跨临界CO2热泵中蒸发器的数值模拟

运用CFD数值模拟的方法，通过编写自定义函数来设置气液质量转移源项、能量源项和管外壁温度边界条件，对简化后的跨临界CO2热泵热水器中蒸发器进行了数值模拟，得到了管内二氧化碳的温度场、压力场和气液相分布。模拟结果表明：CO2流体在进入弯管前已出现干涸现象，但进入弯管后干涸现象消失，液相气化速度变缓，出弯后重新恢复正常气化过程；CO2在管上部的气化速度要大于管下部，同时由于管壁换热作用，管四周的气化速度要大于管中心位置。

Numerical Simulation of the Evaporator in Trans-critical CO2 Heat Pump

The simplified CO2 evaporator was simulated through compiling UDF （User-Defined Function） to set mass transfer source team, energy source term and temperature boundary condition on outside wall of tube, by using the method of CFD. Temperature field, pressure field and phase distribution in CO2 evaporator was revealed. The results of simulation showed that the dry-up phenomena appears before CO2 entering the curved part of the pipe and disappears in the curved part of the pipe. Furthermore, the speed of CO2 gasification in the top of the pipe is faster than that in the bottom of the pipe. As the role of heat transfer in the wall of the pipe, the speed of CO2 gasification around the pipe is also faster than that in the center of the pipe.