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air preheater[′er ‚prē′hēd·ər]
a heat exchanger for heating the air passing through it. Air preheaters are widely used in boiler installations of steam power plants and industrial enterprises, in industrial furnace units (metallurgical or petroleum-refining), and in hot-air heating, forced-air ventilation, and air-conditioning systems.
Hot, gaseous products of combustion (in boiler and furnace installations), steam, hot water, or electric power (in heating and ventilating systems) are used as the heat carriers.
Air preheaters are classified as recuperative or feed-water types according to the principle of operation. In recuperative air preheaters the heat exchange between the heat carrier and the air to be heated takes place continuously through the walls of the heating surfaces that separate them; in feed-water air preheaters the heat exchange is accomplished by the alternate heating and cooling of the metallic or ceramic nozzles of the fixed or rotating heating surfaces of the pre-heater. Tubular (steel or cast-iron) recuperative air preheaters, and less frequently rotating feed-water preheaters, are used mainly at thermal electric power plants. Periodic-operation feed-water air preheaters with a ceramic nozzle are widely used in the metallurgical industry. The air can be heated to 450°-600° C with metal units and to 900°-1200° C with ceramic-nozzle units.
I. F. LIVCHAK