Figure 1. The Picture Shows in the Foreground the Perforated Copper Plate of the Air Heater. In the Background, the 5 Lattice Wire Baskets can be Seen Hooked on Strings.


The drying box and the collector are built in a one piece enclosure covered with glass panels. The air heater (collector) is made of two absorber plates, one being a blackened corrugated iron plate, the other being a perforated copper plate, treated with a selective surface to increase its absorptive capacity for solar radiation and to reduce heat losses. The area of both the drying box and the air heater is one square meter each. Air circulation is achieved by either natural convection or a forced circulation provided by an electric fan. The product to be dried is put into lattice wired baskets, each one being hinged to a rigid rod fixed to the two side walls of the drying box section.

Dimensions : See Figure No. 2 and 3.

Materials of Construction:

Drying chamber

Tr ansparent cover: Frames: insulation: Trays:

Solar Air Heater:

Transparent cover:


Insulation: Frames•

glass of 3 mm thickness (plastic is good also) wood glass wool (wood shavings can be used) lattice wire baskets glass of 3 mm thickness (plastic sheet is also suitable)

one perforated copper plate treated with a selective surface under which is placed one corrugated iron plate painted matt black glass wool (wood shavings can also be used)


Location : Ankara, Turkey

Latitude: Longitude; Altitude: 900 meters above sea level

Climatological Data :

Sunshine hours :

Average annual radiation intensity:

Relative humidity:

Average ambient air temperature :

2700 hours - 64% of theoretical sunshine hours

3,5 Kwhr(m2 . day)with a maximum in July and a minimum in December. The difference between the maximum and minimum values of the radiation intensity during the year is about 4 ,65 Kwhr/( m2 .day)

varies from 20 to 80%

22°c in July, 3C>c in December

Practical Operation:

Number of units used in the past: four collectors with different areas and absorption plates tested

Nunfcer of units currently in use: three Periods of Operation of the unit:

(a) On experimental basis: July 1968 - November 1972

(b) in field operations: not reported

Drying Data;

Material apricot peach apple pear plum parsley mint aubergine pepper string beans

Pre-treatment halving and suplhuring cutting in 4 pieces and sulphuring peeling, cutting in 4 pieces, suplhuring peeling, cutting in 4 pieces, sulphuring washing, cleaning washing, cleaning washing, cleaning cutting no treatment cleaning, halving, blanching 5 to 10 minutes

Drying times are different for each material, it was found that peppermint had the shortest drying period (2 hours) and that the longest drying period occured with peaches and apricots (50 to 60 hours).

Operating Conditions;

The temperature increase in the drying box due to solar radiation intensity can be defined as follows; as proposed by the author.

y = -15,03 + 54,86x where x = is the average solar radiation intensity on the horizontal plane (cal/cm2 per minute)

y = is the temperature increase of the drying box for one hour with respect to the outside air temperature (oc)

The drying process was continued by forced circulation (fan) when the natural convection was too low inside the dryer. Even without the fan, the results were still satisfactory.

Economic Details; Cost of materials :

fan holed copper plate glass cover insulation wood frame labour

Annual Operating expenditure;

The cost of repair and maintenance work per year is about 4 percent of the unit's total cost.

Cost of drying related to a Unit of Material Dried:

Using the dryer 90 days per year, unit costs were about 0,30 Tl per Kg. (amortissement ratio 20%)

Estimated Life of the Dryer; 5 years

Comments on the Dryer:

increasing the capacity,the costs per square meter of useful drying space will decrease. It is thus advisable to use large capacity devices.

it might be still more economical to use local labour and locally available materials.

Principal Investigator(s): Mustafa Ozcan Ultanir

Ankara Universitesi Ziraat, Pacultesi Zirai Kuvvet Makilanair Kursusu, Aydinlikevler Ankara, Turkey



Overview :

Status : operational Type : chamber dryer

Operating mode : mixed

Air circulation: natural convection

This solar dryer is of simple construction and maintenance and utilizes readily available materials. The authors claim that the cost of dehydration per unit of dried products for this dryer is less than for all other known systems and techniques of drying. The quality of the dried product is preserved and the drying times are reduced significantly. The dryer is well suited for small and middle scale requirements.

Figure 1.

Views of the Orchard Solar Dryer cs/EC—L—1

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