A proposed mathematical model, based on physical and transport properties and mass and energy balances, was developed for unsteady transport of momentum, heat and mass in granular beds of agricultural products (fruits and vegetables) under convective drying conditions. The model utilized water sorption isotherm equations and the change in solid density due to shrinkage. The unsteady‐state differential equations for temperature and moisture profiles within the product were numerically solved using a central finite difference scheme. Experimental data on drying conditions and product drying rates agreed with the calculated results. A design and operation parameters optimization scheme, tested for grapes, resulted in minimized drying time and high quality dried product.
This work focused on the numerical study of the thermal performance of a solar collector in order to improve the indirect solar drying of fruit in an environment with high solar potential. It aims to contribute to the reduction of post-harvest losses observed during periods of high production. From the retained physical model, an equivalent electrical scheme has been established and energy balance was applied to each slice of the model using the nodal method. The obtained different equations were discretized using the implicit method of finite differences, and solved by the iterative Gaussian Pivot method written in FORTRAN program. The obtained results showed that, from April to June (mangoes harvest period in Ngaoundere city) the raining period in Adamawa Region, the solar air collector that length to width ratio is between 2 and 3, is sufficient to carry out indirect solar drying of fruits with forced convection. The outlet air temperature of the solar collector was between 45 and 60°C with an average value of 50°C, and the thermal efficiency was between 65 and 95% with an average value of 80%. Double glazing improves efficiency of the solar air collector for a small footprint.
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