Drying air temperature profile of independent hybrid solar dryer for agricultural products in respect to different energy supplies (a research note)

Abstract

Drying is an important process of food preservation for security and sovereignty. The lack of conventional source of energy and limited supply of electricity urge to develop dryers for agricultural products adaptive to renewable energy sources and electricity independent. The invented dryers should then be able to generate various drying temperatures to accommodate variety of agricultural products to be dried. This study aims to explore the drying air temperature generated by so-called the independent hybrid solar dryer in respect to different energy supplies. The dryer consists of a drying chamber of 4.6 m3 capacitieswith five stories of ten trays inside, a chimney equipped with turbine ventilator, a heat exchanger embedded to furnace, and double heat collectors. Whole structure of the dryer is covered by transparent glasses and occupies 13m2 horizontal area. The dryer operates in three modes i.e. solar energy, energy produced by fuel combustion, and simultaneously solar energy and fuel combusted energy. The dryer can operate any time and in any weather condition. So it is suitable to be installed in remote area to produce hygienic dried products. In this experiment, the dryer was tested without load (product to be dried), when operated with solar energy and energies produced from biomass and coal combustions. The experimental result revealed as follows. When operated with solar energy with average radiation intensity of 956.4 W/m2, the dryer generated drying air temperature of 47.1°C which was 12.8°C higher than that of ambient air. Operated with the heat energies from both the coffee by product and coal combustions, the relationship between temperatures and fuel supplies were T = 4.323 s + 22.57 (R2 = 994) and T = 5.003 s + 22.57 (R2 = 0.998) respectively, where T = drying air temperature (°C) and s = fuel supply (kg). This dryer would be able to be operated for wide varieties of agricultural products according to the required temperatures.