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The resistance per wire length (Ω/m) of a heating element material is defined in ASTM and DIN standards. [2]: 2 [3] [4] In ASTM, wires greater than 0.127 mm in diameter are specified to be held within a tolerance of ±5% Ω/m and for thinner wires ±8% Ω/m.
Nichrome, a non-magnetic 80/20 alloy of nickel and chromium, is the most common resistance wire for heating purposes because it has a high resistivity and resistance to oxidation at high temperatures, up to 1,400 °C (2,550 °F). When used as a heating element, resistance wire is usually wound into coils.
Joule immersed a length of wire in a fixed mass of water and measured the temperature rise due to a known current flowing through the wire for a 30 minute period. By varying the current and the length of the wire he deduced that the heat produced was proportional to the square of the current multiplied by the electrical resistance of the ...
Nichrome (also known as NiCr, nickel-chromium or chromium-nickel) is a family of alloys of nickel and chromium (and occasionally iron [1]) commonly used as resistance wire, heating elements in devices like toasters, electrical kettles and space heaters, in some dental restorations (fillings) and in a few other applications.
Most modern electric heating devices use nichrome wire as the active element; the heating element, depicted on the right, uses nichrome wire supported by ceramic insulators. Alternatively, a heat pump can achieve around 150% – 600% efficiency for heating, or COP 1.5 - 6.0 Coefficient of performance , because it uses electric power only for ...
For heating, resistance wire must be stable in air when hot. Kanthal FeCrAl alloy forms a protective layer of aluminium oxide (). [1]Aluminium oxide has high thermal conductivity but is an electrical insulator, so special techniques may be required to make good electrical connections.