Transfert de chaleur et de masse au cours du refroidissement des denrées périssables à bord des navires-durée minimale de refroidissement des cargaisons de fruits et légumes (dans les cales ou à l'intérieur des conteneurs)

Perishable goods (mainly fruit) are usually loaded aboard ships without precooling¹. The first phase of transport is therefore to cool the cargo down to the contractual carrying temperature as rapidly as possible. A priori, this implies that the ship's equipment can do this and in particular that the air distributing arrangement has been fitted for this purpose. The paper mainly deals with homogeneous cargoes having an even air permeability.In this Paper, the author adopts the conditions (extremely favourable) where the goods are directly exposed to the cooling fluid (with or without any protection against their drying out). These are conditions resulting in the minimum cooling time. The same calculation is applicable to any homogeneous cargo provided that the air distribution is properly balanced including that inside the packages (cases, boxes, etc). It may be locally applicable as well with the same conditions taking into account an unbalanced cooling air distribution system.The problems of cooling goods in large packages which the cooling air moves around is not dealt with: it leads moreover to prohibitive cooling durations and this case is to be avoided. This case is roughly approximated by a similar problem: the cooling of bodies with comparable sizes and shapes (plates, cylinders, spheres) with equivalent apparent conductivity which are suddenly put in a cold air flow maintained at an even and steady temperature. With such optimistic assumptions (where the heating is assumed to be negligible), the core and surface temperatures can be determined from the set of curves by Jacob⁹.The minimum cooling duration contemplated is the time needed to achieve a temperature in the whole cargo not too far from the carrying temperature. That temperature may exceed the latter by 2 or 3°C. In order to obtain it, all the basic cargo features are taken into account: breathing and, if necessary, desiccation as well as the rate of air circulation in horizontal and vertical ventilation.The functioning capabilities of the ship's equipment are also considered, on the one hand when starting and during the cooling down, if the available refrigerating capacity does not allow a step function as an initial condition, and, on the other hand, when the cooling air distributing system brings about a well known unbalance in the overall air flow distribution.