Solar drying of Andrographis paniculata using a parabolicshaped solar tunnel dryer

Abstract

Solar drying experiments of Andrographis paniculata were conducted in Nakhon Pathom, Thailand. For this purpose, a new type parabolic-shaped solar tunnel dryer was designed and manufactured. Solar dryer consisted of a flat-plate solar collector and a drying tunnel. The collector and the drying tunnel were covered with polycarbonate plates to reduce heat losses and placed in series. Heated air in solar air collector was forced through Andrographis paniculata by DC-fans driven by 15W solar cell modules. The total area of the collector was 108 m2. During the drying period, drying air temperature, relative humidity, air flow rates, solar radiation, and lose of mass were measured at different parts of the dryer for every 10minutes. To investigate its performance, the dryer was used to dry 100kg of Andrographis paniculata. The dryer could be used for Andrographis paniculata of 75% (wb) moisture content, and they could be dried within 2-3 days, with 7% (wb) remaining moister. The products being dried in the dryer got the heat from both the sunlight and the collectors. They were completely protected from rain, animals, insects and the dried products are of high quality. However, the temperature of the drying air was varied between 35 - 75 oC, depends on the weather conditions.