| Summary: | Electromagnetic heating (EMH) processes are being increasingly used in
the industrial and domestic sectors, yet they receive relatively little
attention in the thermal engineering domain. Time-temperature
characteristics in EMH are qualitatively different from those in
conventional heating techniques due to the additional parameters (viz
dielectric properties of the material, size and shape of the product
and process frequency). From a unified theory perspective, a
multi-purpose model has been developed in order to obtain the heating
characteristics for an arbitrary processing situation. Theoretical
analyses of various EMH processes in materials of various regular
geometries and a range of physical properties have been undertaken.
Despite the wide spread usage of microwave energy in the food
engineering sector. few understand microwaves and their interactions
with foods. Much of the published research is largely focussed from the
view point of an electrical engineer and aimed at the oven designer.
However, trial-and-error methods are usually employed when developing
microwavable food products and when using microwave ovens. The
presented thesis is focussed from the view-point of the thermal
engineer and aimed primarily at food developers and end users.
The multi-purpose model was then modified specifically for simulating
the heating of food materials in a microwave oven. The validity of the
commonly made assumptions was investigated; in particular the variation
of dielectriC properties during the heating processes and their likely
influence on the model's predictions. Experimental data available in
the literature were compiled and analysed to form a set of equations
for predicting the dielectric properties of various food materials.
Also available correlations for thermal properties were evaluated for a
selected set of experimental data of different food materials. Analyses
were undertaken to demonstrate and evaluate the effects of various
parameters on the heating characteristics of different food materials
commonly heated/cooked in microwave ovens. A qualitative comparison of model predictions and experimental measurements is provided to validate
the physical basis of the model. Findings from the model lead to a
better understanding of the interactions between foods and microwaves. [...cont.]
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