Radiant Tube

a heater consisting of a tube made of either high-temperature steel or corundum, in which a gaseous (or sometimes liquid) fuel is fired. Heat is transmitted by radiation from the outer surface of the heated tube to the articles being heated. Radiant tubes are installed in furnaces used for the heat treatment of metal articles that must not come into contact with the combustion products of fuels (heating in controlled atmospheres or in air). Tubes made of metal are used for heating articles up to 950°C; those made of corundum are used for treatment up to 1200°C. The diameter of the tube varies from 60 to 200 mm, and the length of each branch may be up to 2.5 m.

Radiant tubes are classified according to their construction. The simplest is a vertically or horizontally positioned straight tube with a burner mounted at one end and an outlet for combustion products at the other. Improved types of multibranch radiant tubes, designed to recover the heat of the combustion products, are shown schematically in Figure 1.