超临界CO_2在电子膨胀阀内流动特性的数值分析

Numerical analysis of supercritical CO_2 characteristics flowing through electronic expansion valve

建立了超临界CO_2通过电子膨胀阀(EEV)降压过程的二维计算模型,采用均相流模型对超临界CO_2通过EEV的两相流动过程进行了数值模拟。结果表明超临界CO_2进入膨胀阀后,沿着工质的流动方向,其状态参数在开始变化不大,在接近阀芯最下端的部分,各状态参数开始剧烈变化。越靠近膨胀阀对称中心,CO_2压力越大,接近壁面处的压力最小。工质的流速最大的位置位于阀芯尖端,可达到179 m/s。CO_2工质流过阀芯尖端流阻最大处时,CO_2的压力急剧降低,两相间的质量传递率急剧增加,CO_2发生相变。随着EEV内CO_2压力的降低,CO_2气体份额持续增大,气体份额大小值与压力大小成反相关。

When supercritical CO2 flows through an electronic expansion valve （ EEV）, the state of CO2 changes from supercritical state to liquid, and finally into the gas-liquid two-phase state. A two-dimen- sion model of supercritieal CO2 flowing through an EEV was established, and the expansion process was simulated numerically using the homogeneous flow model. The results show that the parameters of supereriti- eal CO2 changed slightly when entering the expansion valve along the flow. At the bottom of the valve plug, the parameters exhibit a drastic change. The closer to the expansion valve symmetry center, the pressure of CO2 is higher. The pressure achieves minimum when close to the wall. The maximum flow rate of the work- ing fluid occurs at the tip of the valve plug, reaching 179 m/s. When CO= flows through the tip of valve plug, the CO2 pressure decreases drastically. The mass transfer rate between the two phases increases sharply, and the CO2 phase change occurs. With the decrease of CO2 pressure in EEV, the CO2 gas fraction increases continuously, and the gas fraction is inversely related to the pressure of COz.