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Wake Frequency

June 13, 2014
H&B One Piece Thermowell

The purpose of a thermowell is to allow removal of the temperature sensing element without disrupting the process.  With the temperature sensing element installed however, it is important that process temperature is transferred through the thermowell efficiently and with minimal effect on response time.


Thermowell Wake Frequency calculations are generally conducted prior to thermowell manufacture.  They ensure that the thermowell design is robust enough to cope with varying stresses and strains produced by the process media.  Fluidic are able to provide Wake Frequency Calculations where the following process data is available:


  1. Pressure
  2. Temperature
  3. Velocity (or flowrate with linesize)
  4. Viscosity
  5. Density


Any thermowell failure will occur at the highest stress point, ie between the flange/shaft join.  With the exception of the use of velocity collars (which cause their own problems, and are not recommended within current ASME PTC 19.3 TW-2010 standards), this has traditionally meant shortening of, or bulking up the thickness of, the thermowell.  Both of these techniques will significantly increase response time and are detrimental to temperature measurement performance.


In applications where the Thermowell Wake frequency calculation fails due to Strouhal frequency (such as in the example calculation shown below) Fluidic’s partner, Okazaki, have developed the VortexWell thermowell.  This helical design sheds vortexes normally caused by the thermowell itself and therefore cancels out the resonance failure issue apparent in traditional thermowell design.  Using an Okazaki Vortexwell in the example shown would therefore be deemed a technically sound install for this application.


 Download   Sample Thermowell Wake Frequency Calculation


For more information on wireless instrumentation, please call your local Fluidic office. To receive more technical application notes like this please click the subscribe link below.


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