Experimental investigation of radio frequency heating uniformity of wheat flour surrounded by deionized water and NaCl solution

Abstract

The present study proposes an approach to overcome the problem of corner/edge overheating of foods undergoing radio frequency heating. For testing, a container with a central rectangular compartment surrounded by a frame of four compartments was used. Wheat flour, a representative of low-moisture foods, was packed inside the rectangular compartment to provide a density of 800 kg/m3. Afterwards, in the surrounding compartments, air, deionized water and NaCl solution were used for independent radio frequency heating tests. Two different electrode gaps (135 and 145 mm) were employed. The temperature of the sample was measured continuously using fibre optic probes at four different internal locations. The difference between the maximum and the minimum temperatures for three different cases (a: air, b: deionized water and c: NaCl solution) were as follows for electrode gaps of 135 and 145 mm, respectively: (a) 27.3 and 26.1 °C, (b) 2.5 and 4.8 °C and (c) 3.7 and 1.8 °C. Uniformity index values were also calculated. The results showed that temperature variation within the sample was greatly reduced when the sample was surrounded by deionized water or NaCl solution. PRACTICAL APPLICATION The project findings will provide processors with a practical means to achieve more uniform radio frequency heating of low-moisture foods.