What is Wake Frequency Calculation?
26 January 2025
Wake frequency calculations prove the suitability and required dimensions of thermowells and insertion flowmeters based on the process conditions and provide maximum safety for plant operation.
Thermowell wake frequency, is a physical characteristic resulting from the interaction of a thermowell with the fluid flowing past it. The thermowell dimensions and geometry, the properties and process conditions of the fluid flowing past the thermowell all determine the effects and frequency of the wake vortices.
Wake Frequency Calculations have many applications, including:
· Chemical & Petrochemical Industries
· Onshore & Offshore refineries
· Natural gas pipelines
· Heat Recovery Steam Generators (HRSG)
A wake frequency calculator takes four types of stresses into account. Each type of stress, if unchecked, could cause the thermowell to fail. Therefore, the thermowell or insertion flowmeter must pass in all four areas to be acceptable for use in your application:
Frequency Stress
First, the resonance frequency of the thermowell must be high enough so that the process fluid flow won’t trigger damaging vibrations.
Static Stress
Next, hydrostatic fluid pressure and non-oscillating drag forces create static stresses. The steady-state stress should not exceed what the thermowell can support.
Dynamic Stress
Furthermore, dynamic or oscillating stresses arise from drag and lift forces. This stress must be less than the fatigue stress limit for the thermowell.
Hydrostatic Pressure
Additionally, external pressure must not exceed the pressure the thermowell can handle at its operating temperature. This applies to the tip, shank, and flange or threads.
The Wake Frequency Calculation data is available with the following basic parameters:
Velocity
The velocity of your process liquid impacts forces such as lift and drag that act on the thermowell.
Density
Moreover, density, which can be mass per volume or specific gravity, combines with velocity to affect the forces on the thermowell.
Max Operating Pressure
The operating pressure and temperature of your media, in turn, impact the thermowell’s stress level.
Viscosity
Viscosity, or the thickness of your process media, measures its resistance to shear stress.
Temperature
Extreme temperatures, along with high pressure, create an even more demanding environment.
Thermowell Dimensions
Lastly, the thermowell’s dimensions influence the wake frequency calculation.
