Characterization of a combination oven prototype: Effects of microwave exposure and enhanced convection to local temperature rise in a moist substrate

The combination of microwaves exposure with the classical convection heating is seen as a practical solution to improve the uniformity and control of pure microwave heating of moist porous substrates. In the present paper, the complex coupling of electromagnetic exposure and enhanced fluid flow and heat transfer is explored, with an emphasis on the competition of such different mechanisms. To this end, some simple experimental techniques have been adopted to determine the thermal response of a common biological substrate in a microwave/jet-impingement oven prototype (1. kW of nominal power), allowing for the local characterization of its electromagnetic and fluid dynamic behavior. A rational approach is proposed by presenting a number of descriptors to help identify the interrelationships for all phenomena at stake, including the total process time (up to 1. min), the jet temperature (in the 60-100 °C range) and Reynolds number (in the 8000-15. 000 range). Therefore the effects of microwave exposure and relaxation times, working air velocity and temperature on the substrate's local temperature rise, are reported and discussed. Even in the explored range of microwave and jet thermization potentials investigated herein, different substrate portions experienced different temperature rises. The proposed configuration and analysis can be used to exercise due control of material conditioning and treatment in a combined microwave/forced convection framework