The solar dryers have been classified according to their heating modes, or the manner in which the heat derived from the solar radiation is utilized. In this regard, several general categories have been set up which are defined below. At the top of each case study, several descriptive terms have also been listed in order to classify the solar dryer and its operations. These terms have also been defined below. In general, a dryer has been classified according to its principal operating mode. Some of the direct and mixed mode dryers also use circulating fans, and are strictly not totally passive systems.
SOLAR DRYER CLASSIFICATIONS;
- Passive Systems - dryers only using solar or wind energy for their operations.
SUN OR NATURAL DRYERS:
These dryers make use of the action of solar radiation ambiant air temperature and relative humidity and windspeed to achieve the drying process!
SOLAR DRYERS - DIRECT;
In these units, the material to be dried is placed in an enclosure, with a transparent cover or side panels. Heat is generated by absorption of solar radiation on the product itself as well as on the internal surfaces of the drying chamber. This heat evaporates the moisture from the drying product. In addition, it serves to heat and expand the air in the enclosure, causing the removal of this moisture by the circulation of air.
SOLAR DRYERS - MIXED MODE; (Direct and Indirect)
In these dryers, the combined action of the solar radiation incident directly on the material to be dried and air pre-heated in a solar air-heater furnishes the heat required to complete the drying operation.
- Hybrid Systems - dryers in which another form of energy, uch as fuel or electricity is used to supplement solar energy for heating and ventilation.
SOLAR DRYERS - INDIRECT; (with forced ventilation)
In these dryers, the solar radiation is not directly incident on the material to be dried. Air is heated in a solar collector and then ducted to the drying chamber, to dehydrate the product.
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