Drying kinetics of natural rubber sheets under two solar thermal drying systems

Abstract

This work describes the thermal behavior and evaluation of kinetics drying of natural rubber sheets using two solar drying technologies: direct and indirect. The solar drying tests were carried out simultaneously in order to compare the behavior under same weather conditions. The moisture content of the rubber sheets was reduced from 45.8 to 0.59% and from 49.7 to 0.33% on a dry basis (d.b.) for direct solar drying and indirect solar drying, respectively. The direct drying mode was carried out for 12 days with average temperature and relative humidity inside the greenhouse, during sunny hours, of 37.04 °C and 14.1%, respectively. Meanwhile, the indirect drying operation was carried out in 9 days (61.62 h intermittently) with 61 °C and 4.77%, respectively. The average global energy efficiency of the field of SAH was 33.77%. Thirteen thin layer models were used to evaluate the drying behavior of which the Modified Henderson and Pabis model was the best to describe the solar drying of rubber sheets for the direct and indirect system. As a conclusion, the direct greenhouse-type solar dryer is recommended for small producers and the indirect tunnel-type solar dryer for companies with high and continuous production.