Drying technology
Practical Action
Tent solar dryers, as shown in Figure 1, are cheap and simple to build and consist of a frame of
wood poles covered with plastic sheet. Black plastic should be used on the wall facing away from
the sun. The food to be dried is placed on a rack above the ground. Tent dryers provide protection
against rain, insects and dust and, in the case of fish for example, can reduce drying times by
25%. Tent dryers can also be taken down and stored when not in use. They have the
disadvantage of being easily damaged by strong winds
Figure 1: Typical tent solar dryer
The Brace solar dryer as shown
in Figure 2 has been widely
used for small scale food
drying. It consists of a wooden
box with a hinged transparent
lid. The inside is painted black
and the food supported on a
mesh tray above the dryer floor.
Air flows into the chamber
through holes in the front and
exits from vents at the top of
the back wall. Brace type dryers
achieve higher temperatures,
and thus shorter drying times,
than tent dryers.
Figure 2: Typical brace type dryer
A further design of solar dryer uses of a separate solar collector which supplies heated air to a
chamber containing trays of food. This is known as an indirect solar dryer and a typical design is
shown in Fig
3. Dryers of this type have several advantages over direct dryers which include:
the food is not exposed to the direct rays of the sun which reduces the loss of colour and
vitamins.
2