大尺寸平板上降膜蒸发传热的数值模拟

Numerical Simulation of Water Film Evaporation Heat Transfer in Large Flat Plate

第三代先进压水堆中非能动安全壳冷却系统对于保护核电站安全具有关键作用,因此进行降膜换热机理研究具有重要意义。前人对于降膜蒸发的试验研究很多,但鲜见平板降膜蒸发的数值模拟。现有模拟方案由于计算量的限制,局限于二维模型或小尺寸的三维模型,且只分析了蒸发过程中的温度变化等。提出采用CFD软件Fluent中的Eulerian wall film模型与Mixture Species Transport模型耦合的方案对水膜试验台架全尺寸三维模型(板长:5 m,板宽:1.2 m)下的降膜蒸发和传热传质现象进行了数值模拟,通过对比试验与模拟结果,确定了EWF模型中蒸发常数的正确设置,且蒸发率、换热量以及舍伍德数吻合较好,最大偏差小于20%,验证了建立的数值模拟方案的正确性。在此基础上,进一步数值分析了水膜蒸发换热的影响因素,其中:入口水流量、入口风温、入口水温和平板倾角对总换热量影响很小,可以忽略;入口风速是影响总换热的重要因素,入口风速越大,总换热量越大。以上结论均是在保证水膜全覆盖板面的条件下得到的。为接下来的PCCS全尺寸模型的计算提供了理论依据。

The passive containment cooling system in the third-generation advanced pressurized water reactor has a key role in protecting the safety of nuclear power plants,thus,it is of great significance to study the hydrothermal mechanism of water film.There are many experimental studies on the evaporation of falling film,but the numerical simulation of the evaporation of the falling film is rare.The existing simulation scheme is limited to a two-dimensional model or a small size 3d model due to the limitation of calculation,and only the temperature changes in the evaporation process are analyzed.A numerical simulation of water film evaporation and heat transfer in the full-size water film test bench 3d model was carried out by using the method of Eulerian wall film model and the coupling of the model of the Species Transport model in Fluent,by comparing test results and simulation results,evaporation rate,heat change and Sherwood number anastomoses well,the maximum deviation is less than 20%,verifying the mathematical model and the simulation scheme.On this basis,further simulation calculated the process of the evaporation process of the water film to obtain the influence of each factor on heat exchange.The inlet water flow、inlet water temperature and the gentle plate angle,the inlet air temperature have little influence on the heat exchange,which can be ignored;Inlet speed is an important factor affecting heat exchange,the greater the inlet wind speed,the greater the total heat exchange.All the above conclusions are obtained under the condition that the water film is covered with panes.The theoretical basis is provided for the calculation of the full-size model of PCCS.