Properties of Heating Material

The heating element should have following properties.
High specific resistance
  • As the specific resistance of the material should be kept high, the length of material requires for particular resistance is short.

        R = ρL / a
       Where ρ is resistivity of material
High melting point
  • The melting point of the heating material must be high so it can withstand higher temperature.

Low temperature co – efficient
Heat dissipated according to Stephen’s law
H = 5.72 ke[ ( T1 /100 )4 – ( T2 /100 )4  ] ………… ( 1 )
  • If the material has low temperature co – efficient, it means that there is small variation in the resistance with respect to change in the temperature therefore the current drawn by the heating element is approximately same during hot and cold conditions.

Positive temperature co – efficient
  • If the temperature co – efficient of the heating material is negative, the resistance of the material decreases as the temperature increases therefore the heating material will draw more current and more heat. 
  • As the heat increases, the resistance of material decreases and it will result in instability of operation.

High oxidizing temperature
  • The oxidizing temperature of the material should be high in order to long life. The oxidation of material should reduce the life of heating material.

  • The heating material should have high ductility and flexibility in order to form convenient shape.

Mechanical strength
  • The heating material should have higher mechanical strength in order to withstand against temperature. The maximum withstand capability of silicon carbide is 1450 oC ,Kanthal is 1200 oC , Nichrome is 1150 oC and constantan is 400 oC.

Non – corrosive
  • It should be non – corrosive.

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