Doctoral Degrees (Mechanical and Mechatronic Engineering)

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Browsing Doctoral Degrees (Mechanical and Mechatronic Engineering) by Author "Berry, Tarl Michael"

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    Optimisation of multi-scale ventilated package design for next-generation cold chain strategies of horticulture produce
    (Stellenbosch : Stellenbosch University, 2017-03) Berry, Tarl Michael; Coetzee, Corne; Opara, Umezuruike Linus; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Corrugated fibreboard boxes (cartons) are used extensively in the cold chain to transport fresh produce from growers to consumers. These ventilated packaging systems have multi-scale structures and should facilitate suitable cooling of produce to preserve quality, protect against mechanical damage and enable efficient handling and transport. However, current designs often do not incorporate these factors and improved designs have been identified as part of new strategies to reduce postharvest losses and enhance overall cold chain efficiency. The aim of this thesis was to develop improved fresh produce packaging designs through the use of a novel multi-parameter evaluation approach, within the scope of a multi-scaled packaging system. To this end, computational fluid dynamics (CFD) models and experimental box compression tests were used to evaluate new packaging designs, to quantify spatio-temporal moisture distributions in cartons during shipping and to increase packing densities in refrigerated freight containers (RFC). Three new vent hole configurations were proposed and compared against an existing carton used for handling pome fruit. Results showed that the presence of trays reduced cooling efficiency by 31% in the standard commercial design. Conversely, the use of the newly proposed vent designs considerably improved both cooling efficiency and cooling uniformity by 48% and 79%, respectively. Next, the effect of vent hole area and board material was investigated. Results demonstrated that significant improvements in both cooling efficiency and carton strength are possible, using alternative vent hole designs. Additionally, a significant interaction, with respect to mechanical strength, was observed between board material properties (board type) and the vent hole design. This finding indicates that high humidity conditions (i.e. refrigerated transport) can substantially influence the expected mode of failure in cartons (mechanical performance). Furthermore, a CFD model was developed to predict spatio-temporal moisture distribution in cartons loaded in a RFC. The study of a standard shipping scenario showed that moisture gradients were relatively small, indicating that mechano-sorptive creep is likely not a major factor in this case. However, larger gradients are expected during less desirable conditions. These findings can be used as baseline conditioning treatments for future carton compression protocols. Lastly, two unique packaging system strategies were proposed and evaluated for cooling efficiency. Although both showed generally improved performance, the “Tes” design increased packing density by 12% and forced-air cooling efficiency by 29%, compared to standard designs. Findings also showed improvements in vent hole design for vertical flow (RFC) are still possible. Overall, research reported in this thesis contributes towards the development of a more optimal ventilated packaging design for use in the fresh produce cold chain. Significant advancements were also made with respect to the implementation of a multi-parameter evaluation approach, which should be further extended to future assessments of fresh produce supply chains both in academia and in commercial practice. Finally, significant knowledge gaps were revealed with respect to the mechanical performance of cartons under high humidity conditions. Future studies should therefore concentrate on the development of new predictive approaches to better assess the integrated performance of cartons under cold chain conditions.