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Development and Adoption of a Solar Cabinet Dryer for Vegetable Seeds (2019-2020)

M N Amin
Scientists
Farm Machinery and Postharvest Process Engineering (FMPE) Division, BARI, Gazipur

M A Hossain
Scientists
Farm Machinery and Postharvest Process Engineering (FMPE) Division, BARI, Gazipur

T N Barna
Farm Machinery and Postharvest Process Engineering (FMPE) Division, BARI, Gazipur

Abstract/ Executive Summary:

A solar cabinet dryer was designed and fabricated at Farm Machinery and Postharvest Process Engineering Division, Bangladesh Agricultural Research Institute, Joydebpur, Gazipur for drying of 10-20 kg of moist vegetable seeds. Dried seeds of red amaranth (7.95 kg) was used for testing the performance of the dryer during 30-31 January 2020. The moisture of red amaranth was reduced from an initial moisture content of 17.76% wb to the final moisture content of 7.0% (wb) in 8 hours. Dryer was tested using electric energy (5 kW electric heaters) without load. Temperature of drying chamber increased and relative humidity decreased during the drying period. Average temperature in the heater zone was 10.4 °C higher and relative humidity was 31.1% lower than those of ambient conditions. Solar energy was also used for testing of dryer without load. Drying air temperature of bottom tray was higher (1.21°C) than that of top trays but at successive upper trays temperature was gradually decreased. Temperature of all trays varied from 42.77°C to 43.98°C which is suitable for drying of vegetable seeds. Dryer was tested with freshly harvested seeds of sweet gourd (616 g) during 24-25 June 2020. Average temperature of heater zone, bottom tray and upper tray were found to be 43.99°C, 42.70°C and 41.57 °C and relative humidity of the said positions were 44.00%, 46.60% and 49.25% respectively. The moisture content of sweet guard seeds was reduced from 41.59% to 9.23% (wb) in 6 hours of drying period. Germination of dried sweet guard seeds was found to be 98%. One batch of training program of solar cabinet dryer among farmers and seed growers was conducted at RARS, Jashore on 8 February 2020. Farmers of Jashore showed interest to use the dryer. Heating unit of the dryer was rearranged for minimizing temperature differences among the trays. A prototype of solar dryer was fabricated for demonstration in the project site.

Keywords: Solar, Vegetable seed dryer, Technical performance, Economic performance, Vegetable seeds, Seed growers

Location: Chuadanga district, Bangladesh

Start Date: 00-00-2019

End Date: 00-00-2020

Program Area: Farm Mechanization

Commodity: Vegetables, Seeder, Drier

Objectives:

The main objectives of this present experimental work are, (i) Designing and fabrication of solar assisted vegetable seed dryer; (ii) Evaluation of technical and economic performance of dryer for producing quality vegetable seeds; (iii) To test and demonstrate the dryer in the farmers’ fields; (iv) To disseminate the dryer among the seed growers and traders through training, field demonstration, workshop and printing media.

Methodology:

Performance test of the dryer with amaranth seeds The dryer was tested for drying of red amaranth seeds. The moist seeds of red amaranth were collected from Chuadanga last year for testing of solar cabinet dryer. The seeds of 7.95 kg that was dried at 7% moisture content. Water was mixed with dried seeds for higher moisture content about 18 percent on the wet basis at FMPE Division, BARI, Gazipur during 30- 31 January 2020. Moist seeds were kept in normal refrigeration for 24 hours and later it was kept in ambient room temperature for 24 hours attaining equilibrium moisture content. Then 2.65 kg moist seeds were placed in each tray. During the drying test ambient temperature, ambient relative humidity, solar radiation, temperature at different points in the collector and drying chamber, air velocity at the outlet of the drying chamber, moisture content of seeds was recorded at one hour interval. Temperatures were measured at one hour interval by a digital temperature meter. Relative humidity was measured using a digital hygrometer. A digital solar meter was used to measure the solar radiation during the day time drying period. Velocity of drying air was measured with an anemometer. The moisture content of seeds was measured by oven dry methods at 105 °C for 24 hours.

A sample of approximately 20 g was evenly spread on a drying tray (0.25 m × 0.25 m) to form a single layer. Three layers (i.e. top and bottom layers) in the drying tray were used in the dryer. The data were recorded at hour interval from 9:00 a.m. to 9:00 p.m. Dryer test without load using electrical energy alone Dryer was tested without load using only electrical energy at FMPE Division, BARI, Gazipur on 7 May 2020. Five kilowatt electric heaters were used to heat air of the drying chamber. When temperature of the drying chamber raised up to 41-43°C, ambient temperature, ambient relative humidity, temperature at different points in the drying chamber, air velocity at the outlet of the drying chamber were recorded. Dryer test without load using solar energy alone Dryer was tested without load using only solar energy at FMPE Division, BARI, Gazipur on 8 May 2020. Collector was used to warm air temperature of the chamber. When temperature of the drying chamber raised up to 41-43°C, ambient temperature, ambient relative humidity, solar radiation, temperature at different points in the collector and drying chamber, air velocity at the outlet of the drying chamber were recorded. Dryer test with sweet gourd seeds using electric energy alone Dryer was tested with sweet gourd seeds collected from Joydebpur Chowrasta wholesale market. About 616 g of moist seeds were spread over the two trays (bottom and upper one) in single layer. A sample of approximately 5 g was evenly spread on a drying box (25 mm × 25 mm×10 mm) to form a single layer and two drying boxes used for each tray. Data were recorded at an hour interval from 10:20 a.m. to 4:30 p.m. (24 June2020) and 9.30 am to 2.20 pm (25 June 2020). Air temperature inside drying chamber was heated through electric heaters of 5 kW. When temperature of the drying chamber raised up to 41-43°C, trays were placed inside the drying chamber. Testing of seed quality of moist amaranth and sweet gourd seeds A germination tests were performed in FMPE Division, BARI, Gazipur. The working sample was separated into three components. (i) pure seeds (ii) other seed and (iii) inert matter. Each seed sample was used for germination test filter paper and sand. The standard germination test was conducted by placing seed samples on moist tissue paper and sand under ambient condition overnight in order to equilibrate with the ambient temperature and reduce the stress within the seed. Three replications of 100 seeds were taken for each sample. The samples were placed under room temperature to germinate. The seeds that had root or shoot longer than 2 mm were considered as germinated seeds. Modification of the dryer and fabrication of prototype Modification of the dryer was done during September to November 2019. To reduce the temperature difference among the trays, two dry heaters of 500 W capacity were vertically incorporated adjacent the upper two trays. A battery of 12 V was connected with two fans for running the fans when in absence of electricity or insufficient sunshine during drying operation. Battery is charged by controller through solar panel. A prototype of solar cabinet dryer was fabricated for demonstration and training among the seed growers for project area of Jashore during November 2019 to December 2019.

Source of Information: Annual Research Report 2019-2020, FMPE Division, BARI, Gazipur

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The moisture was reduced from an initial moisture content (17.76% wb) of red amaranth to the final moisture content of about 7.0% (wb) in 8 hours. The moisture content of sweet guard seeds was reduced from 41.59% to 9.23% (wb) in 6 hours of drying period. Germination of dried red amaranth and sweet guard seeds was found to be 93% and 98% respectively. Vegetable seed contract growers and farmers showed interest to use the dryer. Prototype of dryer was modified for taking efficient drying. A prototype of solar dryer was fabricated for demonstration in the project site.

Knowledge Management: Report/Proceedings