Transient conjugate mixed convection from a sphere in a porous medium saturated with cold pure or saline water

In this paper, a numerical investigation of the transient conjugate mixed c onvection flow about a sphere embedded in a porous medium saturated with pu re or saline water is carried out. The effect of density extremum is consid ered by using the nonlinear dependence of density on the temperature. The s alinity effects are considered by assuming uniform saline concentration ove r the domain considered. The direction of the natural convection is changed either to aiding or to opposing the upcoming flow direction simulating the sphere is either hot or cold relative to the surrounding temperature. Resu lts show that the initial temperature differences as well as the saline con centration alter the transient heat transfer rate in conceivable degree. It was found that the heat capacity ratio between the sphere and the surround ing media has more significant effect on the calculated heat transfer rate than the thermal conductivity ratio. The study is performed by using six no ndimensional parameters and results are discussed in detail.