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/m2 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 R2 value of 0.9977 at 32°C. The activation energy was 104.05 kJ/mol.