Case Study I P



Status: operational Heating mode: indirect

Type: chamber dryer Air circulation: electric fan forced convection

This solar dryer, shaped as a triangular box, was specifically designed for the drying of herbs and spices which should be dried at a temperature not exceeding 43°C. The dryer is suitable for the requirements of a small community.

Air Inlet

Black Metal Plate

Transparent Cover ack cover

Air Inlet

Black Metal Plate

Transparent Cover

ack cover

Ground Level

Figure 1. Section View of Dryer

Ground Level

Figure 1. Section View of Dryer

Chara cter is tics:

The dryer is triangularly shaped and its collector has a 40° slope, inside the dryer is a set of drying drawers. The total surface area of the drying drawers is 9,29 square meters and there is also 1,5 m2 (16 sq.ft.) available for the drying of flowers. The drying chamber is not exposed to direct solar radiation, as the solar air heater covers it. The air heater itself consists of a clear plastic cover, a black metal plate absorber and a back cover. A 15 watt fan blows air through the air heater and dryer at a rate of 2,83 cu.m/min. (100 cu.ft/min.).

The air is admitted into the dryer through the upper back part of the collector by means of a fan. The fan blows the air on both sides of the black absorber plate of the solar collector, where it is heated and forced through the perforated bottom floor of the drying chamber. The air then rises through the drying racks on which the herbs are spread and is exhausted at the upper rear section of the drying chamber through openings provided for this purpose.

Dimensions t

The overall dimensions of the box are: 163 cm high (5'4"), 193 cm long (6*4"), and 122 cm wide (4'0")

Collector: 257 cm long (8'5"), and 122 cm wide (4'0") Vertical spacing of drying drawers: 4 cm

Materials of Construction: Drying Chamber:

Frames: wood

Insulation: none, as the temperature would get too high, destroying the herbs rather than drying them

Drying drawers: wood frame, 6,35 mm (V) mesh hardware cloth and vinyl window screen

Solar Air Heater:

Transparent cover: polyethylene sheet, 305 x 158 cm (5• x 10') and

Absorber: corrugated metal plate, 61 x 244 cm (10>sV x 3 •)

Frames: wood

Location: Santa Barbara, California, U.S.A.

Climatological Data:

Mediterranean type climate; the average tilted 40° towards the equator is:

incident solar energy on a surface March: 5,99 Kwhr/(m2-day) June: 5,52 Kwhr/(m2-day) Sept: 6,30 Kwhr/(m2-day) Dec: 5,36 Kwhr/(m2-day)

Practical Operation;

Number of units used in the past: none Nuxrber of units currently in use: one

Periods of Operation:

(a) On experimental basis: October 1973 to present

Drying Data:

Material Drying Time (days)

Basil 12

Rosemary 10

Orange bergamot mint 7

Lemon balm 8

Purple basil 6

Parsley 14

Green onion tops 2

Lavender 21

The tests reported in this study were undertaken during the winter season in California which is fairly mild, but has occasional rains lasting for a few days. The drying time is reduced by 50 to 75% in summer.

Operating Conditions:

This dryer has a thermostat fitted at the back of the solar absorber that automatically turns the fan on when the sun heats the plate.

The maximum interior operating air temperature should not exceed 43°C.

Economic Details:

Cost of Materials: Lumber

Hardware Electrical Sealing

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