Electrically produced heat possesses the following advantages over other forms of
Heat:
i. Cleanliness: The complete absence of dust and ash keeps cleaning cost to a
minimum.
ii. High efficiency of utilization : Practically 75% to 100% 0f heat produced can be
utilized.
iii. Absence of fuel gases : No fuel gases produce.
iv. Ease of control : Simple and accurate control of temperature can be provided.
v. Low attention and maintenance costs: Electric heating equipments require no
attention, while maintenance costs are negligible
Various types of Electric heating and their applications:
i. Resistance heating: Two methods are employed in resistance heating.
a. Direct resistance heating: In this method , the material or charge to be heated
is taken as a resistance and current is passed through it. Resistance and current
is passed through it. The charge may be in the form of powder, pieces or
liquid. The two electrodes are immersed in the charge and connected to the
supply.
b. Indirect resistance heating: In this method the current is passed through a high
resistance element which is either placed above or below the oven depending
upon the nature of the job to be performed. The heat proportional to I2R losses
produced in the heating element is delivered to the charge either by radiation
or by convection.
Applications: Resistance heating is used in heat treatment of metals like
annealing and hardening etc., stoving of enameled wires, drying and baking of
pottery and commercial and domestic cooking.
ii. Induction heating:
Induction heating processes make use of currents induced by electromagnetic action
in the material to be heated. Induction heating is based at the principle of
transformers, there is primary winding through which an ac current is passed. The coil
is magnetically coupled with the metal to be heated. An electric current is induced in
this metal when the ac current is passed through the primary coil.
Applications:
• Surface hardening
• Deep hardening
• Tempering
• Soldering
• Melting
• Smelting etc.
iii. Dielectric Heating : for the heating of non metallic material i.e. insulators such as
wood, plastics, the dielectric loss occurs in such materials when subjected to an
alternating electrostatic field. The material to be heated is placed between two
metallic electrodes across which a voltage is applied. To ensure sufficient heating an
adequate amount of heating frequencies between 10MHz and 30MHz must be used
and the voltage needed may be as high as 20kV.
Applications:
• Seaming and welding in manufacture of synthetics.
• In wood processing industry.
• For baking foundry cores.
• For food processing.
iv. Arc Heating :
If an air gap is subjected to a very high voltage , the air in between gets ionized due to
electrostatic forces. The ionized air is the conducting material, therefore, the current
starts flowing through the air gap in the form of continuous spark or arc. This arc is
produced in the arc furnaces by having air gap and electrode. With graphite or carbon
electrode the temperature obtained from the arc is between 3000oC and 3500oC.
There are two types of arc furnaces.
• Direct arc furnace.
• Indirect arc furnace.
Applications:
• In production of steel direct arc furnace is used.
• Submerged arc furnace is used for ferrous alloy manufacturer.
• Indirect arc furnace are used for melting of non ferrous metals, it is also used in
foundries where small quantities of metal is required intermittently.
gregorymasila answered the question on February 22, 2018 at 16:56
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