Transport phenomena, thermodynamic analyses, and mathematical modelling of okra convective cabinet-tray drying at different drying conditions

Abstract

Okra is a vegetable that is highly consumed for its nutritive and health benefits. Due to its highly perishable nature, it is often subjected to hot air drying to increase the shelf-life. Hence, the drying kinetics, moisture diffusivity, heat and mass transfer coefficient, total and specific energy consumption, and exergy (exergetic efficiency, exergetic improvement potential rate, and exergetic sustainability index) are essential parameters required for the drying system design. This study was therefore focused on okra drying data generation for the determination and evaluation of these parameters. The major goal was to utilize the generated data for the development of an innovative process model that can find application in dryer design. A self-designed laboratory cabinet-tray dryer was used for the drying at different drying conditions (temperature (40-70 oC), air velocity (0.5-2.0 m/s), and relative humidity (60-75%)). The obtained results showed that the effective moisture diffusivity ranged from 2.59×10-10 - 7.50×10-10 m2/s while the heat and mass transfer coefficient varied from 1.24-8.07 W/m2K and 1.61×10-7-18.3×10-7 m/s over the drying conditions range, respectively. The energy consumption increased with increasing air velocity, temperature, and relative humidity. The exergy loss rate was higher at higher air velocity, temperature, and relative humidity. The energy and exergetic efficiencies respectively varied from 0.78-4.67% and 65.12-84.96% over the drying conditions range. The exergetic improvement potential rate and the exergetic sustainability index of the drying chamber varied from 0.013-0.201 kW and 2.86-6.65, respectively. An innovative multiple linear regression-Biot-Lag factor model was developed.

Keywords

• bi-g model
• drying conditions
• energy and exergy analyses
• moisture diffusivity
• multiple linear regression model
• okra drying