What is Thermowells?

Answer 1

Thermowells are used in industrial temperature measurement to provide isolation between a temperature sensor (often a thermocouple) and the environment whose temperature is to be measured.

They are intrusive fittings and are subject to static and dynamic fluid forces. These forces govern their design. Vortex shedding is the dominant concern as it is capable of forcing the thermowell into flow-induced resonance and consequent fatigue failure. The latter is particularly significant at high fluid velocities.

Thermowells are among the simplest yet least well publicized accessories used in industrial temperature measurement applications. There are many variations of two basic kinds; low pressure and high pressure. They are used to provide an isolation between a temperature sensor and the environment, either liquid, gas or slurry. A thermowell allows the temperature sensor to be removed and replaced without compromising either the ambient region or the process.

The most expensive, complex thermowells that we have ever seen were made from drilled molybdenum rods with an internal sheath of high purity alumina. The annular space between the alumina and metal had a very slow gas purge of nitrogen+hydrogen to prevent oxidation of the moly surface. The well was inserted into the bottom of an electrically heated glass melting furnace and used to help measure the molten glass temperature. An IR radiation thermometer mounted on an electrically insulating holder was sighted into the tube to read the temperature indicated by the alumina, essentially under blackbody conditions.

Low pressure, moderate to high temperature environments are routinely provided with a thermowell variant called a protection tube that can be made of metal or high temperature glass or ceramic, again according to he conditions. Most high temperature industrial furnaces use ceramic or metal protection tubes, according tho the conditions.

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