International Journal of Scientific and Research Publications, Volume 3, Issue 11, November 2013 1 ISSN 2250-3153 www.ijsrp.org Double Diffusive Heat and Mass Transfer over a Vertical Plate in the Presence of Wall Suction and Chemical Reaction Mangwiro Magodora 1 , Kisswell Basira 2 , Precious Sibanda 3 1, 2 Department of Mathematics & Physics, Bindura University, P. Bag 1020, Bindura, Zimbabwe 3 School of Mathematical Sciences, University of KwaZulu-Natal, P. Bag X01, Pietermaritzburg, Scottsville 3209, South Africa Abstract- A steady incompressible boundary layer flow over a permeable vertical plate in the presence of a chemical reaction and wall suction is investigated. The governing fluid flow equations are transformed into a set of coupled ordinary differential equations with the help of similarity transformations and solved using asymptotic approximations in the presence of large buoyancy to obtain closed form solutions of the skin friction, Nusselt and Sherwood numbers. The effects of varying the buoyancy parameter on the velocity, concentration, temperature, skin friction and the rates of heat and mass transfer are determined and presented graphically, using MATLAB. Results indicate that an increase in buoyancy is accompanied by an increase in fluid velocity and a decrease in the fluid temperature and fluid concentration. Results also show that an increase in buoyancy is accompanied by an increase in skin friction, while the rates of heat and mass transfer fall rapidly from very large values close to the wall down to a minimum value and then start to increase as the buoyancy parameter becomes larger. It is also noticed that the increase of the rate of heat transfer is more pronounced than the rate of mass transfer as the buoyancy parameter is increased. Index Terms- Double Diffusive Convection, Mixed Convection, Boundary Layer, Buoyancy, Wall Suction, Skin Friction. Nomenclature a C constant concentration of chemical species Tw T∞ temperature at the plate surface free stream temperature Cw concentration at the plate surface u velocity component along x-direction C∞ D free stream concentration diffusion coefficient U∞ v free stream velocity velocity component along y-direction fw transpiration rate V0 (x) wall suction g acceleration due to gravity x coordinate directed upward along the plate Grx,c Grashof number due to concentration y coordinate directed normal to the plate Grx,t Grashof number due to concentration α thermal diffusivity kr chemical reaction rate constant βc volumetric-expansion coefficient due to concentration N buoyancy ratio βt volumetric-expansion coefficient due to temperature P r Prandtl number δ boundary layer thickness Rex Reynolds number ξ dimensionless buoyancy parameter Sc Schimdt number  ν dynamic viscosity T fluid temperature ψ stream function I. INTRODUCTION he phenomenon of heat and mass transfer, also referred to as double diffusive convection, has attracted extensive research interest due to its many applications in science, engineering and technology. Heat and mass transfer involve buoyancy driven flows induced by a combination of temperature and concentration gradients. Many transport processes occur in nature and industrial applications in which combined heat and mass transfer takes place simultaneously due to combined effects of thermal diffusion and diffusion of chemical species. The phenomenon of heat and mass transfer is encountered in chemical process industries such as polymer production and food processing as well as in other fields such as oceanography, geology, biology, astrophysics. Heat and mass transfer processes are also observed in buoyancy induced motions in the atmosphere and in bodies of water. Atmospheric flows are driven appreciably by both temperature and concentration gradients while flows in bodies of water are driven by equally important effects of temperature, concentration of dissolved materials and concentration of suspended particulate matter. The problem being investigated is a case of mixed convection, in which both free convection and forced convection are significantly present. Convective heat transfer is one of the T