I have a boiling chamber that contains about 2 liters of water and a stainless steel-sheathed immersion heater with 800 W using 240 V of electricity. The heater is 7.09" (180 mm) long and looks like an elongated J shape, so the total length is about 25.6" (650 mm) long. The heaters usually are run 12 to 16 hours per day. Water is added in automatically when the water level dips 0.25" (6.35 mm).
The heaters are made so they have low watt density, but nonetheless, most of the heaters last only a few weeks. I am at a lost as to why they do not last. There are some spots on the heater, and the spots gets bigger and bigger over time. Eventually, it cracks.
Why do the heaters burn out so quickly, and how can I overcome this problem? - A.N. It is most likely that the vessel is not adequately or sufficiently agitated and total evaporation of the water is occurring on the surface of the heating elements. When this occurs, water solids will be deposited on the area where the bubble leaves the element's surface. In order to transfer heat, the temperature of the element will go up. As the process repeats itself, the element temperature will continue to rise until failure occurs. The element's surfaces must be continually washed so that scaling does not occur. An alternative would be to use demineralized water for the evaporation system makeup. - R.E. Driscoll Sr., process consultant, (817) 596-8259.