Design and Development of Solar Assisted Tray Drying System for Khoa Powder Preparation

A solar parabolic trough concentrator (PTC) air heater was designed, fabricated and coupled with an electrically operated tray dryer for drying Khoa, which was then converted to Khoa powder. The designed solar PTC air heater had collector aperture width of 1.016 m, collector length of 1.970 m, focal length of 0.226 m and rim angle of 96.6° with collector aperture area of 2.0 m². Two receivers made up of galvanized iron and aluminum coated with black paint on the surface were tested. Parameters like direct normal irradiance (DNI) and temperatures were recorded along with atmospheric air, receiver output air and receiver surface temperature from 9:00 h to 16:00 h. The average maximum outlet air temperature, receiver surface temperature and thermal efficiency were observed to be 62.8°C, 159.4°C and 21.71%, respectively for the galvanized iron receiver and 67.8°C, 170.4°C and 23.69% for aluminum receiver coated with black paint, respectively. The Khoa was made from full cream milk and dried in an electrical tray dryer coupled with solar PTC air heater at 55°C, 60°C and 65°C. The average thermal efficiency of the tray dryer at 55°C, 60°C and 65°C was 20.44%, 23.33% and 27.46 %, respectively. The average requirement of energy per kg moisture evaporation at 55°C, 60°C and 65°C was obtained at 3.25, 2.84 and 2.41 kWh, respectively. A comparative investigation on energy consumption for Khoa drying in a tray dryer without a PTC solar heater (2.65 kWh) was about 2.5 times compared to electrically heated tray dryer coupled with PTC solar heater (1.04 kWh).