Numerical Simulation Of Laminar And Turbulent Flow And Heat Transfer With Buoyancy

Numerical analyses have been conducted for combined heat and mass transfer by natural convection on a vertical surface, mixed free and forced laminar convection in vertical annuli and heat buoyancy effect on turbulence between two vertical parallel plates. The heat and mass transfer with heat and mass buoyancies and the fluid flow and heat transfer with heat buoyancy in laminar and turbulent flow have been investigated. The results obtained as follows:For natural convection on a vertical plate, velocity, heat and mass transfer rates decrease with the buoyancy radio B decreasing from high positive values, and then increase again with the buoyancy radio further decreasing after the velocity and transfer rates reaching a minimum. The value of buoyancy radio Bmin, at which the minimum Nusselt and Sherwood numbers are attained, is a function of Pr/Sc. If Pr/Sc<\, 5min<-l; contrarily, if Pr/Sc>1, 5min>-1; if Pr/Sc=1, then 5min=-1 and the Nu and Sh numbers are equal.For mixed free and forced laminar convection in vertical annuli, both the Nu number and the wall friction coefficient are higher than that of pure forced convection and increase with increasing Gr/Rein the buoyancy-aided flow, the heat transfer is then enhanced. In the buoyancy-opposed flow, the Nu number and the wall friction coefficient are less than that of pure forced convection and decreasewith increasing |Cr/Re|, and the heat transfer is then weakened. The reverse flow appears near the heated wall with higher heat buoyancy, the region of reverse flow is shown in the coordinate of Z/Pe- |Gr/Re|. The hydrodynamic and thermal entrance lengths increase with increasing |Gr/Re|. For mixed turbulent convection between vertical plates, the laminarization takesplace when Gr/Re3 <5× 10-5 in aided flow, then, the Nu number is lower than that of pure forced convection and it reaches minimum at Gr/Re3 = 2 × 10-5. The Nu number decreases with decreasing Gr/Re3 when Gr/Re3 <2 × 10-5 ; if Gr/Re3 > 2× 10-5 the Nu number increases with increasing Gr / Re3 number. The Nu number is higher and the wall friction coefficient is lower in opposed flow than those in aided flow. Opposed flow has less thermal entrance length than aided flow.