Resistance type electric heating elements

Electrical resistance boilers use banks of fixed, immersion-type, resistance heating elements (typically sheathed in seamless copper, Incoloy 800, or 316SS) to provide an energy source that is contained within a carbon-steel pressure vessel. The vessel is provided with a sight glass and all normal boiler controls, valves, and regulators necessary for automatic operation. The vessel is generally well insulated and housed within an enameled metal cabinet. Various electrical supply options are available. 

For continuous melting of domestic and technical glass, small electric furnaces have been developed a longitudinal cross section of one such type is shown in Fig. 102. At the working end, the temperature is controlled by resistance heating elements. The direction of melt flow is shown by the arrow. All-electric furnaces have to be heated up by auxiliary gas burners since the cold batch does not conduct electrically. 

Electric Resistance Heating - A type of heating system where heat, resulting when electric current flows through an "element" or conductor, such as Nichrome, which has a high resistance, is radiated to a room. 

Never use a furnace like a black box. The heating elements will go to certain temperatures, but even then you may not want that type of material close to your sample to minimize contamination. Table 9.4 lists the materials used for electrical resistance heating. 

We will now look, in a little more detail, at some of the ceramic materials that are used as heating elements in furnaces. We will also mention one other type of resistance element, SnOi, which is used in electrically heated glass-melting furnaces. 

The short-wave IR radiation can only be generated by an electric IR heater employing a tungsten heating element. A tungsten filament has small mass as well as low electrical resistance, which allows heavy current flow and very rapid heat up and cool down. The rate of response of various types of radiant heat sources can be an important criterion in the selection of a proper source for coating drying applications. 

The single-storage heater is heated by an electric element embedded in bricks and rated between 6 and 15kW depending upon its thermal capacity. A radiator of this capacity must be supplied on its own circuit, in cable capable of carrying the maximum current demand and protected by a fuse or miniature circuit-breaker (MCB) of 30, 45 or 60 A as appropriate. At the heater position, a DP switch must be installed to terminate the fixed heater wiring. The flexible cables used for the final connection to the heaters must be of the heat-resistant type. 

Carbon fiber is brittle material made from organic fibers through a series of heat treatment and contains carbon content of more than 90%. When the carbon content is over 99%, this type of carbon fiber is called graphite fiber. Carbon fiber has excellent properties of carbon element, such as low density, good heat resistance and exeeUent thermal expansion coefficient, thermal conductivity coefficient, good corrosion resistance and electrical conductivity and so on. At the same time, it is also soft like fiber, and can be weaving and winding. 

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