Pergamon Int. Comm. HeatMass Transfer, Wol. 27, No. 4, pp. 527-536, 2000 Copyright © 2000 Elsevier Science Ltd Printed in the USA. All rights reserved 0735-1933/00/S-see front matter PII S0735-1933(00)00135-4 FINITE ELEMENT ANALYSIS OF MICROWAVE HEATING OF SOLID PRODUCTS Marcos E. C. Oliveira and Adriana S. Franca Universidade Federal de Minas Gerais - Departamento de Engenharia Quimica R. Espirito Santo, 35 - 6 ° andar 30160-030 Belo Horizonte, MG - BRAZIL - e-mail: franca@deq.ufmg.br (Communicated by J.P, Hartnett and W.J. Minkowycz) ABSTRACT In this paper, the electric field distribution obtained from solving Maxwell's equations was coupled to the energy equation to predict the temperature distribution during microwave heating of solids. The effect of sample rotation was incorporated to the model. Simt, lation runs showed that rotation of the sample results in a more uniform temperature distribution. In small samples, heating was more pronounced at the center, whereas in large samples, beating was also significant near the surface. The results also showed that power absorption is more effective at lower frequencies. © 2000 Elsevier Science Ltd Introduction Microwaves have been used as a heat source since the 1940's [1]. Application areas include polymer and ceramics industries [2,3], medicine [4,5] and food processing [6,7,8]. The food industry is tile largest consumer of microwave energy where it is used for cooking, thawing, tempering, freeze- drying, pasteurization, and sterilization [2]. Microwave energy penetrates a food material and produces a volumetrically distributed heat source, due to molecular friction resulting from dipolar rotation of polar solvents and from the conductive migration of dissolved ions. The dipolar rotation is caused by variations of tile electrical and magnetic fields in the product [8]. Heat is generated throughout the material, leading to faster heating rates and shorter processing times compared to conventional heating, where heat is usually transferred from the surface to the interior. However, the application of microwaves can result in uneven heating of certain products, depending on their dielectric and thermophysical properties [7,9]. This problem is more significant when processing at low frequencies, where the dielectric properties are considerably dependent on temperature variations. 527