溴化锂溶液在亲水水平圆管表面降膜流动的数值模拟

Numerical simulation of falling film flow of aqueous lithium bromide solution over hydrophilic horizontal round tube

为了研究润湿性对水平管外降膜流动性能的影响,基于有限元法建立二维两相流模型,模拟了溴化锂水溶液在水平圆管外亲水表面不同润湿性（静态接触角0°~60°）的降膜流动过程;探究了液体在不同润湿性的水平圆管外壁铺展成膜的瞬态特性;分析了稳定后液膜厚度和液膜表面速度的分布特征.结果表明：当水平管外壁润湿性降低或静态接触角增加时,液体在水平管外铺展成膜所需的时间增加,液膜最前端液体的堆积量增大;达到稳定状态后液膜厚度沿周向呈先减小后增大,液膜速度沿周向呈先增大后减小的变化趋势;液膜最小厚度或最大速度位于周向角120°左右;根据液膜厚度沿周向角分布模拟值与实验数据的比较结果,对Nusselt液膜厚度表达式进行了修正.

In order to study the effect of wettability on falling film configuration over horizontal round tube,a two-dimensional two-phase flowmodel was developed based on the finite element method（ FEM） to simulate the falling film configuration of aqueous lithium bromide over hydrophilic horizontal round tube with different wettabilities（ static contact angle from 0° to 60°）. The transient behaviors of film flowprocess and the distributions of steady film thickness and velocity along horizontal tube were analyzed in detail. The results showthat when the static contact angle increases or the wall wettability decreases,the time spent on film spreading prolongs and the accumulation quantity of the liquid at the forefront of the film increases. The film thickness first decreases and then increases along the circumferential tube surface in the steady-state,while the velocity of the film first increases and then decreases along the circumferential tube surface,the film with the minimum thickness or the maximum velocity appears around circumferential angle of 120°. According to the comparison results between the simulation and the experimental data of the film thickness on a horizontal round tube,a modified correlation based on Nusselt theoretical formula is suggested.