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Heat Penetration Rates of Natural Convection Heating Liquids in Metal Containers
1University of Minnesota, Department of Food Science and Nutrition, 1334 Eckles Ave., St. Paul, Minnesota 55108.
Journal of Food Protection
|May 25, 2019
Summary
Heat penetration (HP) testing reveals that liquids heating by convection form curves, not straight lines, on semilogarithmic graphs. The f-value increases with heating time for these fluids.
Area of Science:
- Food science and technology
- Chemical engineering
- Thermal processing
Background:
- Accurate heat penetration (HP) data is crucial for validating thermal processes in canned foods.
- Conventional HP analysis assumes linear heating curves, which may not apply to all heating media.
Purpose of the Study:
- To investigate the heat penetration characteristics of various liquids, including water and 16 different fluids.
- To determine if natural convection heating liquids deviate from the expected linear heating curves in semilogarithmic plots.
Main Methods:
- Collected HP test data for water in 13 can sizes and 16 fluids in 211 × 400 cans.
- Fitted straight lines using least squares regression to specific (T1 - T) ranges for f-value determination.
- Analyzed data until the slowest heating zone reached within 0.1 C° of the heating medium temperature.
Main Results:
- Natural convection heating liquids produced curved lines on conventional HP graphs, deviating from linearity.
- Determined f-values by fitting lines to data segments, revealing an increase with heating time.
- The study confirms that semilogarithmic plots of HP data for convective heating fluids are inherently curved.
Conclusions:
- The assumption of linear heat penetration is invalid for fluids exhibiting natural convection.
- The f-value of convective heating fluids increases over time, reflecting the dynamic heating process.
- Accurate thermal process design requires acknowledging the curved nature of HP data for such fluids.
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