9887

Heat Balance in Freezing and Thawing Food

This Demonstration calculates the ideal net heat added or removed to thaw or freeze 1 kilogram of food. You can input the initial and final temperatures, freezing point, heat capacity above and below the freezing point, and latent heat. It is assumed that these thermal properties are constant over the pertinent temperature range. The result is given in kilojoules per kilogram. A schematic plot (not to scale) displays the freezing or thawing process, showing the initial, final, and freezing or thawing temperatures.

SNAPSHOTS

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DETAILS

Snapshot 1: freezing pure water
Snapshot 2: thawing a meat-like product
Snapshot 3: thawing pure water ice
The net heat, , in kJ kg-1, is calculated using the formula
, where is the food's heat capacity above freezing in , is the temperature drop or rise above the freezing point in °C, is the latent heat in , is the heat capacity below freezing in , and is the temperature rise or drop below the freezing point in °C. The initial, final, and freezing point values as well as the food's thermal properties are entered with the sliders. The schematic graphical display below the calculated value depicts the process on an arbitrary time scale in which the heating or cooling stages are shown as straight lines and the freezing or thawing stage as a horizontal line. Note that the temperature versus time relationships during heating or cooling are not actually linear. The Demonstration lets you enter combinations of thermal properties that might not be found in real foods.
Reference: R. L. Earle and M. D. Earle, Unit Operations in Food Processing, NZIFST, Inc., 1983.
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