A mathematical model for predicting the drying rate of cocoa bean (Theobroma cacao L.) in a hot air dryer using dimensional analysis

Abstract

Development of a mathematical model for predicting the drying rate of a thin layer cocoa bean in a convective hot air dryer using dimensional analysis based on the Buckingham’s π theorem is presented. Results obtained show that drying rate decreases as the moisture level reduces due to increase in the intra-particle resistance to internal moisture migration of the cocoa beans. High coefficients of determination of 94.7%, 94.7% and 99.5% at temperatures of 60, 70 and 80^oC respectively between the predicted and experimental values showed that the method is good. The model was validated with data obtained from an existing thin layer convective dryer and there was no significant difference between the experimental drying rate and the predicted values at 5% level of significance. The results obtained from two-tail test indicate that t-calculated is less than t-tabulated at 5% degree of freedom indicating the suitability of the model at the studied temperatures. It was generally observed that drying cocoa bean at increasing drying temperature and decreasing moisture contents at constant air velocity result in low drying rate.