Comparative Energy and Exergy Analyses of Single-Mode and Combined Drying Methods for Orange-Fleshed Sweet Potato

Abstract

Orange-fleshed sweet potato is valued for its high β-carotene content, a precursor of vitamin A. It is a highly perishable storage root due to its high moisture content, which contributes to rapid deterioration after harvesting. Therefore, it requires drying for preservation and value addition. Drying is one of the most energy-intensive operations in food processing. However, the comparative thermodynamic performance of single-mode and combined drying methods for orange-fleshed sweet potato has not been established. Hence, this study aimed to evaluate and compare the energy and exergy performance of single-mode and combined dryer configurations. These include convective hot air (CH), infrared (IR), microwave (MW), and four hybrid combinations, namely, CH-IR, CH-MW, IR-MW, and CH-IR-MW. This was further evaluated across three orange-fleshed sweet potato varieties and blanching pre-drying treatment. The specific energy consumption, drying process efficiency, dryer efficiency, energy utilization, exergy efficiency, and improvement potential were determined from thermodynamic models based on the first- and second-laws of thermodynamics, rather than from directly measured total electric energy. IR-MW (3.01–3.99 MJ.kg−1) and MW (2.58–4.59 MJ.kg−1) achieved the lowest specific energy consumption, which was up to 98.3% lower than CH drying (44.14–66.61 MJ.kg−1). CH-IR-MW had the highest process efficiency (24.77%), dryer efficiency (87.66%), and exergy efficiency (26.30%). Although IR-MW and CH-IR-MW achieved the highest energy and exergy efficiency, CH-IR and CH-MW exhibited the greatest potential for exergetic improvement. These findings identify IR-MW and CH-IR-MW as the most energy- and exergy-efficient drying methods for orange-fleshed sweet potato, providing a practical basis for drying technology selection.