Distributed type

Distributed, natural circulation, solar energy dryers are also called indirect passive dryers. A typical distributed natural circulation solar energy dryer comprises an air heating solar energy collector, appropriate insulated ducting, a drying chamber, and a chimney, as shown in Figure 7.14. In this design, the crop is located on trays or shelves inside an opaque drying chamber, which does not allow the solar radiation to reach the product directly. Air, which is heated during its passage through an air solar collector, is ducted to the drying chamber to dry the product. Because the crops do not receive direct sunshine, caramelization (formation of sugar crystals on the crop surface) and localized heat damage do not occur. Therefore, indirect dryers are usually used for some perishables and fruits, for which the vitamin content of the dried product is reduced by the direct exposure to sunlight. The color retention in some highly pigmented commodities is also very adversely affected when they are exposed directly to the sun (Norton, 1992).

Higher operating temperatures are generally obtained in distributed natural circulation dryers than in direct dryers. They can generally produce higher-quality products and are recommended for deep layer drying. Their disadvantages are that the fluctuation in the temperature of the air leaving the solar air collector makes constant operating conditions within the drying chamber difficult to maintain; they are relatively elaborate structures, requiring more capital investment in equipment; and they have higher running costs for maintenance than integral types. The efficiency of distributed-type dryers can be easily increased, because the components of the unit can be designed for optimal efficiency of their functions.

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Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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