Solar-powered evaporative cooler for fruits and vegetables in developing countries

Abstract

An investigation was undertaken into the potential of evaporative cooling using forced convection for the short-term storage of fruits and vegetables on a scale which was manually transportable by a single person and used a self-contained photovoltaic system. Previous research and existing products have primarily focused on the use of evaporative cooling with natural convection and there has been minimal evaluation of the possible improvements in performance realised with forced convection. Furthermore, food insecurity in developing countries is extensive with many cases of severe undernourishment due to the spoilage of the available food, where an affordable solution under =C45 to control wastage through preservation could be transformative in promoting healthier societies. With the aim of achieving a cooling effect with a temperature decrease of at least 11oC and relative humidity increase of at least 35%, a prototype of 6.62kg and 585mm by 405mm by 360mm was designed through analytical calculations and numerical simulations using a radial fan for optimal operation at ambient temperatures above 32oC and ambient relative humidities below 50%. Under practical experimentation in Johannesburg, South Africa, with a solar panel of 6.0W, the prototype was able to achieve the desired performance in 81.9% of the relevant periods using cotton ring spun and polyester for the cooling pad. This was complemented with an increase in shelf life by 88.3% on average for a sample of fruits and vegetables stored within the internal volume of 45L compared to an identical sample stored externally. For further optimisation, a thermoelectric module was incorporated with an additional solar panel of 7.0W. This enhancement resulted in an improved performance minimising the temperature fluctuations to 1oC for each 3.5oC fluctuation in ambient temperature on average, compared to the previous results of 1oC for each 2.4oC fluctuation in ambient temperature on average, at the expense of an unsatisfactory increase in costs of 83.8%. Overall, the performance was successfully promising and it is recommended for further practical experimentation under more extreme environmental conditions.