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SONIC NOZZLES:
For Accurate Flow Measurement and Control of Gases
Sonic Flow Primary Elements
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The SONIC NOZZLE, also known as a "Critical Flow Venturi" or "Critical Flow Nozzle"
is accepted
internationally as a flow measurement standard
and flowmeter.
Originally used by the aerospace
industry, Sonic Nozzles are now utilized for
many diverse applications in the automotive,
energy and metrology industries.
Sonic Nozzles can be used as a
calibration standard for gas flowmeters or any
flow measurement device.
By design, Sonic Nozzles are a constant
volumetric flowmeter. However,
with the use of a regulated pressure supply,
the Sonic
Nozzle becomes a “state-of-the-art” mass
flowmeter.
More
information about Sonic Nozzle Technology is
contained in the following technical paper,
"What
is the Best Transfer Stander for Gas Flow?"
by John D. Wright, NIST-National Institute
of Standards and Technology. |
FLOW SYSTEMS designs and manufactures Sonic Nozzles in accordance with both ASME and ISO standards. The geometry is such that the gas is accelerated along the circular arc converging section and then is expanded in a conical diverging section, which is designed for pressure recovery. In the throat, or minimum area point of the Sonic Nozzle, the gas velocity becomes equal to the speed of sound. At this point, gas velocity and density are maximized, and the mass flow rate is a function of the inlet pressure, inlet temperature, and the type of
gas.
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Figure 1 ASME / ISO Torodial Throat Critical Flow Venturi
Note 1: +/-0.000" -0.001" for
0.016" <=d <=0.707", +/-0.001 for d
> 0.707"
Considering both the divergent section design and the flow rate, Sonic Nozzles may operate with an exit pressure as high as 90% of the inlet pressure. If more information is desired, FLOW SYSTEMS has published numerous technical papers on the subject of Sonic Nozzle theory.
A complete metering system includes a Sonic Nozzle, Inlet
and Exit Sections, Pressure and Temperature Sensors,
and a Flow
Computer.
Click here for a
Primer on Critical
Flow.
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The advantages of a Sonic Nozzle-based metering system are numerous:
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ADVANTAGES
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Internationally Recognized
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Mass Flow Varies Linearly with Inlet
Pressure
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Minimal Upstream Piping Required
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Long Term Accuracy
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Excellent Repeatability
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No Moving Parts
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Differential Pressure Measurement Not
Required
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Flow Rate Is Not Affected by Downstream Flow
Disturbances
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Mass Flow is Constant with Varying Downstream
Pressure |
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APPLICATIONS
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Calibration of Gas Flow Meters
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Gas Flow Metering
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Calibration of Turbine Engine Component Gas
Passages
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Calibration of Automotive Component Air
Passages
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Measurement of Automotive Induction
Air
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Automotive Emissions Testing
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Compressor Discharge Capacity
Tests
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Valve CV Tests
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Flow Limiting
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Over Speed Protection of Gas Flow
Meters |
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Application notes are available from FLOW SYSTEMS that discuss in detail, many success stories with Sonic Nozzles.
Application engineering services are offered to assist you with any questions.
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DESIGN OPTIONS
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Sizing - FLOW SYSTEMS will size Sonic Nozzles to meet the requirements of each application. Throat diameters are offered from
0.016 inches and larger. Throat diameter tolerances
are: +/-0.000" -0.001" for 0.016"
<=d <=0.707", +/-0.001 for d >
0.707".
To date, the largest Sonic
Nozzle we have produced had a throat diameter of 14.6 inches.
Certain standard sizes are available for immediate shipment with or without calibration. For assistance with sizing, contact the Sales
Department or refer to the FLOW SYSTEMS
Charts that show estimated mass flow performance for standard sizes of Sonic Nozzles.
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Line Size - Line sizes vary from
dia. 1/4 in. tubing to the largest pipes or ducts.
End Connections
- Sonic Nozzles can be configured with almost any desired
connection such as "AN" flare, NPT, ANSI Flange,
Swagelok, VCO, VCR, CPV, butt-weld or weld-in. Custom flanges with O-Ring seals (with or without V-Clamps) are also available upon request. Insert type meters are designed to be held between flanges and
are available at a lower cost.
Material of Construction - Generally 300-Series stainless steel is recommended, however other materials such as aluminum, carbon steel and machinable plastics may be used. |
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Diffuser Options - The divergent section of FLOW SYSTEMS' Sonic Nozzles are designed for maximum pressure recovery and economy. Our standard diffuser geometry is 7 throat diameters in length with a 4-degree half angle for throat diameters greater than 0.044 inches. A 10 throat diameter, 3-degree half
angle diffuser is used for nozzles with throat diameters ranging from 0.022 to 0.044 inches. Small nozzles, throat diameters ranging from
0.016 to 0.044 inches. Custom
geometry may specified by the end user.
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Meter Tubes - INLET and EXIT SECTIONS are available to provide users with a complete meter run. Inlet Sections, designed to meet the proper upstream straight piping requirements, also contain taps for pressure and temperature measurements. Multiple or additional taps, pressure-averaging piezometer rings, and flow conditioners are also offered. Standard Inlet and Exit Sections, in stock for immediate shipment, are compatible with FLOW SYSTEMS' standard Sonic Nozzles.
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30"
Diameter Flange with 21 - 1" Sonic Nozzles
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MULTIPLE
SONIC NOZZLE ARRAYS
FLOW SYSTEMS specializes in designing arrays of Sonic Nozzles that share a common inlet plenum. These arrays allow for increased rangeability in flow rate and offer compactness in design.
Manifold Size Selection and Number of Elements Allow Rangeability
See FLOW SYSTEMS' Drawings 125009,
1259010, and 1259011
for more details on Multiple Nozzle Arrays.
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ACCURACY
Without calibration, ASME predictions for flow rate accuracy, assuming the use of reasonably accurate instrumentation, are at best +/-
1.0% of reading. Flow calibrations traceable to NIST in conjunction with standard instrumentation packages allow for: +/-0.65%, +/-
0.54%, 0.27% and 0.14% of reading accuracy levels. A technical note is available from FLOW SYSTEMS that contains a more thorough discussion of gas flow measurement
accuracy using Sonic
Nozzles.
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FLOW COMPUTERS / INSTRUMENTATION
Flow
Computer - Model FC175-CFV
Shown with
interchangeable Sonic Nozzle Meter Run
and Customer-Supplied Laptop Computer.
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FC175
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FEATURES
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Use with single, manually interchangeable Sonic
Nozzles or Sub-Sonic Venturis.
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MS-Windows™-based Setup Software and Interface
allow Easy Configuration and Monitoring
Capabilities.
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USB Communication.
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Optional External Pressure Sensors or simply connect
an existing Absolute / Differential, 2-wire,
Loop-Powered, 4-20ma output transmitters.
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Includes a 2252 kΩ Thermister Probe for
temperature measurement.
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Custom Software and additional, User-Scaleable, I/O
channels available.
(3) Thermister (1-2) scaleable 4-20 MA DC.
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PC Connection Required.
(No Stand-alone Operation.)
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Self-contained Package, including Instrumentation.
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Calibration Software to Maintain Internal
Instruments.
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Test Set-up Screen.
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Flowmeter Configuration.
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Data Logging Capabilities via USB Interface.
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Optional Internet Support and Diagnostics.
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Calculations per ASME MFC-7M / ISO 9300.
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Real Gas Properties for most gasses.
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Iterative Solution for Cd-based on Actual
Calibration Data or Theoretical Models.
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Best Economy.
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FC175 Flow Computer
Dimensions:
6.5 in. W x
2.1 in. H x 6.5in. D
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Below is a summary of instrumentation configurations and
accuracies for the FC175.
Options include a humidity sensor for moist air applications, required fittings, lead wire and tubing.
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Options
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Configuration
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Mass Flow Accuracy
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Comments
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-01,
-01A
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Level 1
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+/-0.95% of Reading
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Assumes: +/-0.5%
CEESI calibration,
4:1 pressure range
(+/-0.2% full scale) & 40° to 100°F gas
temperature (+/-0.2°C).
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Level
2
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+/-0.65% of Reading
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Assumes: +/-0.5%
CEESI calibration,
4:1 pressure range
(+/-0.1% full scale) & 40° to 100°F gas
temperature (+/-0.2°C).
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Level 3
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+/-0.54% of Reading
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Assumes: +/-0.5%
CEESI calibration,
4:1 pressure range
(+/-0.05% full scale) & 40° to 100°F gas
temperature (+/-0.2°C).
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Level 4
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+/-0.27% of Reading
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Assumes:
+/-0.25%
CEESI calibration,
4:1 pressure range
(+/-0.02% full scale) & 40° to 100°F gas
temperature (+/-0.2°C).
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FC500
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| FEATURES
» For use with single Sonic Nozzles,
Venturis, or Multiple Sonic Nozzle Arrays.
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Advanced Functionality for the High-End User.
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Self-Contained Package including Instrumentation.
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MS Windows™-based Configuration and Monitoring Software.
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Ethernet, Analog (2), and Configurable Relay (2) Outputs.
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Stand-Alone Operation with Internal or Remote Data Logging Capabilities.
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Calculations per ASME MFC-7M / ISO 9300.
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Combines the Performance of a Control Valve and a
Flowmeter in One Package.
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Real Gas Properties for most gasses.
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Iterative Solution for Cd-based on Actual Calibration Data or Theoretical Models.
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Rack-mount or Bench-Top.
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Internet Support and Diagnostics.
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Calibration Software to Maintain Internal Instruments.
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FLOW SYSTEMS' FC500 Flow Computer
Shown with Optional Sonic Nozzle Array. |
Below is a summary of instrumentation configurations and
accuracies for the FC500.
Options include a humidity sensor for moist air applications, required fittings, lead wire and tubing.
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Mass Flow Accuracy
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Comments
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| Level 1
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+/-6.45% of Reading
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Assumes:
diameter 0.031" uncalibrated nozzle, 6:1 pressure range
(+/-0.1% full scale) & 40° to 100°F gas temperature.
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| Level 1
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+/-0.88% of Reading
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Assumes:
diameter 0.500" uncalibrated nozzle, 6:1 pressure range
(+/-0.1% full scale) & 40° to 100°F gas temperature.
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| Level 2
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+/-0.56% of Reading
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Assumes:
+/-0.50%
CEESI calibration, 6:1 pressure range
(+/-0.04% full scale) & 40° to 100°F gas temperature.
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| Level 3
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+/-0.29% of Reading
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Assumes: +/-0.25% CEESI calibration, 6:1 pressure range
(+/-0.02% full scale) & 40° to 100°F gas temperature.
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| Level 4
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+/-0.14% of Reading
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Assumes:
+/-0.10% CEESI calibration, 6:1 pressure range
(+/-0.01% full scale) & 40° to 100°F gas temperature.
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FLOW CALCULATION
SOFTWARE/EQUATION REPORT
For users with existing instrumentation, FLOW SYSTEMS offers software to calculate
the flow rate through Sonic Nozzles. The available format is Microsoft
Excel™. An equation report will allow users to program the flow equations directly into existing
software / data acquisition systems.
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SYSTEMS
FLOW SYSTEMS combines Sonic Nozzles with instrumentation, data acquisition, controls, computational products, prime movers, and material handling to provide our customers with
fully automated, turnkey systems. Systems may be used for gas flow measurement, calibration of other flowmeters, or product performance testing. Users may select a standard system or a custom system that can be designed
to meet exacting specifications. Systems are programmed with National Instruments LabVIEW™ software. Our Consulting Services can even help clients prepare their system specifications. Contact the sales department for more information on our System Integration Services.
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CHOKING PRESSURE RATIO (CPR) TESTING
FLOW SYSTEMS
provides a CPR value with all standard-size Sonic Nozzles in most fittings. The CPR will be determined on our automated test stand. This will give users a more defined operational range for each Sonic
Nozzle.
Swagelok®,
VCO® and VCR® are registered trademarks of Cajon Company, Macedonia, OH.
CPV® is a registered trademark of CPV Manufacturing Inc., Philadelphia, PA.
Excel® and Visual Basic® are registered trademarks of Microsoft Corporation, Seattle, WA.
3095MV® is a registered trademark of Fisher-Rosemount, Eden Prairie, MN.
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