UBC Theses and Dissertations
Comparison of thermal process evaluation methods for conduction heating foods in cylindrical containers Smith, Trudi
Five formula methods and three numerical general methods for determining thermal process lethality were compared with a reference method to demonstrate their applicability to conduction heating foods in cylindrical containers. Hypothetical centerpoint temperature history curves for cans with height to diameter (H/D) ratios of 0.1 to 3.0 were generated for a range of processing conditions using computer simulation. A finite-difference model based on Teixeira et al. (1969b) was used as the basis of the simulation program. The delivered lethality to an organism characterized by Z=10C° was evaluated using each of the methods and compared to the lethality calculated using the reference method. For each of the test methods, simulation data were provided for one minute intervals, but for the reference method, data were provided for intervals of 0.05 min. Each of the selected formula methods was adapted to allow calculations to be done by computer without operator intervention. The most significant part of this adaptation was the development of a system that enabled the computer to select the linear portion of the heat penetration curve to facilitate calculation of the parameters f and j which are required by all of the formula methods. A method for handling large tables was also developed for use with some of the formula methods. For the general methods, the deviations from the reference method were greatest when the heating rate index (fh) and H/D were small and the unaccomplished temperature difference (g) was large. Whereas the the value of fh was the most significant factor affecting the accuracy of calculations done using the general method, it did not greatly affect the performance of the formula methods. The factors that most significantly influenced deviations between the formula methods and the reference method were H/D and g. The largest deviations in all cases occurred when g was large and H/D was close to unity. These errors were mostly on the "safe" side, but the energy use implications could be significant, especially for high retort temperature processes.
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