A B S T R A C TA 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 0.34 L kg À1 s À1 , far lower than flowrates recommended for the cooling of non-polylined produce, was identified. Successive increases to the flowrate, particularly beyond 0.34 L kg À1 s À1 , 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.

No abstract

Flowrate and distribution of air is a critical design factor in the cooling, refrigeration and drying of horticultural food products. These operations rely on a constant supply of air distributed throughout bulk arrangements of the produce. Local distribution of the air is critical to optimizing the design and efficiency of these processes. Identification of the key parameters affecting the airflow distribution has been done either experimentally (using intrusive point-wise or bulk measurement techniques) or numerically. The detailed information provided by the use of computational fluid dynamic models has facilitated unique opportunities to investigate alternative system designs, without the need for expensive and time consuming experiments. This study provides a review of the techniques available to measure airflow (thermal and rotatory vane anemometry, pressure differential devices, tracer gases, LDA and PIV). Their advantages and disadvantages (accuracy, resolution, application range, cost, and ease of use) as well as their application in the validation of numerical models are reviewed. The novel and scientifically based design guidelines developed by a better understanding of the airflow behaviour within the system for each of the operations under study are also presented.

No abstract