Electric Immersion heaters may heat water immediately adjacent to the heating element high enough to promote the formation of scale, commonly calcium carbonate, in hard water areas. This accumulates on the element, and over time, as the element expands and contracts through its heating cycle, the scale cracks off and drops to the bottom of the tank, progressively filling up the tank. This reduces the tank's capacity and, where the immersion heater is secondary to the heating of the water by a coil fed from a gas or oil-fired boiler, can reduce the efficiency of the primary heating source by covering that other coil and in turn reducing its efficiency. Regular flushing-out of accumulated sediment can reduce this problem.Such problems can be avoided at the design stage, by maximising the amount of hot element in the liquid, thus reducing the watts density. This reduces the working temperature of the surface of the element, reducing the build up of limescale. So watt density has to be revised as per application.
Prevent excessive temperatures in process applications.
A reliable temperature control system is imperative to the performance and life of your heaters.The temperature sensing device should be located in a built-in thermo well for maximum accuracy and responsiveness.The protection of a high-temperature limit control can be very important, especially when process temperatures are critical.
Guard against heater contamination.
Contamination is the most frequent cause of heater failure. Any organic or conductive material if allowed to collect at the lead end of the heater, contaminants can cause an electrical short between the power pins.Do not allow lubricants, oils, low-temperature tapes or processing materials to remain in contact with the lead end of the heater. Specify a moisture seal if necessary.
Protect leads from damage by high temperatures.
Standard fibreglass-insulated lead wire may be used to approximately 500ºF (260ºC) ambient. If the lead will be exposed to higher temperatures, high-temperature lead wire or ceramic bead insulation should be used. Ground the equipment. An unheated section of the heater, protruding from the heated part, could enable the leads to run cooler.
Protect leads from damage by excessive movement.
Anchor the leads to prevent heaters from being damaged when they are mounted in moving machinery.
Prevent excessive cycling.
Excessive cycling can be very detrimental to the life of a heater. The worst cycle rate is one which allows full expansion and full contraction of the heater at a high frequency (approximately 30 to 60 seconds ON and OFF).With simple ON/Off controls, much less frequent cycling can be achieved by closely matching the total wattage to the actual requirements.
For immersion applications of heaters
Make sure the sheath material and watt density ratings are compatible with the liquid being heated. Do not locate the heater in a restricted space where free boiling or a steam trap could occur.Immersion heaters used in tanks should be mounted horizontally near the tank bottom to maximize convective circulation.Vertical mounting is possible where limitations prohibit horizontal orientation. Both methods must be located high enough to be above any sludge build-up in the bottom of the tank.Scale build-up on the sheath and sludge on the bottom of the tank must be minimized.
Heater selection and sizing are important.
Match the heater wattage as closely as possible to the actual load requirements to limit ON/OFF cycling.For fitted-part applications, specify the heater size exactly so it can be tightly fitted. Even small air gaps cause hot spotting.Its common sense and a safe practice to electrically ground all equipment which protects plant and personnel in case of any electrical failure in the heating system.
Ground the equipment.
It's common sense and a safe practice to electrically ground all equipment on which the heater is used. Grounding protects plant and personnel in case of any electrical failure in the heating system.