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sur le développement des zones arides et semi-arides

Titre : Modelling of micro-environment inside evaporatively and coolbot cooled stores using computational fluid dynamics models and changes in quality of stored tomatoes.

Auteur : Tolesa, Getachew Neme.

Université de soutenance : University of KwaZulu-Natal

Grade : Doctor of Philosophy in Agricultural Engineering 2018

Résumé partiel
The postharvest loss of fresh produce is a global problem, with the tomato fruit being subjected to a 30-50% loss of total production after harvest. The cost and the technicality of modern technology, including mechanical refrigeration, are not appropriate and sustainable for small-scale and middle-income fruit and vegetable farmers. Low-cost cooling technologies, such as evaporative cooling (EC), CoolBot-air-conditioning (CBAC) and a combination of the two (EC+CBAC), provide alternative solutions to minimize postharvest losses. However, there is insufficient information on the modelling of airflow, heat and mass transfer, using the computational fluid dynamics (CFD). The aims of this study were : i) to investigate the real-time airflow pattern, temperature, enthalpy, heat flux and relative humidity distribution inside the unloaded evaporative cooler and CoolBot-air-conditioner cooling systems, using CFD modelling techniques, ii) to evaluate the effect of inlet air characteristics on the airflow resistance inside the selected appropriate semi- and fully-loaded cold storage chambers, iii) to screen the best combinations of pre-storage disinfection treatments, combined with the low-cost cooling technologies, in terms of changes in quality of tomato fruit, and iv) to develop predictive models for the estimation of changes in quality and probability of marketability, using experimental data, obtained during the storage of tomatoes, after they have been subjected to different postharvest treatments and low-cost cooling technologies. The specific aim of this study was to investigate the real-time airflow pattern, temperature and heat flux inside EC, CBAC and EC+CBAC storage systems, using CFD models, to evaluate the changes in the quality of stored tomatoes and to develop predictive models for quality changes of tomatoes stored under EC and CBAC. The experimental results showed that the indirect heat exchanger (IHE) and one evaporative cooling wet pad were sufficient to reduce the temperature of the hot ambient air from 34.1℃ to 22.82℃. However, using multi-layer evaporative cooling pads was proven to have significant importance in increasing the relative humidity of air leading to the storage chamber. The EC+CBAC combination was the best for maintaining an optimum temperature (8-15°C) and relative humidity (80-99%) of the micro-environment inside the cold storage chamber during the storage period. A computational fluid dynamics (CFD) model was used to investigate the airflow, temperature and heat flux across the IHE and psychrometric unit.

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