Pilot-Scale Radio Frequency Drying of Macadamia Nuts: Heating and Drying Uniformity

Abstract

Hot air assisted radio frequency (HARF) heating holds potential to provide fast drying of Macadamia nuts with acceptable product quality. The goal of this study was to determine heating and drying uniformity of Macadamia nuts in a pilot-scale 27.12 MHz, 6 kW radio frequency (RF) system as influenced by container locations in the RF chamber, moving conditions, and with or without additional hot-air heating. Uniformity index values estimated by measured sample temperatures and weight changes over 12 compartments in the container were used for comparing heating and drying uniformity, respectively, between HARF- and RF-only treatments. Experimental results showed central heating in the HARF-treated four-layer tray and edge or corner heating in RF-alone-treated Macadamia nuts. Moving samples did not clearly improve heating and drying uniformity. The RF uniform drying was achieved with applied hot-air surface heating based on relatively small weight changes over 12 compartments in the container. The determined HARF heating and drying conditions are useful for further industrial applications.