Convective and microwave drying kinetics of white cabbage (Brassica oleracae var capitata L.): Mathematical modelling, thermodynamic properties, energy consumption and reconstitution kinetics

Abstract

The increasing cost of energy and low cost of white cabbage (WC) has made storage of white cabbage in cold storage room capital intensive, thus alternative and sustainable preservation methods are being sought. To adopt drying as a sustainable preservation method for WC, study of the heat transfer processes and energy use is very essential. This study presents the results of the drying kinetics, thermodynamic properties and energy consumption kinetics during drying of WC in hot air oven dryer (HAD) and microwave dryer (MD), as well as the reconstitution kinetics of WC. The results showed that both samples dried under a single rate drying period. The effective moisture diffusivity of HAD and MD ranges from 3.26 ×10−9to 6.07×10−9m2s−1 and 1.23×10−8 to 4.02×10−8m2/s, respectively. The activation energy of the samples dried in HAD and MD is 28.59933 kJmol−1K−1 and 10.026 J/g s−1, respectively. The specific energy consumption (SEC) was higher at the lowest drying temperature and microwave power level. SEC kinetic study revealed higher SEC at lower drying temperature and microwave power, and was intense right from the beginning of the drying process. Luka et al. model proved more appropriate in simulating the drying kinetic of WC. Thermodynamic analysis of the dryers revealed that the drying process was endergonic and endothermic. Drying methods and water temperature influenced the rate of reconstitution of WC.