Looking inside a microwave oven for continuous flow heating by IR Thermography

A first attempt for on-line quantitative IR-thermography temperature readout has been performed inside an illuminated microwave oven. The main aim was to feature bulk temperature profiles in laminar pipe flow. The proposed procedure is intended to overcome the well-known difficulties connected with temperature retrieval while microwave (MW) heating occurs, while promoting high spatial resolutions. In fact, temperature measurements are usually taken onto few points by means of fiberoptic probes. Such an approach is often inadequate for properly controlling the process at hand, as strongly uneven spatial distribution of the temperature field is expected as a consequence of the electromagnetic distribution inside the cavity. Considering theoretical results already obtained by the authors, a linear distribution of the bulk temperature was realized for high water flow rates occurring in a circular pipe exposed to MW heating. Such an occurrence allowed a proper preliminary calibration based on which, a procedure for processing infrared images in real time is proposed. Experimental results related to two temperature levels, namely 40 and 50 °C, and two flow rates, that is 4 and 5.7 g/s, are reported. Experimental values of bulk temperature were compared with numerical results obtained by applying a 3D FEM model, developed by the authors, accounting for constant dielectric and thermal properties. A quite satisfying agreement between experimental and numerical data was found, retrieving better results with increasing flow rates.