Performance Studies of Low Temperature Solar Drying of Fresh Tea Leaves ( Camellia assamica )

Low temperature drying or withering is the first step in tea processing after the tea leaves are harvested. The process of tea withering was conducted in a newly developed laboratory scaled withering trough coupled with a corrugated solar air heater during the months October and November 2019. The maximum withering air temperature was 32°C. The average relative humidity of the withering air was 80%. After 7 h of withering at an air temperature 27°C, the tea leaves attained around 60% moisture content. The average thermal efficiencies of the corrugated solar air heater for October and November 2019 were 63.15 and 56.06% at average solar radiations of 891 and 772 W/m 2 respectively. The overall efficiency of the withering trough was estimated as 40.98% with a specific energy consumption of 1.76 kWh/kg. Among the seven drying models used for fitting the withering characteristics, the Two-term model gave the best fit with R 2 value of 0.9977 at 32°C. The activation energy was 104.05 kJ/mol.