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What are the different types of Electric Heating?
Electric Heating
The process in which electrical energy is converted into heat by resisting the free flow of electric current is known as electric heating. Therefore, the heat is produced due to circulation of electric current through a resistance. This electric current may be circulating directly due to the application of potential difference or it may be due to induced eddy currents.
Different Methods of Electric Heating
The classification of methods used for electric heating is shown in the figure.
Direct Resistance Heating
In this method of electric heating, the electric current is passed through the substance to be heated. This method of electric heating is mainly used in electrode boiler for heating water and resistance welding.
Indirect Resistance Heating
In this method of electric heating, the electric current is passed through a high resistance heating element. The heat produced in the element is given by Joule’s law (i.e., I2Rt). Then, the produced heat is delivered to the substance to be heated either by radiation or convection or by combination of the two. This method of electric heating is mainly used in immersion water heaters, resistance ovens, domestic cooking, heat treatment of metals, etc.
Infrared or Radiant Heating
In infrared or radiant heating, the heat energy is transferred from source to the body to be heated in the form of electromagnetic radiation. Generally, this method of electric heating is used for drying clothes in textile industry and to the dry the wet paints on the objects.
Arc Heating
The electric arc drawn between two electrodes develops very high temperature, about 3000 °C to 3500 °C depending upon the material of the electrode. This generated heat energy may be used in various heating processes.
Direct Arc Heating
In this method of electric heating, the arc is produced by striking the electrode to the body to be heated and the heat so developed is directly conducted and taken by the object. The main application of this type of electric heating is in the production of steel.
Indirect Arc Heating
In indirect arc heating, the arc is established between the two electrodes, the heat so developed is transferred to the substance by radiation. This method of electric heating is generally used in the melting of non-ferrous metals.
Direct Induction Heating
In direct induction heating, the electric current is induced by electromagnetic action in the body to be heated. The induced current when opposed by the resistance of the body develop the heat and hence raise the temperature. Direct induction heating used to melt the object in induction furnace, also the eddy current heaters are used for heat treatment of metals.
Indirect Induction Heating
In this method of electric heating, the eddy currents are induced in the heating element by electromagnetic induction. These eddy currents in the heating element produce the heat which is transferred to the body to be heated up by radiation and convection. Indirect induction heating is used in certain ovens used for heat treatment of metals.
Dielectric Heating
Dielectric heating is used for heating insulators such as wood, plastic, etc. which cannot be easily heated by other electric heating methods. Dielectric heating is also called the high-frequency capacitive heating. The supply frequency required for dielectric heating ranges from 5 MHz to 5 GHz and the applied voltage is about 20 kV.
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