Operating conditions t

It was observed that an average temperature of 75°C was attainable inside the dryer as compared to an average outside temperature of 35°.

3 4 Drying Hours Heures de Séchage

Figure 2. Drying Characteristics of Fruits and vegetables

Courbes Comparatives pour le Séchage des Fruits et Légumes

A) Prunes

B) Cauliflower - choux-fleur

Drying Hours Heures de Séchage

3 4 Drying Hours Heures de Séchage

Figure 2. Drying Characteristics of Fruits and vegetables

Courbes Comparatives pour le Séchage des Fruits et Légumes

A) Prunes

B) Cauliflower - choux-fleur

0 inside the Solar Dryer - Dans le Séchoir Solaire # Under the Open Sun - Séchage au Soleil

Economic Details;

Cost of materials« (refer to sketch)

Item Nunber of pieces Dimensions Total Cost required Rupees

Glass sheet 3 61 x 62 cm 30,00 Indian chir

Plywood sheet 2 198 x 66 cm 16,00

Aluminum sheet 2 2456 cm 8,0C

Mesh for trays 3 62 x 62 cm 25,00

Polythene pipes 25 12,7 disaster x 6 cm long 2,00

Miscellaneous - - 5,00

Labour charges 2 days - 12,00

Annual Operating Expenditurei

Depreciation of the unit per year 16,00 Rs interest on capital (at 10%) 16,00 Rs

Contingencies 8,00 Rs

TOTAL 40,00 Rs

Cost of drying related to a Unit of Material Dried;

The researchers estimated this cost to be about 20% of the cost of the raw material.

Estimated Life of the Dryer» 10 years Comments on the Dryert

It is found that solar drying saves considerable tins. Also the final product quality obtained front the dryer was found to be superior in taste and odour without being contaminated by dust and insect infestation.

Principal investigator(s): Agrawal, h.C.

Indian institute of Technology Department of Mechanical Engineering Kanpur, uttar Pradesh India

Note; The unit described is based on the design presented in Case Study No, E.




Status: experimental Heating mode: direct

Type: chamber-tray dryer Air circulation: natural convection

The see-saw dryer was originally developed in the ivory Coast for the drying of coffee and cocoa beans. Its design was further refined under work sponsored by the Government of Ghana and the Food and Agriculture Organization (FAO) of the united Nations. This simple dryer is suitable for small-scale drying operations and can be easily operated, its use is envisaged for tropical regions. The dryer can be operated in a simple manner in two positions along a central axis of rotation running north-south. This see-saw operation permits the drying material to face the sun more.directly during both the morning and the afternoon. This increases the output of the unit and leads to a more evenly dried product. Specifications and plans are included.


The see-saw dryer consists of a rectangular wood frame divided lengthwise into parallel channels of equal width, and crosswise by means of retaining bars. The bottom of the dryer frame is made of bamboo matting painted black and receives the material to be dried. The cover of the frame is made of a film of transparent Polyvinyl Chloride (P.V.C.) which provides a substantial screening effect against ultra violet light, thus reducing photo degradation of the drying product. All of the internal parts of the dryer are coated with a matt flat black paint. The drying tray is moved during operation in an east-west ptwrre. It is mounted on a trestle whose height is equal to one«fourth of the frame length. The drying frame can then be tilted and fixed to face the sun in the east during the morning and to face west during afternoon. The effective area of the dryer is limited by two transverse retaining bars fixed at 200 mm from each end of the drying frame and two others set 300 trro apart, about the transverse central line of the drying frame. The three small black bands thus delimited by the retaining bars are left free from any drying product and their purpose is to convert the radiant energy from the sun into heat. The heated air is circulated by natural convection from the lower to the upper end of the dryer by means of gaps provided at each end of the frame. Additional air is drawn through the matting base of the dryer by the natural convective effect as well. Produce to be dried is loaded with the dryer in a horizontal position, up to the level of the crosswise retaining bars, allowing clearance under the cover in order to permit air flow.

Dimensions: The overall dimensions of the rectangular drying frame are 3,6 meters long, 1,2 meters wide and 80 rrcn deep. According to the authors, the dimensions of the dryer are optimized as a result of their own studies. Refer to the set of plans included, Figure NOS. 4 to 11.

Materials of Construction:

Frame and trestle: wood

Drying rack (frame bottom): bamboo matting or thin wood strips woven with rope Transparent film cover: P.V.C. sheet 0,3 mm thick Location:

Tested in Ivory Coast, Cameroon and Malagasy, countries located in the tropics, where the dryer can be best used without any modifications to the plans included in this study.

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