29D-10 |
Total and transient energy consumption for thermal processing of canned foods |
R. J. SIMPSON, Procesos Quimicos, Biotecnologicos y Ambientales, Univ. Tecnica Federico Santa Maria, Avenida España 1680, Valparaíso, 5632, Chile, C. A. Cortés, Procesos Químicos, Biotecnológicos y Ambientales, Universidad Técnica Federico Santa María, Avenida España 1680, 5632, Chile, and S. F. Almonacid, Procesos Químicos, Biotecnológicos, y Ambientales, Universidad Técnica Federico Santa María, Avenida España 1680, Valparaíso, Chile. Thermal processing is an important method of food preservation in the manufacture of shelf stable canned foods, and has been the cornerstone of the food processing industry for more than a century. Although the literature in food science and thermal processing is very extensive, most of the references deal with the microbiological and biochemical aspects of the process. In batch retort operations, maximum energy demand occurs only during the first few minutes of the process cycle to accommodate the venting step, while very little is needed thereafter in maintaining the process temperature. The aim of this research was to develop a mathematical procedure to estimate total and transient energy consumption during the heat processing of canned foods. The transient energy balance for a system defined as the retort, cans without their contents, and the steam and condensate in the retort requires no work term. The heat transfer terms include radiation and convection to the plant environment, and heat transfer to the food in the can. Equations were solved simultaneously and heat transfer model was solved using an explicit finite difference method. Correlations valid in the range of interest (105°C through 140°C) were used to estimate the thermodynamics properties of steam and condensed water. Computer models were developed on the basis of unsteady state heat transfer to estimate total and transient energy consumption. Close agreement was observed between experimentally determined heat consumption and the ones (total and transient) obtained by utilizing the developed mathematical models. Analyzing individual terms, the most relevant were the heat lost through the vent, heat absorbed by food and heat lost through the bleeder. The development of a transient energy balance in a batch retort will allow an optimum scheduling of retort battery in the plant and also allows the identification of variable temperature profiles that can be used for optimum process conditions.
Session 29D, Food Engineering: Thermal processes
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