Experimental and Theoretical Study of Thompson Seedless Grapes Drying using Solar Evacuated Tube Collector with Force Convection Method

An evacuated tube solar collector drier is designed and developed to study analytically and experimentally drying kinetics of Thompson seedless grapes in Pune, India. Drying experiments are carried out in the month of April- June for continuous three years from 2013-2015. During the experimentation, temperatures of hot and cold air at various places, ambient relative humidity and humidity variation in drying chamber, wind velocity and mass of the grape are measured on hourly basis. 10 kg of Thompson seedless grapes are dried in forced convection heat transfer mode from initial moisture content of 76% (wb) to final moisture content of 15%(wb) in 37 hours. The drying is carried out under the uncontrolled conditions. The average evacuated tube solar collector efficiency is found to be 24.5% whereas the stacked type dryer which is insulated from outside has given drying efficiency up to 37.1%. To study drying behavior analytically nine different drying models have been tested. It is observed that, Page model describes the drying behavior accurately with highest coefficient of determination (R^2 = 0.993), lowest reduced chi-square (χ^2 = 5.19x10^-5) and lowest root mean square error (RMSE = 0.02071).