Performance comparison of microwave cavities used for extraction operations

In the agri-food industry world, billions of tons of waste are produced every year. This represents both a direct loss (due to the failure to exploit their potential value, and their nutritional and energy content) and indirect loss, due to their necessary treatment and/or disposal. Some substances contained in the wastes, of potential high value, can be recovered by means of extraction. Conventional extraction processes involve the use of solvents, which end up requiring an additional process of separation from the solute identified as the desired product. In recent years, extraction techniques have been proposed without the use of solvents. This work compares the performance of two microwave cavities used for extraction operations, both working at 2.45 GHz.A calorimetric analysis performed by following the heating rate and temperature evolution in rack of 25 beakers filled with 25 mL of water, coupled with the solution of the heat transfer balance in the system, allowed to build the spatial distribution of the electromagnetic power dissipated as heat in each of the beakers. Fluid-dynamics aspects related to the recovery of the vapour phase produced during the extraction were also analyzed, with particular emphasis on the mean residence time of the vapour fraction in the extraction chamber as a function of its configuration.