Thermal Diffusivity Measurements of Apples by Microwave Radiation

A microwave generator and a closed-circuit wind tunnel were used to measure the thermal diffusivity of four varieties of apples (Malus pumila (Mill.)) by the non-steadystate method. The coefficient of variation for the measurements of thermal diffusivity of apples did not exceed 5.8% as determined through the analyses of the cooling curves. The method is relatively rapid as a single measurement of thermal diffusivity was completed within two hours. Thermal diffusivities for the post-harvest apples ranged from 1.22 x 10-7 m2s-1 for Atlas to 1.47x 107m2s-1 for Cortland. The use of a semi-empirical relationship based on fruit moisture content and temperature range was found insufficient to fully account for the variation in the thermal diffusivity values of apples observed in the present study.