Numerical simulation of critical heat flux in forced boiling of a flow in an inclined tube with different angles

Abstract

In this paper, the effect of changing tube slope on the critical heat flux for the evaporation of upward saturated flow of a liquid (water) in a near-vertical tube has been studied numerically. For this purpose, the effect of increasing the pipe slope and changing the wall temperature and the inlet fluid temperature on the volume fraction of vapor, heat transfer coefficient, heat flux and velocity profile is analyzed. In the most industrial units, boiling in diagonal channels is very important. Tube slope has an important effect on the flow stability. In practical applications, the existence of natural obstacles in the direction of transmission lines causes the orientation of these lines at different angles. The geometry of cases is a tube with 2.5 cm diameter and 100 cm length into which constant mass flow of fluid has been entered with rates of 0.05 kg s−1. Because of having no changes in the third direction, the problem has been modeled two-dimensionally. Numerical simulation of fluid was done by using the RPI subcategory of boiling from the Eulerian model, and the comparison of numerical results with valid experimental data shows 14% of error. The temperature difference range of 10 °C up to 330 °C has been applied to the tube wall. The outcome of this study was the increase in vapor volume fraction and heat flux and decrease in heat transfer coefficient with increasing the temperature difference. Increasing the tube slope causes an increase in vapor volume fraction, heat flux and velocity profile and reduction in the temperature of the occurrence of critical heat flux.