Modelling of moisture diffusivity during solar drying of locust beans with thermal storage material under forced and natural convection mode

Abstract

This study investigated the modelling of moisture diffusivity of processed locust beans under forced and natural convection mode using solar drying with thermal storage materials (gravel). The experimental data obtained were fitted into eleven existing thin layer models and the best model choice was based on a comparison of statistical parameters including determination coefficient (R2), reduced chi-square (ᵪ2), root mean square error (RMSE), square error sum (SSE) and normalised root mean square error (NRMSE) between the experimental and predicted data. The results showed that the Lewis model gave the best description of solar drying of locust beans under forced and natural convection mode. Thus, this model may be adjudged to represent the drying characteristics of locust beans in a thin layer within the experimental range of study. The obtained moisture diffusivity values were 2.73496 and 1.82331 × 10-11 m2/s for the solar drying of locust beans under forced and natural convection mode respectively. The predicted Arrhenius constant and activation energy values were respectively 2.54 × 10-11 m2/s and 21.65 kJ/mol. Keywords: Modelling, Moisture diffusivity, Solar drying, Locust beans, Thermal storage material, Forced and natural convection