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Journal of Microwave Power
and Electromagnetic Energy (JMPEE) |
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TITLE |
Thawing of Foods in a Microwave
Oven I: Effect of Power
Levels and Power Cycling [PDF] |
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AUTHORS |
M. Chamchong and A. K. Datta 1999 34 1 8-21 |
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Abstract Microwave thawing is
faster than other methods, but it can produce significant non-uniformity of heating.
The objective of this study was to perform comprehensive experimentation and
heat transfer modeling to relate the time to thaw
and the non-uniformity of thawing to power cycling, power level and the
surface heat transfer coefficient. The governing energy equation was
formulated with an exponential decay of the microwave flux from the surface.
Surface microwave flux was obtained from the measured temperature rise using
inverse heat transfer analysis. Gradual phase change was formulated as an
apparent specific heat, and was obtained for the experimental material tylose from differential scanning calorimetry
(DSC) measurements. The temperatures were measured immediately following
heating with a fast response thermocouple. Dielectric properties were measured
above freezing. Results show that the microwave flux at the surface and its
decay are affected by the changes in the power level. Power cycling has an
almost identical effect as continuous power at the reduced level of the
average cycled power. As power level increases, the surface flux increases by
the same fraction. At higher power levels, however, the outside thaws
relatively faster. A "shield" develops due to a much reduced
microwave penetration depth at the surface. This thawing time at higher power
levels is reduced considerably. Temperature increases initially are
non-uniform since the surface is heated at a faster rate than the interior.
In keeping with the assumption that once the temperature reaches Key Words: Key Words: dielectric properties, heat transfer, gradual phase change, non-uniformity |
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