Pergamon Int. Comm. HeatMass Transfer, Vol. 23, No. 2, pp. 177-186, 1996 Copyright © 1996 Elsevier Science Ltd Printed in the USA. All rights reserved 0735-1933/96 $12.00 + .00 PII S0735-1933(96)00004-8 ADAPTIVE FINITE ELEMENT ANALYSIS OF MICROWAVE DRIVEN CONVECTION Addana S. Franca and Kamyar Haghighi Department of Agricultural and Biological Engineering, Purdue University West Lafayette, IN, 47906-1146, USA - e-maih haghighi@ecn.purdue.edu (Communicated by J.P. Hartnett and W.J. Minkowycz) ABSTRACT This study describes an adaptive finite element methodology for heat transfer by convection applied to microwave heating of liquids. This is the first attempt to model such type of problems employing the concepts of error estimation and mesh adaptivity. The proposed methodology is generic and can be applied to steady- state, transient, linear and nonlinear problems involving heat transfer by conduction and convection. There was very good agreeement between simulation and experimental results. Introduction Microwave heating has been applied to processing of food products since the 1950's. The food industry is the largest consumer of microwave energy where it is used for cooking, thawing, tempering, freeze-drying, pasteurization and sterilization [1]. Microwave processing involves transient heating conditions similar to conventional thermal processes, except that heat is generated by molecular friction resulting from dipolar rotation in polar solvents and from the conductive migration of dissolved ions, thus providing a volumetrically distributed heat source. The problem of natural convection in a fluid with heat sources has been extensively investigated. Both uniform [2,3,4] and spatially distributed [5,6,7] heat sources have been studied. Natural convection in a cylindrical container exposed to microwaves was studied by Datta et al. [5,6]. This study assumed an exponential decay for the absorbed microwave power, following a Lambert law behavior. Ayappa et al. [7] investigated the problem of natural convection of a liquid in a square cavity exposed to microwaves, using the finite element method. The authors concluded that, the greater the spatial variation of microwave power, the stronger the influence of the direction of microwaves on the uniformity of heating. They also concluded that convection plays the largest role in lowering the temperature span in the sample. 177