The mixed-mode dryer is similar to the distributed type with the difference that the walls and roof of the dryer are made from glass, to allow solar energy to warm the products directly, as shown in Figure 7.13.
It should be noted that, because drying efficiency increases with temperature, in conventional dryers the maximum possible drying temperature that would not deteriorate the product quality is used. In solar dryers, however, the maximum drying temperature is determined by the solar collectors, because their efficiency
decreases with higher operating temperatures and this may not yield an optimal dryer design.
Most air heaters use metal or wood absorbers, whereas black polythene absorbers have been used in a few designs in an attempt to minimize cost.
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