A computer-based optimization technique was developed for determining the apparent heat transfer coefficient (h) for retortable pouches heated by circulated hot water under overriding air pressure. The technique incorporated actual process data, a finite difference model and an optimization criteria to converge on h values. A water flow channel was constructed to fit inside a vertical retort which allowed direct water exposure on the pouch surface at a quantifiable velocity. Because the optimization technique was not dependent on analytical equations, it could be applied to such areas as future heat transfer studies of new retortable pouch materials, designing new pouch-holding cassettes and improving water flow patterns in retorts.
Apparent heat transfer coefficients (h) were determined for the comeup, heating, and cooling cycles of thermal processing for retortable pouches heated by circulating hot water under overriding air pressure. Values for h were converged on by a computer-based optimization method that incorporated process data, a finite difference model, and optimization criteria. For retortable pouches thermally processed in circulating water under overriding air pressure, h values for the comeup, heating, and cooling cycles were found not significantly different (95% confidence). This indicates that in mathematical models a constant h value may be assumed for the three thermal processing stages. Also, there was no significant difference bctwccn h values for aluminum foil/plastic laminate pouches and all-plastic pouches during the combined come-up and heating stages. Thus, the same h value for a given process is applicable to either pouch type.
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