Development and Performance Evaluation of Forced Convection Mobile Solar Tunnel Dryer for Drying of Silkworm Pupae

Abstract

Silkworm pupae are major by-products of silk reeling industry obtained after reeling considered as waste material and discarded in open environment. Dead pupae are highly perishable and found to be a rich source of protein and fat. Value addition to silkworm pupae can be enhanced by suitable preservation methods and by conversion of silkworm pupae into convenient processed products for wider market acceptability in different regions. In this study a forced convection solar tunnel dryer of 60 kg batch capacity was developed for drying of fresh silkworm pupae having size of 6.58 × 1.8 × 1.1 m (L × W × H) with MS square tube frame structure covered with 5 mm thickness toughened glass. The solar tunnel dryer consists of a solar collector section (6.48 m²) and drying section (4.32 m²) and a ceiling height of 1.1 m. In drying section four trays of size 1.2 × 0.9 × 0.08 m with mesh bottom were used to facilitate the loading and unloading of the silkworm pupae during drying. To reduce the heat loss from the dryer, closed thermopore were used as insulation material. The drying time required in open sun drying was 18–22 h and in the solar tunnel dryer was 7.5–9.00 h for different treatments of silkworm pupae from initial moisture content of 103.32–145.45% (d.b) to attain safe moisture content of 9.97–8.72% (d.b). To achieve higher drying rates, three axial DC fans, 20 W photovoltaic solar panel powered were fitted, to suck the moist air from drying chamber and push it out through a circular duct. The results showed that the drying rate of silkworm pupae under the solar tunnel dryer was found to be very high during the initial phase of drying due to higher moisture diffusion. The maximum temperature attained in the solar tunnel dryer was 95.6 °C at ambient temperature of 36.20 °C during drying period of silkworm pupae.