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Performance Evaluation of a BARI Solar Cabinet Dryer for Drying of Vegetables in Hilly Area (2019-20)

M M Morshed
Farm Machinery & Postharvest Process Engineering Division, BARI, Joydebpur, Gazipur, Bangladesh

M N Amin
Farm Machinery & Postharvest Process Engineering Division, BARI, Joydebpur, Gazipur, Bangladesh

M A Hossain
Farm Machinery & Postharvest Process Engineering Division, BARI, Joydebpur, Gazipur, Bangladesh

M R Ahmed
Farm Machinery & Postharvest Process Engineering Division, BARI, Joydebpur, Gazipur, Bangladesh

Abstract/ Executive Summary:

Sun drying is the most commonly used method to dry agricultural products. In sun drying, crops are exposed directly to the solar radiation, ambient temperature, wind velocity, relative humidity, etc. Rain, insect, human and animals interfere on this method. As a result, the products are contaminated. In hill areas of Bangladesh, various vegetables are produced. People of hill areas has the habit of eating dried vegetables. They usually sun dry their vegetables and store the dried vegetables for off-season consumption. In this reason, a solar cabinet dryer is needed in hilly area in Bangladesh to produce good quality, safety and nutritious dried vegetables products. A solar cabinet dryer was designed and fabricated at Farm Machinery and Postharvest Process Engineering Division, Bangladesh Agricultural Research Institute, Joydebpur, Gazipur under the project “Development and adoption of solar cabinet dryer for vegetable seeds” financed by KGF, Farmgate, Dhaka. It is an indirect solar cabinet dryer that consisted of drying chamber, collector and auxiliary heating source (electric heaters). Fresh radish (9.0 kg) was collected from farmers’ of Khagrachhari. The dryer was tested with the moist radish at Hill Agricultural Research Station, Khagrachhari during 17-18 February 2020. Drying temperature, relative humidity, air velocity and solar radiation were recorded. After drying, final weight of radish was 554 g. Inside air temperature of the drying chamber varied from 45.45 to 52.5 ^°C (first day) and 47.44 to 52.5 ^°C (second day). Air relative humidity in the drying chamber varied from 13.2 to 20.5 % (first day) and 11.53 to 18.5 % (second day), whereas the relative humidity in the ambient varied from 30.54 to 67.47 % (first day), and 42.25 to 65.25 % (second day). Collector outlet air relative humidity was found lower than the ambient air relative humidity. The global solar radiation varied from 50 to 900 W/m² during testing period. Fresh radish dried in the dryer attained final moisture content of 9.0 % (wb) from an initial moisture content of 94 % (wb) after 11 hours of drying period whereas, it took fifty six hours to reduce the moisture content to 12 % (wb) of similar sample in open sun. In open sun drying method 9.0 kg moist radish was dried to 380 g. In open sun drying method radish losses by 30 % during drying as a result of fungus’s infestation. The capacity of the dryer was 18-20 kg/batch. Color of dried slices in dryer was more bright and smell was good compared to sun drying of radish slices. The dryer maintained nutrition and made hygienic and safe products of radish slices. Hilly farmers and small scale traders would be benefited using the BARI solar dryer.

Keywords: Solar cabinet dryer, Drying vegetables, Radish, Hill areas

Location: FMPE Division, BARI, Gazipur and Hill Agricultural Research station, BARI, Khagrachari

Start Date: 00-00-2019

End Date: 00-00-2020

Program Area: Farm Mechanization

Commodity: Drier, Radish

Objectives:

a. To evaluate the performance of BARI solar cabinet dryer for drying of vegetables, and

b. To compare the economic benefit between BARI solar cabinet dryer and conventional method for drying vegetables.

Methodology:

Description of the dryer: Design of the indirect solar cabinet dryer for drying of vegetables was done based on the energy balance and heat and mass balance equations. The dryer consisted of a concentrating type flat plate collector, 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 of at night using auxiliary electric heaters. The length, width and height of the drying chamber were 0.84 m, 0.81m and 1.73 m respectively and length, width and height of the collector were 2.30m, 1.22 m and 0.33 & 0.14 m respectively. Drying chamber: Drying chamber consisted of tray, heater, and inlet and outlet fan. Six drying trays were placed in the drying unit. The dimension of the drying tray was 0.08 m × 0.745 m × 0.0488m. The stainless iron mesh was used and mesh number was 20. The drying air was passed through the products. Each tray was of metallic frame and stainless iron net with dimensions of 1040 mm × 780mm. The drying air was heated up in the collector and passed to the drying chamber trough a curved passed at the end of the drying unit and flew over and under all the drying trays and exhausted from the outlet. For auxiliary heating, two electric heaters each of 2.5 KWcapacities were installed at the bottom of the drying chamber. A temperature controller was set to maintainconstant temperature in the dryer. Two small dc fan (each of 5W) were used for air flowing in the dryer operated by a small solar panel (25W) and in absence of solar energy it is operated by alternative current (electricity). A 5 W axial flow fan was connected in outside of the collector to draw the atmospheric air in the collector and to push out the heated air to the drying chamber with a desired air velocity. Another 5 W axial flow fan was located at top of the drying chamber. A temperature controller was set to maintain temperature in the dryer. Collector: The collector was fabricated with transparent polyethylene sheet, corrugated iron sheet, MS flat bar, wood, MS angle bar, overall dimensions of the flat plat plate concentrating solar collector are 2.30 m long and 1.22 m wide. The transparent cover of the collector was2 mm thick clear plastic sheet. About 1 mm black painted corrugated iron sheet is used as and absorber plate. The collector was placed on 4 legs with 140 mm diameter wheels to turn the solar collector horizontally and change its direction according to the change of the sun’s angle. Testing procedure: The dryer was placed in a sunny place so that it was not affected by shadow.The dryer was tested for drying of radish. Freshly harvested radish was purchased from farmer of Khagrachari and sliced by manual (by knife).Nine kilogram of sliced radish spread on three trays of dryer. Similar sample of sliced radish placed in the open sun for comparison with solar dryer.Ambient temperature, ambient relative humidity, global solar radiation, temperature at different points in the collector and drying chamber, air velocity at the outlet of the drying chamber, moisture contents of radish sliceswas recorded at one hour interval. Temperatures were measured at one hour interval by a digital temperature meter (model: k 102, accuracy ± 0.3%, Conrad Electronics, Germany). Relative humidity was measured using a digital hygrometer (Model: MY-91HT, 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 drying period. Velocity of drying air was measured with an anemometer (Model: TA430, accuracy ± 3% Airflow Ltd., England). The moisture content of radishslices weremeasured by oven dry methods. Three layers (i.e. top, middle and bottom layers) in the drying rack were used in the dryer. The data were recorded at 1 hour intervals From 9.00 am to 17:00 pm. The capacity and sensitivity of Shimadzu electronic balance (ELB- 3000, Japan) used were 3000g and 0.1g, respectively.

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

Article Link (Online Journal):

Funding Source:

1. Krishi Gobeshona Foundation

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Performance of a BARI solar cabinet dryer was evaluated with moist radish slicesat Hill Agricultural Research station, Khagrachari. Nine kilogram moist radish was used and it reduced to 554 g. Drying temperature in the drying chamber was maintained to be 45.45 to 52.5 during the drying period. Ambient relative humidity in the drying chamber varied from 11.53 to 20.5 %.The solar radiation varied from 50 to 900 W/m² during testing period. Moisture content of the radish reduced from 94 % to 9.0% (wb) in 11 hours of drying whereas, it took fifty six hours to reduce the moisture content to 12 % (wb) of similar sample in open sun. In open sun drying method 9.0 kg moist radish become 380 gm after drying. The dryer should be used for drying of hygienic, safety and nutritious radish slices. Hilly farmers and small scale traders would be benefited using the BARI solar dryer.

Knowledge Management: Report/Proceedings