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air duct[¦er ‚dəkt]
a device in the form of a pipe for the movement of air; used in ventilation, hot-air heating, and air-conditioning systems, and for special industrial applications (supplying air to industrial units, removal of waste products from machines and equipment, movement of bulk materials in pneumatic conveyor systems, and so on). Interconnected air ducts that serve a specific system form a duct system, which consists of straight and curved sections that make possible changes in direction, convergence, branching, and widening or narrowing of the air flows. Air ducts have round or rectangular cross sections and are made of steel, asbestos cement, concrete, brick, cinder plaster, vinyl plastic, polyethylene, or other materials. Ventilation systems have separate supply and exhaust air ducts.
Air ducts are installed in spaces beneath ceilings (overhead ducts), along walls (wall-mounted ducts), and in attics or lofts (attic ducts) or are built into the structure. Air ducts are equipped with valves to control the quantity of air in the system. The movement of air in a duct is associated with the energy consumption required to overcome frictional resistance (encountered along the entire length of the duct) and local resistance (such as that caused by duct fittings). The amount of resistance depends on the structure of the inner surface of the duct, the parameters of the curved parts, the velocity of the air flow, and the sizes of the air ducts.
REFERENCESIdel’chik, I. E. Spravochnik po gidravlicheskim soprotivleniiam. Moscow-Leningrad, 1960.
Maksimov, G. A. Raschet ventiliatsionnykh vozdukhovodov. Moscow-Leningrad, 1952.
Spravochnik po teplosnabzheniiu i ventiliatsii, 3rd ed., part 2. Kiev, 1968.
T. A. MELIK-ARAKELIAN