NUMERICAL MODELING OF HEAT AND MASS TRANSFERS UNDER SOLAR DRYING OF SEWAGE SLUDGE

The drying of sewage sludge is a current environmental problem, not sufficiently described in the literature. Hence, the aim of this work is a numerical study of heat and mass transfer under solar drying of residual sludge. This sludge is assimilated to a porous medium and exposed to a forced convection laminar flow within a horizontal channel. The processes of transfer in the channel and in the porous medium are respectively described by the classical equations of forced convection and of the Darcy-Brinkman-forchheimer model. The implicit finite difference method is used to discretize the governing differential equation system. The algebraic systems obtained are solved using the Gauss, Thomas, and Gauss-Seidel algorithms. To determine the drying rate, we associate a drying kinetics model. We particularly studied the effects of solar radiation intensity and ambient air temperature on the space-time evolution of temperature, velocity, and mass traction at the ambient air-porous medium interface. Moreover, the evolutions of Nusselt and Sherwood numbers are represented to characterize the processes of transfer at the sludge surface. This work is completed by a drying kinetics study. Indeed, we represent the space-time evolution of the drying rate and water content.