The basic principle on which an immersion heater works is Joule heating. It states that an electric current passing through a resistor will convert that electrical energy into heat energy. The basic component of an electric immersion heater is its heating elements which consists of a resistive wire, a layer of electric insulator coated over it, and a protective metallic outer sheath. The wire made of a resistive alloy such as Nichrome heats up when an electric current is applied to it. The insulator layer, usually made of compounds such as Magnesium Oxide (MgO), transfers the heat to the outer metallic layer and finally the outer layer, generally made of steel or stainless steel, dissipates the heat to the medium to be heated.
Immersion heaters are heaters which can be immersed in a liquid and then heat the liquid inside the tank or container uniformly. Types of Electrical Immersion Heaters commonly used are as follows:
1. Over-the-Side Immersion Heaters
These types of immersion heaters are commonly used in places where through-the-wall heaters cannot be installed and in tanks where the heater can be removed without emptying the contents of the tank. These heaters are generally placed along the side wall of the tank and the heating element is either at the bottom or the side of the tank.
2. Flanged Immersion Heaters
A flanged immersion heater consists of “U” shaped tubular heating elements welded or brazed to a round or square flange. These types of immersion heaters are used in large vessels or applications involving high pressure. The flanges of such heaters have bolts which are screwed to the base flange present inside the tank.
3. Threaded or Screw Plug Immersion Heaters
This kind of immersion heaters consists of a hairpin bent tubular heating element welded to an NPT fitting. Their NPT base enables them to directly screw or plug into the wall of the tank through a threaded opening. These heaters are ideal for applications requiring process water heating and freeze protection.
Immersion heaters are very cost effective as their design is simple, build is robust, and very efficient as they are in direct contact with the medium to be heated. Immersion heaters have a wide range of industrial as well as domestic applications and several manufacturers provide high-quality customized immersion heaters and heating elements for such purposes.