The use of microwaves is an effective way to obtain a quick thawing of frozen foods. However, a non wished phenomenon, called thermal runaway, appears during such treatments. A relevant solution to prevent from this drawback consists in coupling to the microwave power a cold tangential air blast and thus to consider the microwave power and the air velocity as manipulated variables. The heat transfer is modelled via the effective heat capacity method and a source term representing the electromagnetic/heat energy conversion inside the product. The control of the heat transfer is carried out with a LQ approach extended to non linear systems and based on a reduction of the heat equation using finite volumes. The internal temperatures, required by the controller, are estimated with the well-known Extended Kalman Filter. Results obtained in simulation are discussed and finally a simplified version of the control (constant air velocity) is tested experimentally during thawing of a block of tylose.
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