Drying technology
the collector can be large and thus heat greater quantities of air
Indirect dryers are, however, more expensive and complex to construct.
Practical Action
The obvious problem
with solar dryers is
their inability to work
when there is little or
no sunlight. The
McDowell dryer shown
in Fig 4 attempts to
overcome this problem
by combining solar
heat and heat from
wood burning in a fire
box. The Mc Dowell
dryer consists of a
block structure with a
fire box at one end.
Heat from the fire
passes through a metal
pipe below the tray of
food and exits via a
chimney. The whole
structure supports a
glazed solar roof.
3
Figure 3: Indirect solar
dryer
Figure 4: McDowell mixed dryer