Computational Modelling of the Transport Phenomenons During Low Temperature In-Bin Drying and Aeration of Amaranth Grains

Abstract

In the present work a full model for the in-bin low-temperature drying of amaranth grains based on the finite elements method (FEM) was developed, taking into account re-analyzed specific relationships developed in previous works for description of properties of grains, drying kinetic and equilibrium moisture content. Due to the nature and symmetry of the problem of in-bin drying and aeration of amaranth grains, FEM model was performed considering a one-dimensional domain. The discretization was made through a structured mesh density having 96 Lagrange quadratic elements.
Coupled One-Dimensional Transport Equations for Moisture Mass, Heat and Momentum Transfer in both phases (solid and gas) were planned and solved using the following Application Modes of COMSOL Multiphysics. 3.5a: transient analysis of Convection and Diffusion (for air and grain) from Multiphysics Module; transient analysis of General Heat Transfer (for air and grain) from the Heat Transfer Module; and state analysis of fluid flow with Darcy´s Law (for air) from the Earth Science Module. The grain bed was considered unique-like material with effective properties (i.e., diffusivity, permeability). Experimental data and relationships of thermo-physical properties, equilibrium moisture content, heat of sorption, drying kinetics and resistance to airflow determined in previous works were used to define the Constants, Scalar and Global Expressions in the definition of the COMSOL FEM model. Voids fractions and superficial velocities were specified, and pressure-drops through the grain bed, and rates of heat and mass transfer from the kernels to the air, were determined. The simulations of the FEM model provided useful information about temporal and spatial moisture content in the deep bed of amaranth grains.