Knowing your flow measurement data can be critical to ensuring your business is profitable. Accurate flow measurement improves efficiency, reduces costs, helps ensure regulation compliance, and gives you data to make sure you’re not wasting any precious liquid or gas. Poor measurement is expensive!
Proper flow measurements come from a properly selected flow meter coupled with a quality, proven flow conditioner and well designed piping layout.
The Formula
Differential flow meters report based on velocity, temperature, pressure, viscosity. Fluid flow rate can be expressed by the simplified expression:
Fluid flow through pipe = average velocity x cross sectional area of the pipe. (Q = V x A)
Orifice Meters
The device that’s often forgotten in discussions but is one of the most popular devices in service for fluid measurement. Orifice meters are very dependable with an extremely significant amount of testing, but are also very sensitive to their construction and quality. The construction of pipe taps, orifice plate quality, and meter tube surface roughness are all significant factors in meter accuracy. When meter tubes are not correctly inspected or don’t comply with measurement standards, significant measurement errors can easily be missed. And those errors cost you money.
To help mitigate this risk, make sure your orifice fitting meets manufacturing requirements, and that your meter run complies with AGA/API requirements.
Flow Nozzle
The flow nozzle is an extremely simple form of dP measurement design that often comes as one single part. Pressure measurements are taken from the taps on the meter run piping, or from the nozzle body itself. They have no moving parts and are very robust, and often used in more unusual or extreme measurement applications with more complex fluids.
CPA’s flow nozzles are customized to your specific project and flow type (liquid, gas, or even steam). All of CPA’s nozzles are designed using ISO 5167, ASME 3M, or ASME PTC-6 and will be based on your desired DP, throat size, and process conditions.
Flow nozzles are for subsonic flows only. In critical choked flow conditions, a sonic nozzle is used instead!
Venturis
A venturi nozzle helps give a lower pressure drop versus the basic flow nozzle. The addition of an outlet diffuser helps increase the recovery in the pressure drop.
The Venturi is a differential pressure measurement device that has an inlet radius, a cylindrical throat, and an expanding outlet cone. Pressure taps can be included in the nozzle body, in the pipe flanges, or in the pipe itself.
Our venturis are all custom designed based on your desired application and measurement standard. They are suitable for all fluid applications, and many different installation methods can be done. The most typical installation is for ANSI Raised Face flanges, but other flange styles like RTJs can be done as well.
For more severe applications where flanges aren’t being used, CPA can easily design with butt weld connections in mind so that there is zero risk of a flange/gasket leak.
Sonic Nozzle
Sonic nozzles are physically very similar to a flow nozzle or venturi, their big difference is the design standard and applications being used. The nozzle is designed to protect your flow meter or other sensitive equipment from being damaged by excessive velocities in gas applications. They are designed to work alongside the flow meter’s max flow rate, where any excessive velocity results in the nozzle choking.
If you have a choked flow condition as stated above, the sonic nozzle will protect your gas meter or other pipe equipment from damage. They are consistent with limiting flow by just the exact calculated amount, and can be sized to protect all kinds of equipment, including your orifice meter.
Sonic Nozzles create a restriction within the pipe, and at a certain velocity (their designed choking point), they form a shockwave within a nozzle throat that prevents the flow rate from increasing further. They are then installed downstream of the critical equipment, so that any downstream drops in pipe pressure will not reach the meter or velocity sensitive device.
When it comes to sonic/restriction applications, sonic nozzles are far superior to restriction orifice plates. While an orifice place does not properly choke (meaning the mass flow rate continues to increase while downstream suction is reduced), the sonic nozzle maintains a constant mass flow rate.
Additionally, sonic nozzles can be used when you need to extend the range of a pressure control valve or volumetric flow meter. Because the sonic nozzle creates a downstream pressure drop, it can increase the pressure in the meter tube—moving more fluid and extending the operating range.
Sonic nozzles are usually installed between two raised face flanges, with a portion inserted into the pipe. Like the flow nozzle, sonic nozzles have no moving parts or maintenance, and come in many customizable variations.
Barriers to Accurate Measurement
No matter what flow measurement device you go with, they all need the same basic requirements to maintain consistent and accurate results. They are:
- Fully developed flow profile
- Swirl free flow
- Consistent, repeatable behavior
Enhancing flow and measurement accuracy means considering all elements of your pipeline, and designing solutions specifically customized to your needs. A crucial element to achieving accuracy requirements is the use of a flow conditioner. That’s because flow conditioners provide flow profile recovery and swirl elimination, leading to repeatable behavior. Simply put, flow conditioners make your meter’s performance requirements far more attainable.
Ongoing research has shown that CPA plate style flow conditioners consistently outperform tube bundles when it comes to measurement performance and meter repeatability. They also have considerably lower pressure drop, sometimes 10-100 times better than that of a tube bundle!
As per all our products, the flow conditioner you need is customized and manufactured to your project’s specifications. No matter your fluid, flow conditioners help deliver accurate measurements, every single time.
Partnering with You
Our engineers at CPA work with you to evaluate and recommend the right products for your specific project. We can help you determine not only the best conditioner and meter, but also the materials used, length and width required, and more. We are partners in your success and, better still, our phones are answered by humans instead of robots! Give us a call today to discuss your needs and we’ll be happy to help you achieve consistent, reliable results that positively impact your bottom line.
