Different heating methodologies have historically been used for both domestic and commercial purposes. Conduction, convection and radiation are the main types of heat transfer, with more complex thermodynamics based on these three basic principles. Several heat transfer methods are implemented in manufacturing industries to change the electrical resistivity, magnetic, and physical properties of metals by using better techniques. The question is – can we use induction heaters for heat transfer too?
What is Induction Heating?
Induction heating is a process designed to heat an electrically conductive material such as a metal, to change its physical properties without the material coming into contact with the inductor. Heat is induced to the conductive material with circulating electric currents, as it is placed in a magnetic field. Metals are pre-heated to high temperatures before being pressed and hammered for example. This is known as induction forging, and an induction heater is used for heating.
Industrial processes which require manufacturers to alter metals mostly use induction heating. Metals, being good conductors, easily become soft or hard and also bond with other metals via induction heating.
For the induction heating process, the material can be placed farther away from the power supply. The material can also be immersed into liquids, gases, or kept inside a vacuum. There are no residual combustion emissions, hence metals are heated without involving any flames and smoke. The process gives an enhanced, regulated, and steady rate of heat transfer to the system with minimal heat loss.
Induction heating is useful for all those processes where you need to avoid a direct flame, achieve quick results, high quality, and durability.
Induction Heater Components
A typical induction heater consists of:
- a power supply
- an electromagnet
- an electric oscillator
- an induction work coil
The power supply source should be able to provide alternating current to the work coil.
How does an Induction Heater work?
The material to be heated is positioned inside the coil. The Induction work coil is water cooled and does not touch the heated material. The power supply is used to convert direct power to alternating current.
An electronic oscillator sends a high frequency alternating current to the electromagnet. The coil receives an alternating magnetic field. This magnetic field transfers into the material, or conductor set up for heating. An electric current, also known as an eddy current, is produced in the conductor. The conductor is then heated by the flow and circulation of eddy currents through the material resistance. This is also known as Joule heating. Ferromagnetic metals like iron can also heat up by magnetic hysteresis losses.
The initial high electric current frequency may vary depending on many factors such as the type of material to be heated, level of depth for heating, the connection type between coil and conductor, and also the size of object.
Materials for heating can be metals, semi-conductors, and also non-conductors. Glass and plastic are not conductors. To heat a material with low, or no conductivity; induction is first used to heat another conductor such as Graphite, which can transfer heat to the non-conductive material.
Induction heating is useful for many types of processes. It can be used where a very low temperature is suitable, and also for other processes where temperatures may need to be as high as 3000 degrees Celsius. Depending on the process and specifications, heating processes may take many months, or only a fraction of a second to complete.
Factors Affecting Heating Induction
The rate at which a metal will heat up depends mainly on its resistivity. If it has a higher resistivity, and low resistance, then it produces more heat as the current is passing through. But having low resistivity causes a metal to produce less heat. Therefore, ferrous metals having higher resistivity, are the most suitable for induction heating. An induction heater can also raise the temperature of Copper and Aluminium, but at a slower rate.
Heat generated in the metal also depends on the initial coil current, number of turns of the coil, frequency of power supply, coupling between the coil and material, and the electrical resistivity of the material.
If the system is connected and positioned correctly, then induction is smoother and better controlled. During and after the process, the Induction heater does not heat up.
Induction heating is used in households for cooking stoves. Industrially there are many applications of induction such as in research and design, drying objects, welding parts, shrink to fit methods, forging, melting, sealing, and also brazing.
Apart from using an induction heater, can you think of any other ways of converting electrical power into heat energy?