The location of the RTD (thermowell), positioned downstream of the orifice plate so the turbulence it generates will not create additional turbulence at the orifice plate. The American Gas Association (AGA) allows for upstream placement of the thermowell, but only if located at least three feet upstream of a flow conditioner.
A major reason for this is von K´arm´an vortex shedding caused by the gas having to flow around the width of the thermowell. The “street” of vortices shed by the thermowell will cause serious pressure fluctuations at the orifice plate unless mitigated by a flow conditioner, or by locating the thermowell downstream so that the vortices do not reach the orifice.
Also Read : Thermowell Case-Study
- Multiple Thermowell Installations Problems
- Types of Orifice Plates & Orifice Plate Tappings
- What is a Vortex flowmeter ?
- Types of Vortex Flow Meter Sensors
- Orifice Plate Turndown ratio
- Vortex Flow meter Working Animation
- Working Principle of Vortex Flow Meter
- Thermowell Wake Frequency Calculation
- Difference between Orifice & Restriction Orifice
- What is an Orifice Meter?