The effects of exponentially varying viscosity and linearly varying thermal conductivity on unsteady MHD natural convective flow past a semi infinite vertical plate in a thermally stratified medium is studied. The variables of both viscosity and thermal conductivity are considered only a function of temperature. The governing boundary layer equations of continuity, momentum and energy have been transformed into dimensionless coupled and nonlinear equations and after that solved by implicit finite-difference method of Crank-Nicolson type. The effects of the varying viscosity, thermal conductivity and stratification parameter at various times are discussed with velocity and temperature profiles and additionally the skin-friction and the rate of heat transfer.
KeywordsUnsteady, vertical plate, variable viscosity, thermal conductivity, thermal stratification.
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INTRODUCTIONFree convection flows are of great interest in a number of industrial applications, for example, geothermal frameworks, fiber and granular insulation etc. Buoyancy is also of importance in an environment where differences between land and air temperatures can give rise to complicated flow patterns. Heat transfer on fluid flow due to free convection in the presence of magnetic field finds subsidiary applications in different branches of Science and Technology such as atomic science, fire engineering, computational astrophysics, the magnetic behavior of plasmas in fusion reactors, liquid-metal cooling of nuclear reactors and electromagnetic casting. The problem of free convection flow past an infinite vertical plate under different plate conditions was studied by numerous researchers. Soundalgekar [1] studied the free convection effects on the Stokes problem for an infinite vertical plate by using Laplace transform method. Hellums and Churchill [2] were the first to present unsteady natural convective flow past a semi-infinite isothermal vertical plate by using an explicit finite-difference scheme. As explicit finite-difference scheme has its own particular lacks, later, Soundalgekar and Ganesan [3] have solved free convection flow past a vertical plate with mass transfer using implicit finite difference method of Crank-Nicolson type which is unconditionally stable and convergent.