SOLAR DRYER WITH BIOMASS BACKUP HEATER FOR DRYING FRUITS: DEVELOPMENT AND PERFORMANCE ANALYSIS
Most solar dryers rely on only solar energy as the heat source. This condition limits its use in off -sunny periods such as cloudy, rainy seasons and after sunset. The objectives of this study were to: develop a solar dryer with biomass backup heater for drying fruits; analyze its performance; and carry out comparative analysis of the dryer with and without biomass backup heater. An indirect solar dryer was designed, constructed and analysed using 4mm slices of pineapples and mangoes. Temperature, humidity and ambient air temperature were measured using Tinytag data loggers, EasyLog – USB 2 and HI 91610C Thermo-hygrometer. A 300g weight of charcoal, costing GHC 0.5 (US$ 0.16)was fed into the backup heater every 1-2 hours with a running cost of US$ 1-2.88/day. The results showed that the moisture content (MC) of the pineapples reduced from 87% to 16%(wb) and that of mangoes reduced from 85% to 15.5% (wb). On average, solar
drying with backup took 14-18 sunshine hours to attain the desired MC, while that without backup took 20-27 sunshine hours. With biomass backup heater the drying rates were: pineapples (32.5g/h) and mangoes (19.3g/h), while without backup the drying rates were: pineapples (23.7g/h) and mangoes (15.5g/h). Better performance was obtained when the dryer was with a biomass backup heater.
Keywords: Moisture; dryer; temperature; solar; biomass