为研究分离式省煤器内循环工质的相变过程，使用Ansys Fluent中的mixture（混合流）模型对汽液两相流进行数值模拟。通过Lee′s蒸发冷凝模型对分离式省煤器的传热传质过程进行了迭代计算，获得了瞬态的气相图和温度场。在相变系统的加热过程中，可观察到蒸发段的液池内气泡的形成、合并、生长和上浮的全过程和在冷凝段壁面上凝结成液膜，并汇集返回蒸发段的全过程，计算得到的壁面温度与工程现场测量值相吻合，验证了模型的正确性。研究了热流密度、相变段内径、相变段长度比、充液量和冷凝段参数对相变系统总传热系数的定性关系，研究表明：在蒸发段管径30 mm、冷凝段温度320 K、热冷段长度比为1、热流密度800 W/m2情况下，充液率在0.2~0.8时分离式省煤器内循环系统可以稳定运行，充液率为0.4时，传热系数达到最大。研究结果为分离式相变换热系统的研究设计提供了参考。

In order to study the evaporationcondensation process in the separate type economizer,the Mixture model of the Ansys Fluent software is used to numerically simulate the vaporliquid twophase flow.The heat and mass transferring process of the separate type economizer is numerically simulated with Lee′s evaporationcondensation model,gas phase distribution and transient temperature field is obtained.The bubble formation,consolidation,growth and rise in the liquid pool of the evaporation section,and the vapor condensation and forming liquid film in the condensation section are all observed,it works well finally.The calculated wall temperature is in good agreement with the measurement engineering on site.Therefore,the correctness of the model is verified.Then,the effects of heat flux,the inner diameter of the phase transition section,the ratio of the phase change length,the liquid filling and the condensation section parameters on the heat and mass transfer process are investigated.It is found that when the diameter of evaporation section is 30 mm,the condensing section temperature is 320 K,the length ratio of hot and cold section is 1,the heat flux density is 800 W/m2,and the filling rate is 0.2-0.8,the inner circulation system of the separate type economizer can work well,with the maximum heat transfer coefficient under the filling rate of 0.4.The presented work is expected to provide a reference for the research and design of the separate type phase changing heat exchanger system .

TK124

]国家自然科学基金（51576036）；吉林省科技发展计划项目（20100506）