Convective heat transfer in a porous medium downstream of a sudden expansio

Mixed convection in a horizontal porous duct with a sudden expansion of its cross-sectional area has been investigated numerically and experimentally. A heat source with its length equal to the duct height after the expansion is located at the bottom wall in the adjacent wake of the step.;The governing differential equations are solved by using a finite different method. Calculations have been carried out with Darcy's law, and both isothermal and constant-flux heating cases are considered. It is found that the Nusselt number monotonically increases with the Peclet number at low Rayleigh numbers, and has a critical Peclet number at which the Nusselt number is minimum at large Rayleigh numbers. The calculations with various expansion ratios of flow area demonstrate that the step height has little effect on the heat transfer characteristics if the Peclet number is defined based on the average flow velocity at the exit.;Experiments have been conducted to verify the numerical results with a constant-flux heat source and the step height half of the duct height after the expansion. It is observed that the numerical results agree well with the experimental results, and several findings in the numerical study on local and overall heat transfer characteristics are confirmed.;Correlations to describe the overall heat transfer characteristics have been obtained based on both numerical and experimental results through non-linear regression analysis. For the range of parameters employed in the present study, the results are well correlated by the same parameter groups and formulation used in a previous study which investigated mixed convection in a horizontal porous layer without a step. It is found that the correlation for Nusselt number as a function of Rayleigh and Peclet numbers obtained in the present study is very close to that in the case without a step, and it is concluded that the existence of the step has little effect on the mixed convection heat transfer coefficients in a horizontal porous layer.