微细管道内R141b沸腾气液两相流动与换热特性数值仿真

Numerical Simulations on Two-Phase Boiling Flow and Heat Transfer of Refrigerant R141b in Micro/Mini-Channel

为探究微尺度管道内沸腾气液两相流动与换热机理,采用基于VOF多相流模型的数值方法研究了制冷剂R141b在水平微细管道内的流动沸腾换热过程,获得了制冷剂R141b在管道内的流型、温度、速度及表面传热系数分布,分析了制冷剂R141b在管道内流动沸腾换热的基本规律和气泡运动特点。研究表明,制冷剂R141b在微细管道内流动沸腾依次出现单相流,泡状流,受限泡状流,弹状流,间歇状流,雾状流等典型流型。制冷剂R141b在微细管道内温度沿轴向逐渐升高,速度沿轴向逐渐增大,表面传热系数沿轴向先增大后减小。由于质量流速的增大使得制冷剂气相和液相的流动速度增加,表面传热系数随之增大:相同热流密度下,计算的大质量流速工况较小质量流速工况的表面传热系数平均增幅为21.4%;热流密度的增大会加快制冷剂液相向气相转变的速度,表面传热系数随之增大:相同质量流速下,计算的大热流密度工况较小热流密度工况的表面传热系数平均增幅为23.9%。

In order to investigate the flow and heat transfer mechanism of gas-liquid two-phase in micro/mini-channel,the flow boiling heat transfer of the refrigerant R141 b in horizontal micro/mini-channel was simulated using VOF multiphase flow model. The distribution of two-phase flow regimes,temperature,velocity and boiling heat transfer coefficients were obtained. The characteristics of the flow boiling heat transfer and bubble movement were analyzed. The results show that two-phase flow pattern maps in horizontal micro/mini-channels include single phase flow,bubbly flow,confined bubble flow,slug flow,intermittent flow,mist flow,and so on. Vapor quality,temperature and velocity increase gradually along the axial direction,the boiling heat transfer coefficients increase firstly and begin to decrease after the peaks. As the increase of the mass velocity and heat flux,boiling heat transfer coefficient increase significantly. This is because that the flow velocity of the refrigerant increases with the increasing mass flux and the velocity of liquid phase transition to gas phase increases with the increasing heat flux. On the same conditions of heat flux,the heat transfer coefficient in the conditions of large mass flux increased 21.4% averagely than the small mass flux. On the same conditions of mass flux,the heat transfer coefficient in the conditions of large heat flux increased 23.9% averagely than the conditions of small heat flux.