Exploring ambient loading of citrus fruit into reefer containers for cooling during marine transport using computational fluid dynamics

• Ambient loading of fruit directly into containers is a promising strategy.
• Vertical container cooling is explored as an alternative to horizontal precooling.
• Despite lower cooling rate and uniformity, 7/8ths cooling time <3 days was obtained.
• The impact of gaps between pallets on the fruit cooling rate was significant.
• Future developments should target faster and more uniform cooling.

A promising cold-chain protocol is explored as an alternative to the commonly-used forced-air pre-cooling (FAC) of citrus fruit prior to shipping: ambient loading of fruit in reefer containers for cooling during long-haul marine transport. Despite the multiple logistical and economical savings it provides, the potential of “ambient loading” of fruit in reefer containers has been left largely unexplored. The present study targets this practice, but also cooling by vertical airflow in general. Computational fluid dynamics (CFD) is used to identify differences in cooling rate and uniformity between individual boxes at different heights on a pallet and between individual fruit within a single box. Simulations show that low airflow rates, typical for refrigerated containers, do not only induce slower fruit cooling, compared to FAC airflow rates, but also the cooling heterogeneity between different layers of boxes (in height) and between individual fruit in a single box is larger. In addition, the presence of gaps between pallets invokes airflow short-circuiting, leading to highly reduced fruit cooling rates. Finally, strategies for future improvement of the ambient loading protocol are proposed, which in the first place should target faster and more uniform cooling.