Natural Convection Heat and Mass Transfer in the Boundary Layer along a Vertical Cylinder with Opposing Buoyancies

Abstract

The effects of opposing buoyancies on natural convection heat and mass transfer in the boundary layer over a vertical cylinder immersed in a quiescent Newtonian fluid are presented in this paper. The surface of the cylinder is maintained at a constant temperature and concentration. The homotopic transformation is proposed to transform the physical domain into a flat plate. The boundary layer equations and the boundary conditions are solved numerically using an implicit finite difference scheme and the Gauss-Seidel algorithm. The buoyancy ratio N, Prandtl number Pr and Schmidt number Sc are important parameters for this problem. The numerical results for Pr=Sc and Pr≠ Sc, including the velocity, temperature, concentration fields and the Nusselt number as well as the Sherwood number along the surface of the cylinder are discussed for aiding and opposing buoyancies. Results show that the Nusselt (Sherwood) number increases with positive or negative buoyancies ration N (N=Grc/Grt). Moreover, for opposing flows with Sc<Pr , the flow is completely downward, the thickness of the concentration layer is larger than that of the thermal layer . For Pr<Sc , the velocity are weak and the thermal layer thickness is much larger.

Keywords

• Free convection
• Boundary layer
• Buoyancy force
• Vertical cylinder
• Heat transfer
• Mass transfer