Doctoral Degrees (Mechanical and Mechatronic Engineering)

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Browsing Doctoral Degrees (Mechanical and Mechatronic Engineering) by browse.metadata.advisor "Coetzee, Corne"

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    Numerical and experimental performance evaluation of ventilated packages
    (Stellenbosch : Stellenbosch University, 2019-04) Fadiji, Tobi Samuel; Coetzee, Corne; Opara, Umezuruike Linus; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering (CRSES)
    ENGLISH ABSTRACT: Packaging serves a crucial role in reducing postharvest losses, particularly in the handling of fresh horticultural produce, and would be difficult to do without. Packaging protects the produce against mechanical hazards such as compression, impact, drop or vibration during distribution, ensuring its safe delivery to the consumers in a sound condition, at a minimum cost. Ventilated corrugated paperboard (VCP) packaging is being used extensively for handling fresh produce due to its capability to promote uniform and rapid cooling. However, the presence of ventilation openings jeopardises the strength of the package which could result in produce damage. As it is of utmost importance to ensure that the produce reaches its final destination without damage, continuous improvement in the package strength is paramount. Hence, this project aimed to gain a better understanding of the structural performance of VCP packaging to enhance the development of better and improved package designs. Firstly, a validated finite element analysis (FEA) model was developed to study the structural performance of an existing VCP package. This model incorporated some geometrical nonlinearities of the package. Paper and paperboard characterisations were done to determine the tensile properties, edge compression resistance and flat crush resistance. The tensile properties were used as input parameters in the model. The model was able to predict the compression strength of the package, and showed good agreement with experimental results, within 10%. Package liner thickness had a linear relationship with the compression strength. The stress in the package was found to be concentrated and a maximum at the corners. Subsequently, the FEA model was used to assess the strength of different package designs with emphasis on the influence of different geometrical configuration. The model was validated with experimental results. Increasing the vent area of the package reduced its compression strength. Packages manufactured with double-walled corrugated board performed better than single-walled board irrespective of the design, with the difference in strength as high as 72%. This study showed the importance of knowing the paperboard properties in the design of a package to improve its strength. Furthermore, the creep behaviour of different package designs was evaluated, and results showed load and environment conditions as significant factors affecting the creep rate. Increasing the applied load and relative humidity (RH) as well as reducing the temperature, accelerated the creep rate of the package. Also, package configuration also had a significant effect on the creep rate. Finally, to understand the deformation phenomenon of packages subjected to compression load, the displacement field of different designs was studied using digital image correlation (DIC), a full-field non-contact optical measurement technique. Findings showed that the distribution of the package displacement is largely heterogeneous. The displacement field in the out-of-plane direction was the largest while that in the horizontal direction was the smallest. Buckling was found to be a predominant phenomenon occurring at the centre of the package panels. Overall, this study provided empirical and numerical evidence for the design of improved packages, balancing the need for adequate structural performance and optimum cooling functionalities of the package.
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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.