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.
