Moisture Diffusivity and Activation Energy of an Improved Variety of Cowpea as affected by period of harvest and drying conditions

Abstract

Field drying is commonly used for drying cowpea in Nigeria but, it has a main disadvantage of slow drying rate. In this investigation, thin layer drying behaviour of IT 97K 56S IS was studied. Experiments were performed on samples harvested 60, 64, 68 and 72 Days After Planting (DAP) and drying temperature of 55, 65, 75 and 85ºC was used with a convective dryer. Effective moisture diffusivities of IT 97K 56S IS were determined by applying Fick’s second law of diffusion and the Activation energy was also determined. The results showed that all drying experiments had only falling rate periods and the temperature dependence of the effective moisture diffusivity followed an Arrhenius type relationship. Effective moisture diffusivity varied from 1.4121 6.8322 × 10 9 m/s while the activation energy were between 30.70 46.08 kJ/mol indicating drying of the cowpea variety requires a relatively minima energy for all the periods of harvest. The higher the temperature, the higher the effective moisture diffusivity and the longer the period of harvest, the higher the activation energy