DEVELOPMENT AND PERFOMANCE EVALUATION OF A SOLAR-POWERED OVEN WITH PHASE CHANGE MATERIAL AS THERMAL STORAGE TO DRY VEGETABLES

Abstract

In a bid to forestall the problems amounted with the use of other energy sources for drying vegetables, this research work focused on the development of solar oven utilizing a phase change material (PCM) as heat storage system. Solar oven with the size of (457.20 x 457.20 x 457.20) mm3 was designed and constructed. It comprises of a two-layer drying tray and box-type phase change material, a molten salt, i.e. Sodium Nitrate and Potassium Nitrate (NaNO3 – KNO3) was selected as PCM and used for the research, with weight ratio 60 %:40 %. The 60 % NaNO3 – 40 % KNO3 has a phase change temperature of about 220 oC and stable thermal properties of 660 oC. Performance evaluation was carried out. Thus, dark green coloured okra was selected for the study. The okra was thoroughly washed and sliced using a sharp knife. The slices were weighed exactly 110 g for both oven-dry and the traditional sun-drying method. For sun drying, the weighed okra slices were taken in drying pan and kept on the open floor on the top of terrace. For solar drying, the weighed okra slices were taken in drying pan and kept inside the solar drying chamber. Observations on physiological loss in weight in each sample were recorded at the particular interval of 1 hour in both drying methods. The change in colour of slices was observed for further analysis. The maximum oven temperature during the study was recorded to be 68 ⁰C and the ambient temperature was 46 ⁰C. The fabricated oven was tested during the dry season for 9 hours each for three days and the efficiency of 52 % was obtained. The oven was lagged with glass fibre as insulator to prevent heat losses to the environment.