Comparative evaluation of hybrid drying techniques for orange fleshed sweet potato: Drying kinetics, quality, thermodynamic analysis, and computational fluid dynamics

Title : Comparative evaluation of hybrid drying techniques for orange fleshed sweet potato: Drying kinetics, quality, thermodynamic analysis, and computational fluid dynamics

Abstract:

Conventional hot-air drying is widely recognised as a slow process that often compromises product quality and consumes a significant amount of energy. This study compared single and hybrid drying methods, consisting of Convective Hot-air (CH), Infrared (IR), and Microwave (MW) drying to determine their effects on the drying characteristics of orange fleshed sweet potato (OFSP). Three OFSP varieties (Beauregard, Bophelo, and W-119) were investigated with and without blanching pre-drying treatment using a randomized complete block experimental design. Moisture ratio (MR), drying rate (DR), effective moisture diffusivity (D_eff), activation energy (E_a), colour parameters (L^*, a^*, b^*, ∆E), β-carotene retention, mineral composition and microstructure changes were analysed. Among all the drying methods investigated, CH-IR-MW drying reduced the drying time by 85-98%, achieved the highest DR (0.06 kg.min^-1), highest D_eff (2.79×10^-9 m².s^-1) and lowest specific energy consumption (SEC) of 0.026 MJ.kg^-1. It also resulted in lower colour changes (∆E= 4.81-19.54), better granule integrity and the highest β-carotene retention (91.56%). Blanching increased DR and D_eff of OFSP slices relative to control samples. Mineral analysis identified Carbon and Oxygen as dominant elements, with certain minerals concentrating as moisture was being removed. Among eleven mathematical models evaluated, the Demir et al., Jenas and Das and Page models most accurately predicted the MR (R² values > 0.99, low RMSE and ꭓ²). Overall, integrating the IR surface heating method with MW volumetric heating, under moderate hot-air temperatures of CH, effectively shortens the drying time, reduces energy use, and preserves the quality of OFSP. Furthermore, Computational Fluid Dynamics simulations were undertaken to analyse the airflow patterns, temperature distribution and the moisture transfer during CH-IR-MW drying. These tools will support the optimization of the dryer geometry, operating conditions and energy efficiency. In conclusion, combining drying techniques significantly improves drying performance and the thermodynamic and CFD analyses provides insight for designing efficient hybrid dryers for OFSP flour production.

Biography:

Khuthadzo Mugodo is a candidate Agricultural Engineer registered with ECSA and has over 12 years of professional experience. She is a lecturer in Agricultural Engineering at the University of KwaZulu-Natal and is currently pursuing a PhD in Engineering. Her research focuses on food process engineering technologies and renewable energy integration. She began her career at the Agricultural Research Council, contributing to post-harvest technology and rural infrastructure projects. Khuthadzo teaches Engineering Design and Undergraduate Seminar, has published in peer-reviewed journals, and presented internationally, including at AgEng 2024 in Athens. She also co-hosts the Agricultural Engineering Podcast and has participated in prestigious international fellowship and training programmes.