The effects of natural convection on the simultaneously developing laminar flow inside a uniformly heated inclined tube have been numerically studied using the three-dimensional parabolic formulation and the SIMPLE-C algorithm. It has been observed that the buoyancy-induced secondary flow develops quite rapidly, drastically perturbing the flow and thermal field. Its intensity increases to a maximum and then decreases to a certain asymptotic state as the fully developed conditions occur. The axisymmetry of the flow and the thermal field is destroyed. The isotherms are considerably distorted because of the strong stratification inside the fluid due to the secondary flow. Such effects increase appreciably with increasing Grashof number but tend to decrease as the tube inclination increases. The point of the maximum axial velocity is located on the diameter q = 0, p and well below the tube axis for horizontal tubes. This point moves upward for the case of inclined tubes. It has been generally, found that buoyancy forces enhance appreciably the wall shear stress, as well as the heat transfer to the fluid. The average wall shear stress increases considerably with increasing tube inclination. The asymptotic Nusselt number depends strongly on the tube inclination.

Units: Dual