Combined heat and mass transfer in natural convection along a vertical cylinder

Abstract

An analytical study is performed to examine the heat- and mass-transfer characteristics of natural convection flow along a vertical cylinder under the combined buoyancy force effects of thermal and species diffusion. The analysis is restricted to processes in which the diffusion-thermo and thermo-diffusion effects as well as the interfacial velocities arising from species diffusion are negligible. The surface of the cylinder is either maintained at a uniform temperature/concentration or subjected to a uniform heat/mass flux. Among the major parameters of the problem are curvature of cylinder, Prandtl and Schmidt numbers, thermal and concentration Grashof numbers, and the relative buoyancy force effect between species and thermal diffusion. Numerical results are obtained and presented for species diffusion of interest in air and water. For both heating/diffusing conditions, the local wall shear stress, the local Nusselt number, and the local Sherwood number increase with increasing curvature of the cylinder. In addition, the first two quantities are found to increase and decrease as the buoyancy force from species diffusion assists and opposes, respectively, the thermal buoyancy force. The mass-transfer parameter or the local Sherwood number is enhanced as the thermal buoyancy force increases. Finally, the combined buoyancy force from thermal and species diffusion provides larger Nusselt and Sherwood numbers for uniform surface heat/mass flux than for uniform wall temperature/concentration.