Numerical simulation of vapor volume fraction in a vertical channel under low-pressure conditions

Abstract

This numerical study involved investigating void behavior under low-pressure subcooled flow boiling by using an Eulerian approach (two-fluid model). In the simulation, a vertical pipe with a length of 0.15 m and diameter of 0.01229 m was considered. Different levels of uniform wall heat flux, mass flux, and inlet subcooling temperature were applied although a constant pressure of 1.65 bar was used for all the simulations. A sensitivity study of the empirical coefficients used to access the predictive capacity of the existing mass transfer models was conducted. Thus, the k-epsilon model was used for the turbulence of the fluid. The axial vapor volume fraction profile, liquid temperature is compared at the operating pressure. Furthermore, the most sensitive flow characteristics of the channel were identified. The results indicated that the predictions of numerical phase evolution relative to the experimental observations were in good qualitative agreement with those obtained in extant studies. Additionally, the changes in drag coefficients were helpful in precisely predicting the void fraction. A commercial CFD solver was used for the implementation of the model.