亚临界CO2在缩放喷管中降压膨胀的数值模拟

忽略两相间的滑移速度，采用Fluent中的混合模型对亚临界CO2过冷液体进入缩放喷管降压膨胀产生气泡的两相流动过程进行了二维数值模拟.其中，气液两相间单位体积内的质量传递率采用空化模型理论进行计算.计算工况如下:喷管液体CO2进口压力为61MPa，温度为29315K，喷管出口为两相状态.计算结果显示，CO2工质流经喉部时，压力急剧降低，相间的质量传递率达到最大值，CO2工质发生相变；工质进入扩散段后，随着压力降低，气体份额不断增大，喷管出口压力为165MPa时，气体体积份额约为093.数值模拟值与实验值对比结果为，计算压力与实测压力值最大误差不超过101%，计算温度与实测温度值最大误差不超过19%.数值模拟揭示了亚临界CO2在喷管中的气液两相膨胀过程.

Numerical Simulation of Decompression Expansion of Subcritical CO2 Through Converging-Diverging Nozzle

Two phase flow generated from expansion of subcooled subcritical CO2 when flowing through a converging diverging nozzle was studied numerically using the mixture model of the Fluent with the sliding velocity neglected. Mass transfer rate between the two phases was calculated with the cavitation model under 61MPa and 29315K at the nozzle inlet. The results show that phase change occurs at the throat and the pressure drops steeply with the mass transfer rate reaching the maximum. The vapor volume fraction increases with decrease of pressure when the CO2 flows through the nozzle diverging section. When the pressure at nozzle exit gets to 165MPa， the volume fraction reaches 093. The comparison of calculated and experimental results show that the maximum relative error of pressure is less than 101% and that of temperature is less than 19%. Mechanism of the two phase flow expansion process of the subcooled CO2 through a converging diverging nozzle was well described by numerical simulation.