Rapid air cooling of fresh agricultural produce can be achieved only by forcing cold air through the bulk of produce in order to carry away the heat from each individual commodity. The cooling rate in a given system depends mainly on the velocity of cold air flowing through it. Usually, this is the only controllable factor, since no changes can be made in certain fixed factors such as size, shape and thermal properties of the produce. Also, temperature of the cold air cannot be reduc~d below a certain safe point.

In a system with constant parameters, the coefficient of heat transfer, h, is proportional to the air velocity, V, around each unit area of the produce. In some definite cases (particularly with regularly shaped and homogeneous materials), the system's parameters can be found, and the relationship between h and V can be established.

When cooling packed agricultural produce, which obviously does not have regular shapes and is not homogeneous, the relevant air velocity, V, and some other parameters related to size and shape of produce cannot be clearly expressed in a general formula. But empirical connection between approach air velocity, Va, (that is velocity of air approaching a cross section of the package), and cooling rates have been found for most agricultural commodities in various packages and stacking patterns.

In general, most fruits and vegetables are cooled after being packed. In order to enable air movement around each individual product, containers must have ventilation holes. These holes, which constitute a relativ.ely small percentage of the envelope area of a container, impose a resistance to the air flow in addition to the resistance of the packed produce. Amp~e data has been gathered on cooling rates in various configurations of commodities - packages - air velocity, 1,2 but little information is available on the individual as well as the combined influence of packed produce and containers with vent holes on air flow rates.