DESIGN, CONSTRUCTION AND PERFORMANCE EVALUATION OF EVAPORATIVE COOLER FOR PRESERVATION OF VEGETABLES

Abstract

Hexagonal evaporative cooler was designed, constructed and tested using locally available materials. This was used in the preservation of freshly harvested leafy vegetables. The capacity of the cooler was 2.21 x 105 em", It comprised of 3 chambers: the upper, middle and lower chambers. The cooler was installed under a shed built from bamboo poles and palm fronds. The essence of the shed was to reduce the effect of sensible heat gain from solar radiation. Two tests including "No load Test" and "load Test" were carried out on the cooler. The "No load Test" was the test carried out on the cooler to evaluate the effectiveness of three major pad materials (jute, wood shavings and latex foam).While the "load Test" was carried out during preservation of vegetables. Jute pad material was used on the cooler during "load test". Four common vegetables were used to conduct this test. These vegetables were Okra (Hybiscus escu/entus), Water leaf (Ta/inium triangu/are), Fluted pumpkin (Telferia Occidenta/is) leaves, and Amaranthus (Amaranthus spp.). 100 gm each of the freshly harvest produce were kept in each chamber of the cooler, and in ambient condition (outside the cooler) as control experiment. Three calibrated hygrometers were placed in the upper and lower chambers of the cooler, and the third one was placed outside the cooler for recording the wet bulb and dry bulb temperatures at these locations. Also recorded were the weight of vegetables with time of storage. Headings were taken on hourly basis from 7.00 am to 6.00 pm daily for 6 days. The mean temperature drop, mean wet bulb depression and mean saturation efficiencies were calculated. The corresponding relative humidities were also got from the psychometric table. Graphs were plotted and deductions were made as follows: The mean maximum temperature drop of the cooler was 8.5°C. The mean minimum & maximum dry bulb temperatures (dbt) of the cooler were 18°C and 24°C. Jute pad was observed to have the highest mean saturation efficiency (92%) followed by wood shavings (89%) and latex foam (86%). The cooler was able to sustain the weight and freshness of vegetables for more than 4 days in storage.