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Electric Heating

Electrical heatings have been used in the field of production in various industries. The benefits, in comparison to heaters that use fluid for heat distribution, are faster response, higher maximum temperaturesa and a more cost-effective realization.

 

Conventional resistance wire has a high specific resistance - and because of

a high specific thermal production. The conductor area is small, this means the temperature gradient falls steeply from the heating wire to the heated medium. The result: an inhomogeneous heating with large temperature variations. Heat conduction plates between the heating wires and the heated surface mean a slight improvement, as they distribute the heat parallel to the surface. On the other hand, disadvantages are loss of efficiency and increasing inertia of the heating, because every heating-up means to heat the entire mass.

 

Why copper is the ideal material for heating wire

Copper has a low specific electrical resistivity. An adequate heating resistor can be achieved by small conductor cross-sections and long conductor lengths. Copper is superior to other heating wire materials thanks to best thermal conductivity and low heat capacity providing an excellent control behavior. Furthermore, the risk of conductor fracture is small because of the high ductility.

 

CoTexx® Knitted Heating Fabric consists of litz wire, as used in electrical engineering. The wire drawing process ensures a constant small conductor cross-section and a resulting constant resistance per length. These strands are enamelled to isolate them from each other and combined to form the litz wire.

 

Due to their excellent properties litz wires have become standard in (automotive) seat heaters. For this purpose, the litz wires are stitched onto a backing fabric in a meandering shape.

 

Advantages of Litz Wire

  • constant resistance per length
  • ageing stability
  • ductility
  • PTC-characteristics prevent overheating
  • many individual strands for high redundancy
  • hot spots physically impossible

 

Hot spots, meaning local temperature peaks caused due to conductor break, are impossible.The following graphics illustrate this using the electrical equivalent circuits:

Normal wire with one broken strand

Litz wire with one broken enamelled strand

Equivalent circuit after conductor break:
hot spot at the cross-section constriction

Equivalent circuit after conductor break:
still homogeneous heat generation

If a strand brakes in a normal litz, like in extension cables, the result is a locally higher electrical resistance and thus a hot spot on the site of fracture.
If, however, an enamelled strand of a litz wire breaks, there is no current flow in this strand. The other strands are independent, thus the heat production is constant. The total resistance of all 120 parallel strants will increase slightly. Therefore, the voltage has to be slightly adjusted to produce the same heating power.

 

Why heating "fabric"

CoTexx® Knitted Heating Fabric consists of litz wire. Knitting positions the heating conductors in an orderly manner. Furthermore, a high deformability / drapability is achieved, which is characteristical for knitted fabrics.

Feel free to contact us for further information
hotline: 0800 6677373
telephone: +49(0)8259 8287-81
info@cotexx.com