Immersion Heaters

Immersion heaters are used in applications that require the heater to be immersed in the substance to be heated. They are equipped with pipe threads, flanges or other mounting hardware. Flange immersion heaters are equipped with a flange that is installed by bolting the heater to a matching flange that is welded to the vessel wall. Screw plug immersion heaters are equipped with a pipe fitting which screws into a threaded well. With both types of heaters, caution must be taken in evaluating the desired heat transfer rate to the heated substance. High-watt density immersion heaters should not be used with extremely viscous materials, explosives, or substances that are not well circulated because the risk of fire or scorching increases as fluid viscosity and heater-watt density increase. Common applications for flange and screw plug immersion heaters include the heating of gases or vapors, clean water, process waters, high-purity waters, lightweight oils and degreasing solutions, heavy weight oils, medium weight oils, mild corrosive solutions, severe corrosive solutions, caustic solutions, and liquid paraffin.   

Flange and screw plug immersion heaters can use AC or DC voltage and single-phase or three-phase power. Most heaters used alternating current (AC) instead of direct current (DC). Power requirements to consider include maximum operating (sheath) temperature, required voltage, heating capacity, and watt density. Maximum operating (sheath) temperature is the highest temperature that the heater's sheath (or protective cover) may reach. This is not the maximum temperature a heated substance may reach. Measured in kilowatts (kW), heating capacity is the wattage that a flange immersion heater or screw plug immersion heater can deliver. Watt density is a good measure of how quickly flange and screw plug immersion heaters can transfer heat to a heated surface. To calculate watt density, suppliers divide the available wattage by the heated surface area.  

Most flange and screw plug immersion heaters have a protective sheath or sleeve that covers the heating elements. There are usually many choices for sheath or sleeve material. Examples include aluminum, brass, copper, fluropolymer, high temperature (HT) foil, iron, nickel alloy, polyimide, rubber, steel, stainless steel, and synthetic rubber. Aluminum provides good electrical and thermal conductivity, high reflectivity, and resistance to oxidation. Brass is a copper-based alloy that offers good strength, excellent high temperature ductility, reasonable cold ductility, good electrical conductivity, excellent corrosion resistance, and low magnetic permeability. Copper is one of the best conductors of heat and electricity. Fluropolymers such as Teflon ^® (DuPont Dow Elastomers) are highly-resistant to temperature, chemical reaction, corrosion, and stress-cracking. HT foil is usually made of ceramic materials (ceramic foil). Stainless steel is a chemical and corrosion resistant alloy that can have relatively high-pressure ratings. Flange and screw plug immersion heaters may also use synthetic rubber such as neoprene for the sheath or sleeve material.

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Part Numbers for Immersion Heaters