水平细光管内R717流动沸腾换热及干涸研究

Study on Dry-out and Flow Boiling Heat Transfer for R717 in a Horizontal Smooth Mini-channel

本文探究了内径3 mm水平光管内氨(R717)的沸腾两相流换热特性以及环状流的干涸特性。实验工况:饱和温度−10∼10℃,热流密度10∼30 kW/m^(2),质量流率40∼200 kg/(m^(2)·s),干度0.1∼1。实验结果表明,质量流率、饱和温度及热流密度的增加都会强化沸腾换热。增加质量流率会强化环状流内的对流沸腾;增大饱和温度和热流密度主要会强化间歇流内的核态沸腾。在沸腾两相流中,干涸现象的发生往往伴随着传热系数的恶化。对干涸前、干涸后的传热系数分别进行拟合,并将拟合曲线的交点定义为干涸起始干度。拟合结果表明饱和温度、热流密度、质量流率的增加均会降低干涸的起始干度,加快干涸的进程,且干涸临界干度等于0.9±0.03,与可视化的结果一致。

The paper explores the characteristics of boiling two-phase flow heat transfer and the annular flow dry-out for ammonia(R717)in a horizontal smooth tube with an inner diameter of 3 mm.The purpose is to explore the characteristics of dry-out for the annular flow.The experimental conditions are:saturation temperature−10∼10℃,heat flux density 10∼30 kW/m^(2),the mass flow rate 40∼200 kg/(m^(2)·s),and the vapor quality 0.1∼1.The experimental results show that the increase of mass flow rate,saturation temperature and heat flux density will enhance boiling heat transfer.Increasing the mass flow rate will strengthen the convective boiling in annular flow;increasing the saturation temperature and heat flux density will mainly strengthen the nucleate boiling in intermittent flow.In the boiling two-phase flow,the dry-out phenomenon is often accompanied by the deterioration of heat transfer.The heat transfer coefficients before and after dry-out are fitted respectively.The intersection of fitted curves is defined as the initial vapor quality of dry-out.The fitting results show that the increase of saturation temperature,heat flux density and mass flow rate will reduce the initial dryness of drying and accelerate the drying process,and the critical vapor quality of dry-out is equal to 0.9±0.03,which is consistent with the visualization results.