Numerical study of natural convection drying of coffee grains contained in a vertical channel with constant heat flux on walls

SYNOPSIS

We present a numerical study of the drying by natural convection of coffee grains contained between two vertical walls subjected to a uniform heat flux. The coffee grains bed is assumed to be in a porous medium, heat and mass transfers which are described by the classical natural convection equations and the Darcy-Brinkman momentum equation. The discretisation of these equations by an implicit finite difference method leads to algebraic equations systems, which are solved by using the Gauss algorithm. The effect of aspect ratio (6 ≤ H ≤ 24), thermal Rayleigh number (0.5 ≤ Ra_T ≤ 2), mass Rayleigh number (5 ≤ Ra_c ≤ 25), Lewis number (1 ≤ Le ≤ 5) and Darcy numbers (10⁻³ ≤ Da ≤ 10₋₅) on the evolution of the drying is presented. The coffee grain diameter, the equivalent thermal conductivity of the porous medium, ambient temperature and hygrometry have been identified as parameters which greatly affect heat and mass transfers intensity during the drying.