Air is used for drying materials which have moisture content, since ancient times. The moisture is taken away with the help of evaporative cooling. With the help of solar energy moisture is taken away from materials. It is used on a large scale for dehydrating agricultural products and foodstuffs.
Dehydrating can be done in two ways namely, natural convection and forced convection. In natural convection air is allowed to flow naturally without external source (like blower). In this heat is transported by siphon (density difference) in the fluid occurring due to temperature difference. While in forced convection blower or fan is used to increase the velocity of air which gives better results. In forced convection the rate of air flow increases eventually the rate of moisture absorbing capacity increases. There will be a comparison of the effects of natural and forced convection used in Solar Air dryer. The Solar Air Dryer consists of metal sheets, used to absorb solar energy which are called as absorber sheets. Three types of absorber sheets are used namely, flat sheet, lengthwise corrugated and width wise corrugated. There will also be a comparison of output quality given by three types of absorber sheets.
Solar air dryer is widely used for agricultural and industrial purposes. Drying foodstuffs by solar drying can increase the life of the product. This reduces wastage of foodstuffs also there is no use of conventional fuel. Successful drying depends on drawing out maximum moisture, flow rate of dry air to absorb the released moisture, and design of air circulation passage to carry off the moisture.