Immersion heaters are the answer for situations in which fast, efficient heat transfer is required. These heaters are used by the process heating industry for a wide range of applications.
A common type of immersion heater is the screw-plug immersion heater, utilized inside of tanks. The tubular heating element of the heater is inserted into a threaded opening on the side of the tank near the bottom, and then the brass, steel or stainless steel screw plug end of the heater is secured into place. Applications include hot water tanks for domestic use.
Another basic immersion heater is the flanged immersion heater. Instead of a screw plug end, the tubular heater is welded or brazed into a round or square carbon steel pipe flange. The heater is then fitted into a pipe body, tank or pressure vessel.
Both kinds of immersion heaters are extremely efficient and economical because their energy is generated from within the substance that needs to be heated. Screw-plug configurations include only a few heating elements; however, flanged configurations can hold bundles of heating elements for larger wattage requirements.
All immersion heaters consist of two major parts: the tubular heating element(s) that is immersed in the liquid or gaseous substance to be heated and the electrical terminal that remains outside of the liquid or gas. The electrical unit extends from the screw-plug or the flange end of the heater and is protected by a NEMA enclosure. NEMA 1 enclosures are for general purpose applications; NEMA 4 enclosures are moisture resistant for exposed-to-the-elements conditions; and NEMA 7 enclosures are explosion resistant and are used in hazardous locations. The enclosures could also include a thermostat control, and thermowells are utilized on the heating element end of the heater to protect the temperature sensor.
Depending on the corrosive level the heating elements will encounter, several different sheath materials are available for covering and protection. Some common materials used for this purpose include titanium, Incoloy, Inconel, steel, stainless steel and copper, each with its own ideal applications.
Copper is used for potable water; steel is good for hydraulic oils; stainless steel is ideal for mild acids; and Incoloy is great for alkaline solutions and high temperature air and gases. Immersion heaters come in a variety of shapes, sizes and configurations. Important considerations when choosing an immersion heater include the best screw-plug or flange size for the application, available length space for the heating elements, the appropriate watt density, the necessary electrical terminal and the proper sheath for the solution being heated.