Design and Development of a Desiccant Assisted Microwave–Convection Food Drye

Abstract

30% of the world’s agricultural production is lost in post-harvest stage due to the perishability of agricultural food items. To alleviate this problem, food can be dried to prolong its shelf life. However, there is a trade-off between product quality and energy cost for most dehydration methods. The objective of this study was to develop a food drying method that could deliver product quality that was competitive with highly eco-hazardous and energy intensive methods while being more energy efficient. To meet this objective, a solar thermal regenerated liquid desiccant dehumidification system was designed and manufactured. It was connected to a Microwave-Convection heating chamber to house the food items to be dried. To reduce energy consumption even further, it was theorized that instead of operating the Desiccant-Microwave Convection drying process consistently, the process could be divided into three stages; starting with high temperature Convection drying, followed by Microwave-Convection drying at a reduced temperature, followed by Desiccant assisted Convection drying at an even lower temperature. The Desiccant-Microwave-Convection dryer was experimentally tested to dry potato slices. The combined process delivered 81.6% shorter drying time compared to Convective Drying and 27.8% shorter drying time compared to Microwave Drying. The process was also found to consume 66.1%, 10% and 5% lower energy compared to Convective Drying, Microwave drying and combined Microwave-Convection drying respectively. It was also found to retain 87.8% of the original food’s color. When the process was divided into three stages with sequentially reducing temperatures, the cascaded configuration resulted in 22.2% reduction in energy consumption compared to using Desiccant-Microwave-Convection drying continuously and preserved 92.5% of the potatoes’ original color, which is comparable to Freeze Drying. The findings of this study are encouraging and can be used to further develop desiccant based hybrid drying techniques for a range of food items