Investigating cooling performance and energy utilization of refrigerated shipping container packed with fresh Fruit using computational fluid dynamics modelling

[摘要] ENGLISH ABSTRACT: This dissertation addresses a number of topics that arise from the use of arefrigerated shipping containers (reefers) during transportation of fresh produce. Thework contributes to (i) development of a computational fluid dynamics (CFD) modelof a reefer packed with fresh produce, (ii) simultaneous estimation of produce qualityand energy consumption to maintain product value and minimize wastage in the coldchain system. The work presented herein is concerned primarily with three topics: theairflow distribution in reefers (empty and packed), cooling operation of apple fruit, andenergy use with respect to packaging designs and fan operation. Additionally, a chapteris presented that focuses on the impact of environmental conditions on the performanceof fruit packed reefer during transportation.First, a numerical and experimental investigation of airflow and temperaturedistribution inside two types of empty reefers (T-bar floor and flat floor) used for freshfruit handling was conducted to establish the fundamental characteristics of transportphenomena. Then, a CFD model of a fully loaded reefer was developed using porousmedium approach. Fruit stacked pallets were modelled as porous media, in whichvolume average transport equations were employed, to avoid complex geometriesinside packed pallet and minimize computational cost. Wind tunnel tests were used toobtain the pressure drop characteristics of palletized stack of apple fruit and the viscousand inertia coefficients in Darcy-Forchheimer equation. The detailed structure of theT-bar floor of the reefer and resistance-to-airflow of wooden pallets that werepreviously overlooked, were incorporated in the model. Airflow, pulp temperature and,energy consumption data obtained from a fully loaded, full-scale reefer were used tovalidate the model. The validated model was used to further investigate airflow distribution and fruit cooling performance of packaging designs used for handlingapples and vertical airflow resistance or addition of bottom vent-holes.Energy consumption of reefers packed with apple fruit during shipping wasexamined experimentally and numerically using the validated model. The energyconsumption of reefers packed with different apple packaging designs was evaluatedwith respect to seven-eighth cooling time, which confirmed the influence of ventilationarea on energy use and the trade-off between the energy savings that can be achievedby employing packaging designs with low and high fruit packing density. In addition,the effect of evaporator fan on energy consumption was studied by simulating fruitpacked reefers operating at low, medium, high and variable evaporator fan speeds. Thestudy demonstrated significance of optimal fan speed operation on energy use ofreefers packed with stacked load of fresh produce.Finally, the impact of climate on cooling performance and energy consumptionof reefer during shipping was studied. The study showed an increase in fruittemperature and energy consumption due to heat conduction through the walls whenthe reefer operate in high temperature region. Overall, the CFD model developedpredicted airflow, heat transfer and energy use with satisfactory accuracy. The modeland research approach can be applied to a wide range of horticultural products and coldchains with slight modification.

[发布机构] Stellenbosch University