Optimizing air flow distribution in maritime refrigerated containers

Ever more intercontinental fruit transport takes place in reefer containers. The global installed fleet of 40 ft high cube reefer containers counts approximately 1,000,000 units. The reefer market has generally realized a compound annual growth (CAGR) of 5%. Product temperature requirements are very tight for highly temperature-sensitive fruit like grape and kiwi. Another application where temperature requirements are particularly tight is in cold treatment shipments, required as a quarantine measure by authorities of importing countries. In cold treatment shipments it is often hard to maintain the warmest product temperature below the regulatory imposed treatment limit, without causing chilling injury in the cold spots. Temperature gradients are reduced by good air flow distribution. T-bars make up the air ducts of reefer containers. Unfortunately most air escapes from the ducts before reaching the container door-end if no further measures are taken. An appropriate T-floor cover could help to guide more air to the locations where it is needed most. This paper reports on an experimental study with the aim to design an optimised T-floor cover and assess its effect on fruit temperature distribution. In a series of climate chamber tests it is investigated how temperature gradients are affected by four different T-bar cover designs. During the tests the container is stuffed with palletized empty cartons, with zero autonomous heat production. The results show clear positive effects of T-bar covers. The best of the four covers is non-perforated, of a trapezoidal-like shape, installed in the container with the narrowest end towards the door-end. It reduces the temperature difference between warmest and coldest measurement location by nearly 50%, and also accelerates temperature recovery after a power off period. In view of the promising results it is recommended to follow-up with real transport tests.