Solar Drying: Fundamentals,Applications and Innovations - National ...

Visavale - Principles, Classification and Selection of Solar Dryers
and vegetables in regions without electricity. Figure 1.34 shows a hybrid solar dryer, a
modification of the dryer in Figure 1.35 with auxiliary source of heating. The ambient air
flows through a heat exchanger where it is heated to the desired temperature, by combustion
gas. Part of the used air is exhausted from the north wall of the dryer and the
rest is recycled through the recycling tube and the cooled gas exits through the chimney
to the ambient (Condori et al., 2001). Amer et al. (2011) has recently designed and evaluated
a hybrid solar dryer for drying of banana, consisting of a heat exchanger and heat
storage facility.
Figure 1.34. Features of a typical mixedmode
active solar-energy dryer
(Ekechukwu and Norton, 1999)
Figure 1.35. Solar tunnel dryer with an
additional auxiliary heat source
(Ekechukwu and Norton, 1999)
1.12. SELECTION OF SOLAR DRYERS
The diversity of food products has introduced many types and combinations of solar
dryers to the food industry. The methods of supplying heat and transporting the moisture
and the drying product are the basic variations among different types of solar
dryers. Table 1.2 enumerates the typical checklist for evaluation and selection for solar
dryers.
Table 1.2. Typical checklist for preliminary evaluation and selection of solar dryers
Sr.
no
Parameters
Features
1. Physical features of dryer
• Type, size and shape
• Collector area
• Drying capacity/loading density (kg/unit tray
area)
• Tray area and number of trays
• Loading/unloading convenience
2. Thermal performance
• Solar insolation
• Drying time/drying rate
• Dryer/drying efficiency
• Drying air temperature and relative humidity
• Airflow rate
3. Properties of the material • Physical characteristics (wet/dry)
Drying of Foods, Vegetables and Fruits 29