Closed cooling tower coil is actually closed cooling tower internal heat exchanger. Through a series of thin tube bundle increases the heat transfer area, making the medium inside the tube and tube heat exchanger water spray. It can also be seen as a special form of tubular heat exchanger. Typically there are several tube outer diameter specifications, 12mm, 16mm, 19mm, 22mm, 26mm and so on. 16mm and 19mm are more common. There are a variety of tube materials, usually T2 copper, 304 stainless steel, 316 stainless steel, carbon steel pipes, rust aluminum and other materials. Where T2 copper and stainless steel pipe use more. Some special conditions, require special materials produced coil. For example, sulfuric acid cooled, general corrosion of the material will be only made ​​of titanium heat exchanger tube can withstand.