Microwave-assisted heating prototype designed for an interactive ready-to-heat foodstuff delivery system

Microwave (MW) heating is a rapid, efficient and low-cost technology widely spread for food industry processing and domestic use. The main limitation is due to the uneven heating and temperature management as the electromagnetic field interferes with conventional temperature probes. In this study was found a model to estimate the temperature of a MW-assisted heating prototype designed and exploitable for an interactive foodstuff delivery system made up of a vehicle loaded with a commercial MW oven controlled by a Raspberry PI 3 board, equipped with a touchpad screen and connected to a local network provided by a WiFi router. A contactless sensor (infrared probe), calibrated with a T type thermocouple, was used to detect the surface temperature of the item. The energetic efficiency of the prototype was estimated, based on the IEC 60705 standard, and four refrigerated products from Italian cuisine tradition were tested in the experiment. Their specific heat capacity Cp and the energy requirement Q to bring the temperature up to +75°C were calculated. The dish cooling time was also measured, which led to the determination of the convective heat transfer coefficient H to be used to determine the thermal power demand for the maintenance of the fixed final temperature. Based on the knowledge of energetic efficiency, Cp, Q and H, a suitable mathematical model has been developed for the MW power to be supplied during the heating process based on a simple balance equation of the thermal powers involved during delivery. A high correlation (R2=0.988) among the estimated and measured temperature was found, the energetic efficiency of the prototype resulted within 15 and 35%, depending on the foodstuff physical-chemical characteristics.