利用一基於流體體積(VOF) 之介面追蹤法求解薄膜沸騰

Abstract

本研究使用單一流體模型搭配CISIT 介面追蹤法求解雙相流之熱傳與質傳現象。其中所用的離散方法為有限體積法 (finite volume method)，而CISIT 介面追蹤法則是利用求解流體體積分率的傳輸方程式來追蹤介面之位置。利用介面處的質量與能量跳越條件求出相變化所造成的質量變化，並將其加入連續方程式中的源項作為修正。將動量方程式與連續方程式進行耦合，所得速度場將滿足介面處的質量跳躍函數。為了驗證相變化模型的準確性先求解具有理論解之相變化問題，發現溫度場之準確性與介面溫度梯度之計算都會影響模擬相變化的準確性。最後模擬一薄膜沸騰的氣泡生成，可觀察到氣泡的生成與成長過程中對於熱傳及質傳變化的影響。

A single-fluid model with a VOF based interface tracking method (CISIT) is used for simulation of two-fluid flows with heat and mass transfer in this study. The finite volume method is used as the discretiztion method. The motion of the interface is tracking by the solution of a transport equation for the volume fraction. By using the interface position obtained from the interface tracking method the heat flux which drives the phase change on interface can be calculated. The mass change across the phase boundary is computed by taking the mass and energy jump conditions at the interface. It is added as a source term in the continuity equation. This continuity equation is used in the pressure-velocity coupling algorithm. After the velocity field obtained from solving the momentum equation the jump condition for the continuity is satisfied. To assess the accuracy of this mode two test problems for which analytical solutions are available, are considered. It is shown that the precision of the temperature profile and the length used for calculating temperature gradients at the interface would affect the accuracy of simulation. Finally, a simulation of film boiling on a horizontal plate is presented. It shows that how the bubble growth affects the heat and mass transfer of the flow.