A Theoretical study has been conducted on the influence of Semi-tube orientation on combined free and forced laminar convection heat transfer where the Semi-tube heated with constant surface temperature. The theoretical study was done for both the thermal entrance region and hydraulically fully developed region.
Theoretically the governing equations for a flow through an inclined Semi-tube were reduced to four, which are continuity equation, radial and tangential momentum equations, axial momentum equation and vorticity equation in which the variables where the temperature, vorticity, stream function and axial velocity. These equations were reduced to dimensionless equations in which Grashof, Prandtl, Reynolds and Rayleigh numbers were presented. These equations were numerically solved by using the marching process explicit finite difference method and Gauss elimination technique. Numerical results for the inclined Semi-tube heated by constant surface temperature in the thermal entrance region were obtained and represented by stream function contours and isotherms for different values of Rayleigh and channel angle, as well as the circumferential distribution of local Nusselt number and the change of average Nusselt number with Rayleigh number. The results clarify the significant effects of the secondary flow created by natural convection on the heat transfer process, reveal an increase in the Nusselt number as the angle of inclination moves from the vertical to the horizontal position.