Solar air heaters

Solar air heaters find extensive applications in agricultural, industrial and domestic fields. A solar air heater is composed of an absorber plate and another plate parallel to it with a small passage in between. The air which is to be heated is allowed to pass through this gap. A transparent cover system is placed above the absorber plate. On the bottom and the sides of the heater, a sheet metal container filled with insulation is fixed. The design of solar air heater is very simple and can be maintained even at temperatures below zero degrees Celsius. Loss due to corrosion and leakage is negligible here but heat transfer coefficient value is very low which results in a lower efficiency. To improve efficiency, some modifications are suggested. They are roughening the surfaces, providing longitudinal fins in the air-flow passage and usage of V-shaped or corrugated absorber plate. Since large volumes of fluid have to be handled here, electrical power requirement is more. The face areas of solar air heaters range from 1 to 2 square meter. Absorber plate is made of galvanized iron or steel with 1mm thickness. Glass is the most favored choice for cover material with some 4 to 5 mm in thickness. For the insulation of bottom and side parts, mineral wool or glass wool is employed. The whole system is assembled in a sheet metal box which is inclined at a suitable angle.