Watt Density & Sheath Material

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The two most critical factors that affect the durability of a tubular heater are:

■ Sheath material

■ Watt density

The sheath material type of a tubular heater depends on the operating temperature and the corrosivity of the medium within which the heater will operate. The watt density distribution on the surface of a tubular heater is critical for two reasons. First it determines the temperature that a heating element sheath will attain within the conditions that the heater is subjected to. The second reason is that every material has a specific maximum watt density that it can tolerate during its heating cycle. Table 1 below lists various sheath materials, maximum allowable temperatures and mediums within which they are recommended to operate. Table 2 lists recommended maximum watt densities and maximum operating temperatures for different materials. Graphs 1, 2, 3 and 4 show the relationship between the sheath temperature of a tubular heater and its watt density in different conditions.

Maximum Watt Density Ratings for Various Solutions