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Mathematical modeling of heat transfer in the cooling of fruit in closed containers

Bazan, Tomas.

Thesis of Ph.D., University of Florida, United States, Florida. 1989, 142 pages.

1989

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MATHEMATICAL MODELING OF HEAT TRANSFER IN THE COOLING OF FRUIT IN CLOSED CONTAINERS.

Postharvest technology known as room cooling to retard physiological deterioration of perishable commodities has become increasingly difficult to carry out as the procedure of tight stacking on pallets with little or no ventilation has become more common in practice.  Yet, several operational and economical advantages make this method of cooling convenient for a variety of applications in this country as well as in less developed nations.

 There is considerable interest at the present time in developing an efficient mathematical model that contributes to the understanding of basic heat transport mechanisms relating to the process of room cooling of fruit.  It is envisioned that such a model could be effectively used in the prediction of the three-dimensional temperature response and room cooling times for fruit bins stacked in commercial packing arrangements.

 In this study, a mathematical model was developed which accurately predicts the three-dimensional temperature response during the room cooling of a confined bin of spherical fruit.  The model accounts for the contribution of heat conduction through fruit contact areas as well as convective buoyancy effects on the removal of field and internally generated heat from fruit.

 Experiments to validate the model were conducted with tomatoes arranged in pattern and random packs inside a closed, uninsulated container.  Very good agreement between experimental and simulation results was obtained for the various room air speeds and packing arrangements used in packing houses.

 The results depict a more significant contribution of heat removal across contact areas for fruit located in the core of the bin than near walls.  The influence of natural convection velocities was found to cause the displacement of the maximum temperature location from the center of the bin upwards as cooling advanced.  Packing arrangements with high numbers of contact points exhibited faster cooling rates.  Adequate ventilation and room air velocities cut cooling significantly.  Simulation of fruit containers stacked on top of each other yielded cooling times as much as 40% longer than those of containers with all walls exposed to room air.