Abstract

A conductive rotary dryer was developed for indirect drying of cassava meal in gari and cassava flour production. Drum temperature, T_d, batch quantity, Q_b and vapour extraction rate, R_v, of the dryer influenced drying kinetics of cassava meal. Drying data of cassava meal under different dryer conditions were fitted with seven thin-layer drying models and the Logarithmic model had the best goodness of fit with R²˃0.97 for each of the parameters. Model constants, a, k and c were generated as functions of each parameter and three Logarithmic models relating moisture ratio, MR as a function of each parameter were developed. Predicted and experimental values of MR correlated well at R²˃0.97 for each model. Gradients of drying curves of moisture loss, ML, against drying time, t, were linear between t = 0 and a critical time t_c when drying actually stopped. A mathematical model based on the linearity of drying rate, DR, was developed to predict MR as function of T_d, Q_b, R^v and t. The model was validated by comparing experimental and predicted values of MR at various combinations of dryer parameters. Drum temperature and batch quantity had greater effects on drying kinetics than vapour extraction rate. At T_d = 200°C the cassava meal was gelatinized and gari with swelling index, SI>2.0 was produced. Cassava flour with SI<2.0 was produced at T_d = 140°C.

Keywords:

Cassava, flour, gari, indirect drying, model,

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