Analysis of the efficiency of the geothermal dryer and its effect on the kinetic mass transfer parameters

Abstract

Geothermal energy is an efficient alternative for convective drying of food. This research aimed to determine the efficiency of a low-temperature geothermal dryer (LTGE) system in dehydrating high-moisture foods and its effects on the kinetic parameters and properties of the dehydrated foods. This study used a prototype laboratory-scale geothermal dehydrator built at the Geothermal Laboratory of the Engineering Institute of UNAM. The influence of the geothermal dehydrator operating parameters- average temperature (60, 65, 70 °C) and airflow velocity (2.5, 3.0, 3.3 m/s) on moisture content kinetics, drying rate, moisture-effective diffusion coefficient (Deff), physicochemical properties, and drying efficiency was determined. The results indicated that mean temperature and airflow rate influenced the drying kinetics and properties of dried apples and mangoes. With increasing temperature and airflow velocity, the drying rate and effective diffusion coefficient increased. The drying curves were dominated by the period of decreasing rate, which is typical of the drying kinetics of biological materials under constant-temperature conditions. The increase in temperature and airflow velocity increased the effective diffusion coefficient and drying efficiency. The Deff ranged from 0.43–8.59 x 10–9 m2/s for the dried apple samples and from 5.54–8.92 x 10–9 m2/s for the dehydrated mango samples. Moisture content curves showed moisture contents below 10% at drying times similar to those achieved with a conventional convective dryer, demonstrating that geothermal energy can be used for fruit dehydration, producing high-quality dehydrated products and enabling efficient drying processes.