与已有实验结果吻合较好，此外还研究了不同因素对环状流区域表面传热系数与压降的影响。模拟结果表明：在流动起始区域，截面液膜厚度的分布受重力作用影响，随着流动沸腾过程的进行，该影响作用开始减弱，且有重力作用时的环状流平均表面传热系数高于无重力作用时的环状流平均表面传热系数，随着重力加速度的增加，环状流的平均表面传热系数不断增大；随着质量流速的增大，表面传热系数与压降均随之增大；随着管径增大，表面传热系数与压降均随之减小。

Simulation on Annular Flow of R1234ze(E) Flow Boiling in Micro-tubes

A theoretical model for annular flow of R1234ze(E) flow boiling in micro-tubes was proposed in this paper. The surface coefficient of heat transfer and pressure drop were calculated using the model. The variation in the liquid film thickness profile due to the gravitational effect, surface tension, and liquid-vapor interfacial stress was considered. The effect of the variation in the liquid film thickness profile on the heat transfer was analyzed. Furthermore, certain existing surface coefficients of heat transfer and empirical correlations of two-phase friction pressure drop were compared with the numerical results, and the comparison revealed deviations within 30%. The numerical results indicated that the variation in the liquid film thickness profile is evidently affected by gravity in the initial flow area, and the gravitational effect starts to weaken with the flow boiling process. The surface coefficient of heat transfer of annular flow with gravity was higher than that without gravity. Hence, the mean surface coefficient of heat transfer increased with gravitational acceleration. Furthermore, surface coefficient of heat transfer and pressure drop increased as the mass flux increased. Conversely, surface coefficient of heat transfer and pressure drop decreased as the diameters increased.