Modelling for vacuum drying characteristics of coconut presscake

Coconut presscake is a by-product obtained after extraction of coconut milk from coconut meat. The initial moisture content of coconut presscake is approximately 1.038 ± 0.029 kg water kg dry solid−1 and this has to be reduced to below 0.03 kg water kg dry solid−1 having about 0.75 water activity for its long term storage and convenience. In the present work, coconut presscake was dried in a laboratory scale vacuum dryer to moisture content less than 0.02 kg water kg dry solid−1. Drying characteristics of the presscake was investigated under varying conditions of presscake thickness (2, 3 and 4 mm) and vacuum chamber plate temperature (65, 70 and 75 °C) at 65 mm Hg absolute pressure. Different drying models were used to simulate the observed drying data. Based on the consideration of reduced moisture diffusivity at low moisture a new model was proposed, which was found to give better predictions than the other models. The relative deviation percent between the actual and predicted moisture ratios at different drying time for this model was in the range of 3–15%. Effective moisture diffusivity, computed on the basis of Fick’s law varied between 7.026 × 10−10 and 3.326 × 10−9 m2 s−1. The temperature and thickness dependence of effective moisture diffusivity was expressed by an Arrhenius type equation.