Experimental performance of a solar tunnel dryer for drying silkworm pupae

The objective of this study was to conduct an experimental analysis to investigate the performance of a mixed mode type forced convection solar tunnel dryer (STD) which was used to dry silkworm pupae under tropical weather conditions of Mahasarakham, Thailand. The dryer consisted of a transparent glass covered flat-plate collector and a drying tunnel connected in series to supply hot air directly into the drying tunnel using a blower. The dryer was 6.2 m long and 1.8 m wide. The drying unit had a loading capacity of 30 kg of silkworm pupae. The effect of the drying air flow rate was examined. The drying time depended on the drying air flow rate and temperature. Moisture content of the silkworm pupae was reduced from 3.70 kg H2O kg−1 dry matter to 0.20 kg H2O kg−1 dry matter in 570 min at the corresponding air flow rate of 0.30 kg s−1 and it took 945 min in open sun drying; drying time was reduced by about 40%. A quality assessment shows that the lipid content of the dried silkworm pupae was not affected by the STD. A slight decrease of polyunsaturated fatty acid (PUFA) was observed. Maximum drying and overall efficiencies were 30.14% and 19.68%, respectively, at the air flow rate of 0.30 kg s−1. The economic analysis indicates that the payback period is 1.42 years. Due to its simplicity, the proposed system is relatively inexpensive. Therefore, commercial application seems to be viable.