溴化锂溶液垂直降膜过程中流动与传热的数值模拟

Numerical Simulation on Flow and Heat Transfer of LiBr Solution along the Vertical Wall

采用流体体积(VOF)法捕捉自由界面,并应用连续表面力(CSF)模型,建立了垂直降膜波动模型,研究了溴化锂溶液垂直降膜过程中的波动过程,根据波动模型得到的界面信息,建立了以波速为动坐标系的固定界面传热模型,同时考察了波动对传热的影响,并建立了垂直降膜波动模型和固定界面传热模型。结果表明:一定入口频率的扰动发展为孤波和毛细波的组合波,孤波波峰处出现了循环流动,且在第一个毛细波波谷处出现回流。波动强化机理与Pr数有关,Pr数较大时,对流起主要作用,Pr数较小时,液膜减薄起主要作用。

The numerical model of falling film flow along a vertical wall was built up to investigate the wave behavior of aqueous LiBr solution using Volume of Fluid （VOF）model to track the free surfaces and using Continuous Surface Force （CSF） model for dynamic boundary conditions considering the effect of surface tension Based on the information of interface positions, a heat transfer model under the conditons of immobile interface was built up to investigate the effect of wave on heat transfer. The results showed that at some certain frequency the small disturbance could give rise to a big amplitude solitary roll wave and some small amplitude capillary waves. A big circulation flow at the wave peak and a backflow at the smallest film thickness were observed. Heat transfer model indicated that the enhancement mechanism depended on Pr number. The convective effect dominated when Pr number was large while the film thinning dominated when Pr number was small.