Performance evaluation of the hybrid biomass supported heater solar dryer at Kangulumira

Abstract

An evaluation of the performance of an 8m by 4m hybrid solar dryer incorporating a biomass heater is presented in this thesis. The thesis compares the collector and drying efficiency, drying rate depending on the drying time using the solar dryer only and solar dryer with biomass heater incorporated in the drying process. The dryer consisted of; the trays, drying chamber, fans/blowers, solar battery, control panel and biomass air heater and the collector. The drying chamber was made of a metal framework, Visqueen covering and a concrete foundation. The collector (Solar collector) in the drying chamber was made of black oxide, gravel and hardcore as admixtures in the concrete to give the structure the desired structural strength and to improve the heat properties of the drying chamber and prevent heat losses in order to heat the inflowing air in the lower levels of the dryer. Two different load tests were carried out during the performance evaluation of the dryer. In the first load test, 450 g of pineapple slices were used to evaluate the performance of the dryer and a maximum temperature of 53.8°C was found in the dryer at an ambient temperature of 31°C during the day as a result of a rise of 8.1°C above ambient and this gave average dryer and ambient temperatures of 32.4°C and 24.3°C respectively. In this test, the pineapples were dried from an initial moisture content of 79% to a final moisture content of 9% within 20 hours of sunshine (almost two days) and 9.2% within 18 hours of sunshine (almost two days) for solar drying only and with a biomass heater incorporated (only in the evening) respectively. The drying rate and drying efficiency were also evaluated to be 10.04 kg/h and 25.76% respectively for solar drying only; 10.3 kg/h and 21.23% respectively when the biomass heater was used (only in the evening). The collector efficiency was also evaluated to be 18.18% for solar drying only and 18.21% when the biomass heater was used (only in the evening). The second test was also carried out using 900 g of pineapple slices to evaluate the performance of the dryer and a maximum temperature of 54.2°C was found in the dryer at an ambient temperature of 31.2°C during the day as a result of a rise of 8.2°C above ambient and this gave average dryer and ambient temperatures of 32.7°C and 24.5°C respectively. In this test, the pineapples were dried from an initial moisture content of 79% to a final moisture content of 9.6% within 20 hours of sunshine (almost two days) and 9.6% within 16 hours of sunshine (almost two days) for solar drying only and with a biomass heater incorporated (in the evening and in the morning) respectively. The drying rate and drying efficiency were also evaluated to be 10.04 kg/h and 25.26% respectively for solar drying only; 10.85 kg/h and 21.8% respectively when the biomass heater was used (in the evening and in the morning). The collector efficiency was also evaluated to be 20.26% for solar drying only and 17.84% when the biomass heater was used (in the evening and in the morning).