Numerical investigation of the effect of bump and indent inside a vertical tube on the subcooled flow boiling and critical heat flux

Abstract

One of the essential industry problems is the critical heat flux (CHF) phenomenon in the flow boiling regime which leads to the temperature jumping and damaging to the systems. Increasing the vapour volume fraction decreases the heat transfer coefficient, and finally, temperature jump will occur. Also, the existence of the bumps and indent in the flow domain changes the flow pattern. In this study, by considering bumps and indent in the tube, the boiling of fluid flow in the vertical tube is discussed. For modelling and simulating the problems, the Euler-Euler model for studying the interaction of the liquid-vapour phases was used. Some models and material specifications are declared using the user-defined function (UDF) codes to the ANSYS Fluent program. The results show that the existence of bumps and indent inside the tube causes the flow of liquid phase to be less redirected in comparison to vapour phase flow due to having more momentum; therefore, at the end of the bumps in the tube, the amount of vapour volume fraction near the wall rises sharply. By increasing the flow mass flux, the vapour volume fraction at the end of bumps increases which lead to decreasing CHF value. It has also observed that if there are bumps and indents inside the tube, there will be no significant change in the liquid flow and vapour volume fraction in the other parts of the tube, as compared to the regular tube.