Heat transfer in a combination microwave-jet impingement oven

Combination heating of food using microwave and jet impingement has been simulated by coupling Maxwell's equations of electromagnetics with energy equation and using experimentally measured heat transfer coefficient values for jet impingement in a novel domestic oven. Transient food temperatures from the model and experiment for each separate heating mode and their combination revealed the characteristic nature of each of the heating modes. Contour plots of temperature show that with combination heating, surface can be heated faster (for crispness) and edge over-heating can be partially avoided. Measures of non-uniformity in temperatures in the heated food are developed using coefficient of variation and middle 80-percentile range as the parameters. Using these measures, it is shown that combination heating leads to more uniform heating, without compromising the speed or convenience. A 22-30% increase in uniformity has been observed for combination microwave-jet impingement heating over microwave-only heating. jet impingement is a good complement to microwave heating as it has different spatial and time variation of heating rates. During the initial period, jet impingement dominates over microwave heating near the Surface, with microwave heating being more significant in the interior. At later times, the roles switch with microwaves becoming more dominant on the surface while jet impingement takes a more significant role in heating the interior of the food. These findings should help the product, process and equipment designer achieve the balance between speed and uniformity of heating in a more precise manner. 0 2007 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.