Performance evaluation of a cabinet solar dryer for drying red pepper in Bangladesh

Abstract

A cabinet type solar dryer was designed and fabricated over a collector and dryer area of 4.00 m2 and 7.5 m2 respectively for the geographical condition of Bangladesh. Red pepper was used to test the performance of the dryer. The upper tray and lower tray pepper drying needed 36 and 41 h to reduce moisture from 73% (wet basis) to 10% (wet basis) respectively and found 9 kg dried pepper from 30 kg fresh red ripe pepper. In contrast, open sun drying needed 85 h to reduce moisture from 73% (wet basis) to 11% (wet basis) and produced 2.43 kg dried pepper from 8 kg red ripe pepper. The average global radiation was about 133 W/m2 while the flux incidence and flux absorbed on collector was about 128 W/m2 and 103 W/m2 respectively. The average collector and dryer efficiency was about 48% and 34% respectively. The average exergy efficiency was obtained 63%. The average rate of top, bottom and side collector loss was 37 W/m2, 20 W/m2 and 3 W/m2 respectively. The upper tray, lower tray and open sun pepper seed germination was 76%, 81% and 85% respectively (P≥0.01). The redness value of lower tray pepper (a*=27.1) was higher followed by upper tray (a*=24.7) and open sun pepper powder (a*=21.1), which means direct exposure of sunlight diminishes the quality of pepper colour. The redness value of fabricated solar drying was significantly (P≤0.01) higher than that of open sun drying.