Laminar flow heat transfer for asymmetrical non-uniform heat flux distributions on horizontal circular tubes

Abstract

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.

In this study, the influence of symmetrical and asymmetrical non-uniform heat flux distribution boundaries in terms of the gravitational field on the internal heat transfer coefficient and the friction factor in a horizontal circular tube was investigated numerically. Of interest was buoyancy driven flow in the laminar flow regime. Inlet fluid temperature and external loss convective heat transfer was also considered. Three-dimensional steady-state numerical simulations were performed using ANSYS Fluent version 14. Circumferential non-uniform heat flux was simulated as a sinusoidal function of the heat flux incident on the tube. A steel tube was considered which had a wall thickness of 5.2 mm, a length-to-inner-diameter ratio of 160, and a thermal conductivity of 16.27 W/mK. The results showed that the average internal heat transfer coefficients and friction factors for the symmetrical non-uniform heat flux distribution cases were higher than that of the asymmetrical case considered. The heat transfer coefficient also increased with an increase in the inlet fluid temperature for the uniform heat flux, symmetrical and asymmetrical nonuniform heat flux distributions cases. However, the average internal heat transfer coefficient decreased with the increase in the external loss convective heat transfer coefficient. It was found that the friction factor decreased with increase in the fluid inlet temperature and external loss convective heat transfer coefficient for the uniform heat flux, symmetrical and asymmetrical non-uniform heat flux distributions cases.