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Tunnel Solar Food Dryer |
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| Description |
4 ft x 8 to 16 ft tunnel solar food dryer, adapted from the Hohenheim tunnel solar food dryer design |
| Primarily For
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Agriculture |
| Other Purposes
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Agriculture, Economic Development |
| Climate |
Dry/Arid, Temperate |
| Emphasis |
Communities, Individuals |
| Effort to Implement
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Moderate |
| Maximum Cost |
$
0 |
| Why |
Tunnel solar food dryer ver 3/2008
I. Solar food dryer design
This tunnel solar food dryer design is a scale down version of the tunnel solar food dryer developed at University of Hohenheim, Stuttgart, Germany (www. innotech-ing.de). The dryer dimension is 4 ft wide x 16 ft long x 12 to 19 inches tall (1.2 m x 4.9 m x 0.3 to 0.48 m) and is constructed with materials readily available in US (Figures 1 to 4). The frame consists of two 4 x 8 ft plywood sheets and 1 x 4 inch side boards (Figure 3). Hoops made of 9 gauge (3.8 mm) wires support a clear polyethylene film cover (Figures 2, 5 and 6a). The peak height of the polyethylene cover is 8 to 16 inches (20 to 41 cm) above the drying trays. One edge of the polyethylene film is securely attached to the side of the frame while the other is attached to a 1 inch polyvinyl chloride (pvc) pipe. The pvc pipe allows the cover to be moved for easy access to the drying trays (Figures 1 and 2). The bottom of the dryer is insulated with two 3/4 inch x 4 ft x 8 ft foil faced insulation board (Figure 4 and 5). The entire solar dryer frame is supported on a swivel and tilt bracket (Figures 7 and 8), allowing the dryer to rotate and tilt for maximum sunlight exposure.
A smaller version of this dryer, 4 ft wide x 8 ft long x 10 inches tall can be constructed by using one 4 ft x 8 ft plywood sheet and one 3/4 inch x 4 ft x 8 ft insulation board (Figure 4). This smaller dryer will accommodate two 3 ft x 4 ft drying trays or one 4 ft x 6 ft tray.
Dryer trays
Drying trays, 4 ft wide x 6 ft long or 3 ft x 4 ft are made by attaching knitted polypropylene shade cloth to the bottoms of 3/4 x 1 1/8 inch wood frames (Figures 5 and 6a). These drying trays are set on interior tracks that raise the trays ~2 inches above the bottom of the tunnel dryer. Trays are held in place by top braces to prevent the trays from sliding on the tracks when the dryer is tilted. Air ducts convey heated air from the solar collector section to below the drying trays, allowing heated air to rise through the bottom of the polypropylene shade cloth (Figure 6a and 6b).
Variable settings for solar dryer
Optimize the solar dryer by adjusting the peak height of the polyethylene cover, tilt angle of the dryer, and amount of produce placed in the dryer. The height of the polyethylene cover adjusted the volume of heated air, resistance to airflow and the path of airflow, traversing high above the trays or closer to the trays. The tilt angle of the dryer adjusts the airflow rate. The amount of produce placed in the dryer affects the humidity in the dryer and the rate of drying.
In the Willamette Valley of Western Oregon, daytime temperatures range from 80-90F (27-32C) with a 15-35% relative humidity and a variable 0 to 5 mph (0-2.2 m/s) wind. In a 4 ft x 16 ft dryer, with -
* a 10 inch peak height above the drying tray,
* 3 degree tilt angle, and
* two 4 ft x 6 ft drying trays filled with fresh tomatoes,
the temperature above the drying trays ranged from 100-120F (38-49C) with a relative humidity between 15-30%. After 6 hours of drying, 40 pounds (18 kg) of fresh tomatoes were reduced to 22.5 pounds (10.2 kg)-a 43% weight reduction. The partly dried tomatoes were used to make tomato sauce.
Allen Dong, I-Tech, PO Box 413, Veneta, OR 97487, USA
Public domain, no copyright
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| URL(s) |
http://www.efn.org/~itech/Tunnel%20solar%20dryer/0803%20Tunnel%20solar%20dryer.html
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| Availability Limits |
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| Resources |
Complete instructions on listed url |
| Email |
Withheld |
