A forced convection automatic cabinet dryer integrated with a data logger was designed and fabricated. The okra samples were dried in the dryer at drying temperatures of 50, 60, and 70 °C and at three different load densities of 200, 300, and 400 g at a continuous air velocity of 0.7 m·s^–1. Energy and exergy analyses of the drying process were performed. The obtained results showed that the energy efficiency, energy utilisation, and utilisation ratio increased from 26.59 to 68.24%, 5.47 to 114.36 W, and 0.36 to 0.71 as the temperature increased to 70 °C, respectively. The inflow, outflow, and exergy losses were in the range of 7.02 to 26.14 W, 4.43 to 14.16 W, and 2.59 to 11.98 W, respectively, while exergy efficiency varied from 49.15 to 63.47%. The findings show that exergy efficiencies decrease with an increase in the drying temperature, but increase with a lower load rate. The index of sustainability varies from 2.14 to 2.77, the value increases as the load density decreases while it decreases with a temperature increment.

In this study, drying characteristics, kinetic modelling, energy and exergy analyses of a convective hot air dryer are presented for water yam. The drying experiments were carried out at temperature levels of 50, 60, and 70°C and slice thicknesses of 3, 6, and 9 mm. The effects of drying variables on the drying rate (DR), moisture diffusivity (Deff), activation energy (Ea), energy utilization (EU), energy utilization ratio (EUR), exergy loss (EXL), exergy efficiency (EXeff), improvement potential (IP), and exergetic sustainability index (ESI) were investigated. The results showed that increasing air temperature increased the DR, Deff, EU, EUR, EXL, EXeff, IP, and ESI, while increasing the slice thickness increased Deff and Ea, but decreased the DR. The highest Deff and Ea values were 4.2 × 10−8 m2/s, and 53 KJ/mol, respectively. EU and EUR varied from 10 to 150 J/s and 0.39 to 0.79, respectively. EXL and EXeff varied between 2 and 12.5 J/s and 58 to 75 %, respectively. Midilli’s model had the best performance in predicting the moisture ratio of water yam with coefficient of determination (R2 = 0.9998), root mean square error (RMSE = 0.0049), and sum of square error (SSE = 0.0023).

Drying is one of the major unit operation in food industry and it kinetics data is required for optimization. The aim of this study was to evaluate the effect of air temperature (50, 60, and 70°C), air velocity (0.5, 1, and 1.5 m/s), and slice thickness (3, 6, and 9 mm) on the moisture ratio of yam slice during drying. Ten (10) different empirical models were used in fitting the experimental moisture ratio data, the prediction performance was evaluated with sum of square error (SSE), coefficient of determination (R2) and root mean square error (RMSE). The model fitting shows that the Two term model was most performed based on R2, SSE, and RMSE value. This result can be use to control the drying systems for yam slice.