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Drying of Mango Using Solar Tunnel Drier

B.K. Balal
Bangladesh Agricultural University, Mymensingh-2202,

M.R. Mondol
Bangladesh Agricultural University, Mymensingh-2202,

B.L. Das Choudhury
Bangladesh Agricultural University, Mymensingh-2202

Abstract/ Executive Summary:

Field level experiments on solar drying of mango using solar tunnel drier were conducted at Chapai Nawabganj, Bangladesh. The drier consisted ofa transparent plastic covered flat plate collector and a drying tunnel connected in series to supply hot air directly into the drying tunnel using two dc fans, operated by a solar photovoltaic module. This drier has a loading capacity of 120-150 kg ofmango. A total of9 drying runs were conducted. Drying air temperature at the collector outlet varied from 35.6°C to 53.5°C in the months of July and August, 1999 and 35.9°C to 56.7°C in the months of June and July 2000. The temperature inside the collector increased along the length ofthe collector from the inlet ofthe collector while the drying air temperature was almost constant throughout the drier length during drying of mango. The moisture content ofthe sulphur treated mango of a typical experimental run reached 13.47% from 78.87% in 3 days ofdrying in the solartunnel drier while ittook 3 days of drying .to bring down the moisture content of similar sample to 22.48% in traditional method. Proximate analysis indicated that the mango dried in the solar tunnel drier was a good quality product for human consumption.

Keywords: Drying, Mango, Solar Tunnel Drier, Bangladesh

Location: Mango Research Centre, Chapai Nawabganj, Bangladesh

Start Date: 00-07-1999

End Date: 00-07-2000

Program Area: Postharvest and Agro-processing

Commodity: Mango

Objectives:

The purpose of this research was to study the performance of the solar tunnel drier for drying of mango slices under Bangladesh condition.

Methodology:

The drier consisted of a flat plate air heating collector, a tunnel drying unit and a small fan (Taiwan made 6" diameter, dc 12 V, 1.2 A) to provide the required air flow over the product to be dried. These are colmected in series. Both the collector and the drying unit are covered with plastic. Black paint is used as an absorber in the collector. The products to be dried are placed in a thin layer on a bamboo split net in the tunnel drier. Glass wool is sandwiched inside the floor of the drier to reduce the heat loss from the drier. The whole system is placed horizontally on a raised platform. The air at required flow rate is provided by two dick fans operated by one photovoltaic module (Solarex: 12 V, 41.6 W). As the air is passed over the product rather than through the product in the drier, the power requirement to drive a fan is low (14.4 W). To prevent the entry of water to the drier unit during rain, the cover is fixed like a sloping roof. Solar radiation passes through the transparent cover ofthe collector and heats the absorber. Ambient air is forced through the collector. Heat is transferred from absorber to air in the collector and heated air from collector while passing over the products absorbs moisture from the products. Solar radiation also passes through the transparent cover of the drier and heats the products in the drier. This enhances the drying rate and the temperature rise in the drier is in the ranges of35.6 °C to 56.7⁰c. Experimental procedures The solar tunnel drier was installed at the Mango Research Centre, Chapai Nawabganj, Bangladesh. The drier was placed on raised platforn,! and it was not shaded by trees or building during 8.0 am. to 4.0 pm. Nine full scale experimental runs on solar drying of mango w'ere carried out in the months of July and August, 1999 and June and July, 2000. Important parameters affecting the perfom1ance of the drier were measured. A k-type the mlo-couple was used to measure the drying air temperature along the flow direction of the air inside the drier and a pyranometer (photovoltaic Solar cell type) was used to measure the global radiation at the inlet of the drier.

Experimental solar drying runs were conducted on two varieties of mango. These varieties were Khirsapat and Fazli. Mango slices of 10 rom thickness were treated with sulfur dioxide by burning sulphur in a sulphuring box @40 mg ofelemental sulphur per kg offresh mango slices for 30 minutes. Mango slices were then spread on bamboo split structure in a thin layer. For each ofthe experimental runs the drier was loaded to the full capacity of 150.0 kg of mango. The drying was starteeJ usually at 0090 hand discontinued upto 1600 h for each day. To compare the performance of the tunnel f drier with that of the sun drying, control samples ofmango slices were placed on trays in a single layer on a raised platform beside the drier. Both experimental and control samples are dried simultaneously under the same weather conditions.

Source of Information: Journal of Agricultural Engineering Vol. 38(1): 7-13: January-March, 2001

Article Link (Online Journal):

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Field level drying of mango slices was conducted. The temperature ofthe drying air at the collector outlet varied from 35.6 °C to 56.7°C during drying. This drier can be used to dry up to 150 kg of fresh mango. The mango dried in the solar tunnel drier was completely protected from rain, insects and dust, and the dried mango was a high quality product. . This drier is simple in construction and it can be constructed using locally available materials by the local craftsman. The solar tmmel drier can be operated by a photovoltaic module independent of electrical grid. The photovoltaic driven solar tunnel drier must be optimized for efficient operation.

Knowledge Management: Journal