A fully elliptic numerical study is performed to investigate the buoyancy-affected, three-dimensional laminar flow and heat transfer in the entrance region of a helical pipe at a constant wall temperature. The Control Volume Method with second-order accuracy is used to numerically solve the three-dimensional fully elliptic governing equations for the problem. The O-type non-uniform structure grid system is adopted to discretize the computation domain (two complete turns of a helical pipe) in this study. The Bossinesq approximation is applied to deal with the buoyancy effect caused directly by density difference. The developments of flow and temperature fields, profiles and characteristics at different Gr/Re2 are given and discussed. The computed results reveal that the entrance region of heat transfer is increased rapidly when buoyancy force is considered. In the meantime, the buoyancy effect on the average Nusselt number and friction factor is greater at the entrance region of the helical pipe, but it gradually becomes weaker further downstream.
