M. Ayub Hossain
Senior Scientific Officer (FMPE)
Bangladesh Agricultural Research Institute, Gazipur-1701
M. S. Hassan
Chief Scientific Officer (FMPE)
Bangladesh Agricultural Research Institute, Gazipur-1701
M. S. Islam
Director (Research)
Bangladesh Agricultural Research Institute, Gazipur-1701
M. Altab Hossain
Chief Scientific Officer (Agronomy)
Bangladesh Agricultural Research Institute, Gazipur-1701
M. Sq. Rahman
Professor
Dept. of AIE, HSTU, Dinajpur, Bangladesh
Germination, Solar collector, Solar radiation, Viability, Vigour
Bangladesh Agricultural Research Institute (BARI), Gazipur
Farm Mechanization
Design of the hybrid seed dryer was done based on the energy balance and heat and mass balance equations. The dryer consisted of a concentrating type flat plate collector, reflectors, auxiliary heating unit and drying chamber. The special feature of the dryer was that it could be operated in a sunny day using solar radiation and in a rainy or cloudy day or at night using auxiliary electric heaters. The length, width and height of the hybrid dryer were 3.0 m, 2.0 m and 1.0 m respectively. The collector was mainly composed by transparent cover, absorber plate, reflector and blower. The transparent cover of the collector was 1 mm thick clear plastic sheet. About 200 mm below the plastic cover; 2 mm black painted corrugated iron sheet was used as an absorber plate. To increase the efficiency of the solar collector, flat type reflector made of glazing stainless steel sheet was added on top of the collector. This reflector had adjustable angles that can be changed according to the sun’s angle during the day to collect higher amount of sun rays falling down to the solar collector. The solar collector was insulated by 15 mm thick polystyrene. A 0.75 kW axial flow blower was connected in one side of the collector to draw the atmospheric air in the collector and to push out the heated air to the dryer with a desired air velocity. For auxiliary heating, three electric heaters each of 2 kW capacity were installed at the end of the collector. A temperature controller was set to maintain constant temperature in the dryer. The dryer was placed on four 140 mm diameter wheels to move and turn the solar collector horizontally and change its direction according to the change of the sun’s angle. The drying chamber was located directly under the collector and 200 mm below the absorber plate. It was divided into three parts with equal dimensions. In each of the part there were two trays for drying the crops. Each tray was made of metallic frame and plastic net with dimensions of 1040 mm × 780 mm. The drying air was heated up in the collector and passed to the drying chamber through a curved passage at the end of the drying unit and flew over and under all the drying trays and exhausted from the outlet. The dryer was tested at Farm Machinery and Postharvest Process Engineering Division, Bangladesh Agricultural Research Institute (BARI), Gazipur during the period of 2009- 2010 for its technical performance evaluation. Firstly, the dryer was tested without any load to observe the temperatures at different points of the collector and drying chamber. During the test, ambient temperature, ambient relative humidity, temperature at different points in the collector and drying chamber, airflow at the outlet of the drying chamber, inlet and outlet temperatures, airflow in the drying chamber, reflected and global solar radiation were recorded at one hour interval. Then the dryer was tested for drying of paddy, wheat, maize and groundnut seeds. Freshly harvested grains were either purchased or collected from BARI farm. Five full load experimental runs were conducted for paddy and one experiment was conducted for each of wheat, maize and groundnut. During the drying test ambient temperature, ambient relative humidity, solar radiation, temperature at different points in the collector and drying chamber, airflow at the outlet of the drying chamber, moisture content of seeds were recorded at one hour interval. Temperatures were measured at one hour interval by a digital temperature meter (Model: K102, accuracy ± 0.3%, Conrad Electronics, Germany). Relative humidity was measured using a digital hygrometer (Model: E200, accuracy ± 0.5%, Conrad Electronics, Germany). A digital solar meter (Model: 776E, accuracy ± 3%, Digital Engineering, USA) was used to measure the solar radiation during the day time. Velocity of drying air was measured with an anemometer (Model: TA430, accuracy ± 3%, Airflow Ltd., England). The moisture content of seeds was measured by a grain moisture meter (Model: 8688 Speedy, XIBA, China).
International Journal of Energy Machinery, Vol. 5, No.1, pp. 42-52(2012.08)
Journal