Over-the-side heaters are immersion heaters that hang over the side of a tank to heat the tank itself, or the materials within. Over-the-side heaters are used in situations where heaters cannot be installed, portability is required, or where heaters must be removed for cleaning without emptying the tank. In addition to heating materials in a tank, over-the-side heaters may be used prevent freezing or to heat viscous materials to induce and improve flow. Over-the-side heaters consist of a heating element surrounded by a protective sheath or sleeve. Selecting the proper sleeve material is important since the sleeve is the portion of the over-the-side heater that comes in contact with the process media. Care must be taken to ensure that the sleeve material does not react, corrode, rust, or breakdown in the presence of the media. Some styles of over-the-side heaters are designed with changeable sheathes so that they can be used with different media types.
Over-the-side heaters differ in terms of sleeve materials and applications. Choices for sleeve or sheath materials include aluminum, brass, copper, fluropolymer, high temperature foil (HT foil), iron, nickel alloy, polyimide, natural or synthetic rubber, steel or stainless steel. Applications for over-the-side 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. Over-the-side heaters that are used with corrosive and caustic solution are sheathed typically in stainless steel, polymers, or high-strength alloys.
Power requirements for over-the-side heaters include maximum operating (sheath) temperature, phase, required AC 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. Some over-the-side heaters use single-phase power. Others use three-phase power. Heating capacity is the wattage which an over-the-side heater can deliver. Watt density is a good measure of how quickly the heater can transfer heat to a heated surface. To calculate watt density, suppliers divide the available wattage by the heated surface area. Insertion length or heated length is also an important parameter to consider when selecting over-the-side heaters.
Over-the-side heaters are available in different shapes for different applications. The most common shapes are “L”, “O”, vertical loop, and tube. L-configuration heaters are shaped like the letter “L”. O-heaters are circular or donut-shaped. Vertical loop over-the-side heaters have a vertical configuration, while tubular heaters consist of a single tubular element. Features for over-the-side heaters are also an important consideration. Choices include: corrosion resistant, cryogenic use, dynamic power regulation, explosion-proof, encased coil, finned, grounding wire, internal temperature detector, microprocessor controlled, overheat protection, portable, thermostat, UL approved, and weatherproof housing. Hazardous location heaters are designed for use in places where there is a risk of fire or explosion. Underwriters Laboratories (UL) and other organizations rate these devices. Indirect fired heaters use a secondary heat exchanger to separate the breathable air stream from the combustion air stream.
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