Three- dimensional temperature distribution of the packaged foods with different shapes during microwave heating

Temperature distribution characteristics of samples ( gelatin- agar with a moisture content of 99%) were studied with different shapes, such as rectangular, six- side cylindrical and the cylindrical, during microwave heating by experiments and simulations. Based on Maxwell's equations and heat transfer equations, models of three- dimensional temperature distribution were established using finite element method ( FEM) . The isothermal surface of the exterior surface, the intersecting surface and the interior surface of packaged foods with different shapes were investigated, and the correlated temperature differences among three surfaces were observed.Samples with the same volume, but varied in shapes, had distinct differences in the distribution of temperature, because the penetrated microwave energy samples formed various complex focusing areas. Upon microwave heating for 60 s, 4, 7 and 1 hot spots appeared in the rectangular, the six- side cylindrical and the cylindrical sample respectively, and the relevant temperature difference between the maximum and the minimum were 23.87, 21.92 and 25.10℃.The temperature distribution was concerned with the dielectric characteristics of certain samples.As to the sample, penetration depths of the microwave at 2450 MHz ranged from 10 to 25 mm, when the correlated temperature varied from 10 to 45℃. Based on three- dimensional models, the temperature distribution inside and outside of the packaged foods with different shapes could be described distinctly.