Numerical Simulation of Heat and Mass Transfers During Solar Drying of Sewage Sludge: Solar Radiation Effect

Abstract

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 transfers during 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 transfers in the channel and the porous medium are respectively described by the classic equations of forced convection and 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 on the space-time evolution of temperature, velocity and mass fraction at the porous medium-fluid interface. Moreover, the evolutions of the Nusselt numbers are represented to characterize the transfers at the sludge surface. This work is completed by a drying kinetics study. Indeed, we represent the effect of solar radiation on the space-time evolution of the drying rate.