Integraltype

Integral-type, natural circulation, solar energy dryers are also called direct passive solar energy dryers. In this system, the crop is placed in a drying chamber,

Solar radiation

Solar radiation

Ambient air IN

Passive Solar Drying Principle Diagram

Moist air OUT

FIGURE 7.15 Schematic diagram of an integral-type passive solar dryer.

Moist air OUT

Ambient air IN

FIGURE 7.15 Schematic diagram of an integral-type passive solar dryer.

which is made with transparent walls; therefore, the necessary heat is obtained by the direct absorption of solar radiation at the product, from the internal surfaces of the chamber, and by convection from the heated air mass within the chamber. The heat removes the moisture from the product and, at the same time, lowers the relative humidity of the resident air mass, thus increasing its moisture-carrying capacity. The air in the chamber is also expanded because the density of the hot air is lower than the cold, thus generating natural circulation, which also helps in the removal of moisture, along with the warm air. Because heat is transferred to the crop by both convection and radiation, the rate of drying for direct dryers is greater than that for indirect dryers.

Integral-type, natural circulation solar energy dryers can be of a very simple construction, as shown in Figure 7.15, which consists of a container insulated at its sides and covered with a single glazing or roof. The interior walls are blackened; therefore, solar radiation transmitted though the cover is absorbed by the blackened interior surfaces as well as by the product, thus raising the internal temperature of the container. At the front, special openings provide ventilation, with warm air leaving via the upper opening under the action of buoyant forces. The product to be dried is placed on perforated trays inside the container. This type of dryer has the advantage of easy construction from cheap, locally available materials and is used commonly to preserve fruits, vegetables, fish, and meat. The disadvantage is the poor air circulation obtained, which results in poor moist air removal and drying at high air temperatures (70-100°C), which is very high for most products, particularly perishables.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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Responses

  • jason
    What is direct natural circulation?
    7 years ago
  • haile
    How to make a solar dryer diagram?
    7 years ago

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