Computer simulation, validation and optimization of quality retention of conduction heating foods in odd shaped containers.

摘要

Heat transfer models are effective tools for the analysis of thermal processing but their application is generally limited to simple geometries such as cylinders, rectangles and spheres. A conical and a finite elliptical cylinder are alternative shapes for products to be thermally processed. The objectives of this work were to develop heat transfer models to predict temperature distribution for conduction heated foods in any given size and shape of conically and elliptically shaped containers, to experimentally validate the models, and to use the models to predict quality or nutrient retention under different processing conditions with the goal of process optimization.; A finite difference method with energy balance approach was used for developing the models. The conically or elliptically shaped containers was divided into small volume elements. Energy balance equations were developed for each volume element and solved explicitly.; An acrylic material of known thermal properties was used to manufacture different geometries and sizes of 3 cones and 2 finite elliptical cylinder. Each geometry had 3 or 4 thermocouples (36 gauge, T type) inserted at different locations. Heat penetration tests were carried out in a water bath with constant or variable water temperatures. Experimental temperatures agreed well with temperatures predicted by the models.; The validated models were used to calculate lethality and quality retention under different processing conditions. All calculations were performed for a target lethality (F_o) of three minutes at the cold point. For a conically shaped container, the location of the cold point was searched. The effects of container geometry, food thermal diffusivity (from 1.2 to 1.6 m2/s), and surface heat transfer coefficient on the retention of quality parameters were investigated. The kinetic parameters of quality attributes were the D₁₂₁°_C value (from 40 to 240 min) and the Z value (from 10 to 60°C) which covered the range found in the literature. The range of the retort temperature was from 110 to 140°C The foods of high thermal diffusivity and/or foods packed in a container leading to a rapid heat transfer to the cold point required short processing times and retained more quality. Within the scope of this study, the optimum temperature for maximizing quality retention was highly dependent on the Z value of the quality factor while the D value, thermal diffusivity of food, surface heat transfer coefficient and container geometry had minor influence on the optimum processing temperatures.