Temperature Distribution of Microwave Heating―Spheres and Cylinders

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Abstract
When irregularly shaped foods are heated with microwaves nonuniform temperature distributions with hot and cold spots are sometimes formed. These nonuniformities which can be ascribed to scattering and concentration effects have been studied in experiments using infrared thermography technique and in computer simulations of the temperature distribution in spheres and cylinders. Comparisons have been made between experimental and calculated results. The computer programs also have been used for studies of the influence of a number of variables: diameter, food composition and frequency. The experiments at 2450 MHz show that a heating concentration in the central parts occurs for spheres in a diameter range of 20 to 60 mm and for cylinders in the range of 18 to 35 mm. Comparisons between calculations and experiments show good quantitative agreement for diameters between 20 and 50 mm. As expected, a more pronounced core heating effect was noted for spheres than for cylinders. The calculations predict that at 915 MHz core heating occurs at diameters above 50 mm. The practical consequences of concentration effects are discussed, including the well-known explosion of eggs during microwave heating.

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