Modelling the forced-air cooling mechanisms and performance of polylined horticultural produce

Abstract

A 3-D computational fluid dynamics (CFD) model was developed to describe and predict the temperature profiles of palletised polylined kiwifruit packages undergoing forced-air cooling. The geometrical configuration of the kiwifruit, polyliner and cardboard box were explicitly modelled. The model included the effects of natural convection on the airflow behaviour and heat transfer process occurring within the packed fruits inside the polyliner. The capability of the model to predict the fruit temperatures in each package was quantitatively validated against experimental data. A laboratory scaled experimental rig was used to monitor the forced-air cooling process of a half pallet of kiwifruit boxes under controlled operating conditions. The numerical model was able to predict cooling times within experimental error.Cooling within the pallet was primarily influenced by air temperature and to a lesser extent airflow distribution into each package. A maximum recommended volumetric flowrate through the pallet of 0.34Lkg−1s−1, far lower than flowrates recommended for the cooling of non-polylined produce, was identified. Successive increases to the flowrate, particularly beyond 0.34Lkg−1s−1, resulted in increasingly diminished reductions (<12%) to cooling rate.Within the polyliner there was a low transfer of energy between kiwifruit and kiwifruit surrounding air. Instead cooling was reliant on the air temperature flowing over the top of the polyliner.