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Thermowells are recommended
whenever a temperature element is to be inserted into a process where
corrosion, pressure, abrasion, or shear forces may threaten the life of the
element. In addition thermowells allow for a defective instrument to be
removed without shutting down or draining the process. 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.
Low Pressure
Fabricated
Pockets are precision components manufactured to the highest standard from
pipe, tube and bar, to serve as protective devices for primary sensing
elements of all types.
High Pressure
Solid Drilled Thermowells are precision components manufactured to the
highest standard from bar or forgings, to serve as protective devices for
primary sensing elements of all types. A wide range of possible products are
available. Conditions of pressure, temperature and corrosion resistance
govern the size, shape and selection of materials to ensure optimum
dependability system response and accuracy.
Wake
Frequency Problems
When fluid flows past a thermowell inserted into a
pipe or duct, vortices form at both sides of the well. These vorticies
detach, first from one side, and then from the other. This phenomenon is
known as the Von Karmann effect. The frequency of shedding of these vortices
is a function of the diameter of the thermowell, the fluid velocity and, to
a lesser extent, the Reynolds number. The vortex shedding subjects the
thermowell to a periodic transverse force. As the vortex shedding frequency
approaches the natural frequency of the thermowell, the thermowell will
oscillate, and is liable to snap off. (The natural frequency of the
thermowell is a function of its shape and material of manufacture.) The Von
Karmann effect must be taken into account when designing thermowells of
sufficient strength to withstand service conditions, and generally
thermowells are chosen such that the shedding frequency is always less than
or equal to 80% of the natural frequency.
Corrosion
Factors
Material chosen for
Thermowells is governed by the corrosion conditions the well will face.
View Corrosion Chart
Thermowell Material is an
important factor when considering the thermowell design.
View
Thermowell Materials
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