Bubble Behaviors in Saturated Flow Boiling Based on the VOF Model

Flow boiling in vertical pipes widely exists in nuclear reactors. The bubble motion and behavior attract more and more attention due to their influence on the heat transfer capacity. However, the most used two-phase flow model in numerical simulation, called Eulerian two-fluid model, is not able to obtain parameters of phase interfaces and provide an observed image of bubble movements. Therefore, the present study aims to simulate the bubble behavior and trajectory in the saturated flow boiling in the vertical pipe using VOF model which can treat the deformation of interfaces. Firstly, the bubble parameters were calculated based on existing bubble dynamic models. Then, the random generation of bubbles was simulated by directly adding mass and momentum sources into the flow region by the User Defined Function (UDF). Finally, the deformation, collapse, and coalescence of bubbles were simulated and predicted in bubbly flow. The feasibility of the newly proposed model is proved by comparing with experimental data and other simulation results. The present study provides a new idea for simulating the movement of a large number of bubbles in the saturated flow boiling in vertical pipes, which adopts bubble parameters as boundary conditions directly, instead of heat and mass transfer models. In comparison, the present model can greatly improve the calculation efficiency.