Immersion heaters are generally used when a direct heat transfer to a medium like water, chemicals or gases is required. Heat transfer is mainly through contact between the element and the medium.Depending on design the heat transfer can be enhanced by forcing the flow of the medium over the elements.

Immersion heaters are very versatile in their construction and design. Therefore their heating capacity can range from 1kW to a few MW.

Typical applications:

• Hot water tanks
• Electrically heated boilers (better control than with gas or coal burners)
• Control of bulk oil temperature in lube oil reservoirs (improves viscosity)
• For heavy weight oil (for better flow, easier pumping, increased combustion efficiency)
• Industrial water tanks, vessels and process piping
• Cleaning and rinsing tanks
• Heat transfer systems
• Circulation heating
• Steam superheating
• Heating of air or gas

Sheath material (element tube) as well as flange material must be matched to the medium to be heated. Issues with corrosion resistance, chemical stability, temperature stability, etc must be considered.

The rate of heat transfer between element and the medium is important. If heat transfer is too high, the medium might degrade. Too low a heat transfer can result in a bulky construction.

Degradation of the medium can quite often result in a precipitation of the degraded material onto the sheath. As this can reduce the rate of heat transfer, the element is put at risk of overheating.

Flow rate of the medium over the elements helps to improve the heat transfer from the element into the medium. In such a case flow velocities and equalised flow patterns are of importance.

Physical sizing of the element bundle in relation to the vessel it is mounted into, must be taken into consideration and balanced against all the other design criteria as mentioned above.

Terminal design needs to consider current/ voltage rating as well as the type of electrical protection required. Typical consideration would be a dust proof or moisture proof terminal housing (IP rating).

If the heater is used in a hazardous area, this will require substantial design considerations on the terminal layout and would require specialised certification (EX, ATEX) by third party authorities.

Mounting methods of the immersion heaters are also quite varied. Depending on sizing, the most common methods are either via screw in flange or a bolt on flange. Care must be taken that a good seal is established at the given pressure rating.