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eLibrary >
ASHRAE Standard 41.8-2023 -- Standard Methods for Liquid Flow Measurement (ANSI Approved) >
ASHRAE Standard 41.8-2023 -- Standard Methods for Liquid Flow Measurement (ANSI Approved), 2023
- ASHRAE Online Bookstore
- Addenda
- Errata
- Return to Previous Page
- ANSI/ASHRAE Standard 41.8-2023 [Go to Page]
- Contents
- Foreword
- 1. Purpose
- 2. Scope
- 3. Definitions
- 4. Classifications [Go to Page]
- 4.1 Liquid Flow Measurement Applications. Liquid flow measurement applications that are within the scope of this standard shall be classified as one of the following types:
- 4.2 Liquid Flowmeters
- 4.3 Liquid Flow Measurement Methods. Liquid flow measurement methods that are within the scope of this standard are listed in Table 4-1. Each of these liquid flow measurement methods are described in Section 7.
- 5. Requirements [Go to Page]
- 5.1 Test Plan. The test plan shall be one of the following options:
- 5.2 Values to Be Determined and Reported. Values to be determined and reported if specified in the test plan in Section 5.1 shall use the units of measure listed in Table 5-1 unless otherwise specified in the test plan.
- 5.3 Test Requirements
- 6. Instruments [Go to Page]
- 6.1 Instrumentation Requirements for All Measurements
- 6.2 Temperature Measurements. If temperature measurements are required by the test plan in Section 5.1, the measurement system accuracy shall be within the following limits unless otherwise specified in the test plan:
- 6.3 Pressure Measurements
- 6.4 Time Measurements. Time measurement system accuracy shall be within ±0.5% of the elapsed time measured, including any uncertainty associated with starting and stopping the time measurement unless (a) otherwise specified in the test plan in Secti...
- 6.5 Mass Measurements. If mass measurements are required by the test plan in Section 5.1, the measurement system accuracy shall be within ± 0.2% of the reading unless otherwise specified in the test plan.
- 7. Liquid Flow Measurement Methods [Go to Page]
- 7.1 Constraint on All Liquid Flow Rate Measurement Methods. A selected liquid flow measurement plane (a) shall exceed 10 inside pipe diameters downstream of an obstruction or any change in the liquid flow direction and (b) shall exceed 5 inside pipe ...
- 7.2 Coriolis Flowmeters. Coriolis liquid flowmeters provide direct measurement of liquid mass flow rates. In a Coriolis flowmeter, the liquid flows through a vibrating sensor tube within the meter. An electromagnetic coil located on the sensor tube v...
- 7.3 Thermal Flowmeters. Thermal flowmeters provide direct measurement of liquid mass flow rates. The basic elements of thermal mass flowmeters are two temperature sensors that are located on opposite sides of a known heat source that supplies a const...
- 7.4 Orifice, Flow Nozzle, and Venturi Tube Flowmeters. Orifices, flow nozzles, and venturi tubes are liquid flowmeters that are based on empirical correlations of pressure differential to liquid flow rates. ASME PTC 19.5 6 and ASME MFC-3M 7 describe ...
- 7.5 Turbine Flowmeters. Turbine flowmeters are volumetric flowmeters that have a turbine rotor suspended on low-friction bearings in the liquid stream. The rotational speed of the turbine is a linear function of the average liquid velocity and is the...
- 7.6 Variable-Area Flowmeters. Variable-area flowmeters are volumetric flowmeters that consist of a float that is free to move vertically inside a tapered transparent tube that has a graduated scale as illustrated in Figure 7-4. The liquid to be meter...
- 7.7 Ultrasonic Flowmeters. Ultrasonic flowmeters measure liquid flow velocity. Clamp-on ultrasonic flowmeters measure liquid velocity within a pipe or tube without being inserted into the flowstream. Ultrasonic flowmeters use the transit-time method ...
- 7.8 Vortex-Shedding Flowmeters. Vortex-shedding flowmeters are used to determine liquid velocities. Piezoelectric methods, strain-gage methods, or hot-film methods are used to sense dynamic pressure variations created by vortex shedding. The operatin...
- 7.9 Drag-Force Flowmeters. Drag-force flowmeters determine liquid velocity. Piezoelectric or strain-gage methods are used to sense dynamic drag-force variations. A body immersed in a flowing liquid is subjected to a drag force given by Equation 7-8 i...
- 7.10 Magnetic Flowmeters. Magnetic flowmeters operate on the principle of Faraday’s law of induction, which states that the electromotive force induced in a circuit equals the negative of the time rate of change of the magnetic flux through the cir...
- 7.11 Positive-Displacement Flowmeters. Positive-displacement flowmeter types are gear, piston, and rotating vane. These flowmeters operate on a geometric principle using a known displacement volume divided by the cycle time to fill and evacuate that ...
- 7.12 Pitot-Static Tube Liquid Flow Measurement Methods. Figure 7-5 shows an example pitot-static tube construction and the connections to manometers or pressure transducers. Sections 7.12.1, 7.12.2, and 7.12.3 describe three different methods to dete...
- 8. Uncertainty Requirements [Go to Page]
- 8.1 Post-Test Uncertainty Analysis. A post-test analysis of the measurement system uncertainty, performed in accordance with ASME PTC 19.1 2, shall accompany each liquid flow measurement if specified in the test plan in Section 5.1. Installation effe...
- 8.2 Method to Express Uncertainty. All assumptions, parameters, and calculations used in estimating uncertainty shall be clearly documented prior to expressing any uncertainty values. Uncertainty shall be expressed as
- 9. Test Report [Go to Page]
- 9.1 Test Identification
- 9.2 Unit Under Test Description
- 9.3 Instrument Description
- 9.4 Measurement System Description
- 9.5 Test Conditions
- 9.6 Test Results. If specified in the test plan in Section 5.1:
- 10. References
- Informative Appendix A: Informative References and Bibliography [Go to Page]
- A1. References
- A2. Bibliography (Further Reading)
- Informative Appendix B: An Uncertainty Analysis Example for a Differential Pressure Flowmeter [Go to Page]
- B1. Calculate the Random and Systematic Standard Uncertainties For Each Parameter [Go to Page]
- B1.1 SI Units. Using Equations B-1 and B-2 and Table B-3, the following random and systematic standard uncertainties are calculated for each parameter:
- B1.2 I-P Units. Using Equations B-1 and B-2 and Table B-3, the following random and systematic standard uncertainties are calculated for each parameter:
- B2. Calculate the Random and Systematic Standard Uncertainties of the Working Fluid Density [Go to Page]
- B2.1 SI Units. Assuming a large degree of freedom, and using the previously calculated random and systematic standard uncertainties of t1 and p1, the expanded uncertainties are
- B2.2 I-P Units. Assuming a large degree of freedom and using the previously calculated random and systematic standard uncertainties of t1 and p1, the expanded uncertainties are
- B3. Calculate and Evaluate the Partial Derivative of the Mass Flow Rate for Each Parameter [Go to Page]
- B3.1 Derivations of the Partial Derivatives in SI Units. Skip this section if you are using a commercial equation solver.
- B3.2 Evaluation of Partial Derivatives in SI Units
- B3.3 Evaluation of Partial Derivatives in I-P Units. The calculated partial derivatives in I-P units are the same as in SI units; however, a factor of 0.47268 must multiply each partial derivative for the correct unit conversion.
- B4. Calculate the Random and Systematic Standard Uncertainties of the Mass Flow Rate [Go to Page]
- B4.1 SI Units
- B4.2 I-P Units
- B5. Calculate the Combined and Expanded Uncertainties of the Mass Flow Rate [Go to Page]
- B5.1 SI Units
- B5.2 I-P Units
- Informative Appendix C: Information Regarding Liquid Flow Measurement Uncertainties for Installations That do not Meet the Flowmeter Manufacturer’s Requirements [Go to Page]
- C1. Introduction
- C2. Previous Research Results and Technical Papers [Go to Page]
- C2.1 Technical Paper: Flowmeter Installation Effects—Wild Claims, Bright Ideas, and Stark RealitiesA6. The authors of this 1995 paper describe an eight-year project sponsored by a NIST-industry consortium that addressed the pipe flow distortions pr...
- C2.2 Laser Doppler Velocimeter Studies of the Pipe Flow Produced by a Generic HeaderA7. This 1995 paper reported laser Doppler velocimeter measurements for the pipe flows produced downstream of a header with and without a conventional 19-tube concent...
- C2.3 Summary Report of NISTs Industry-Government Consortium Research Program on Flowmeter Installation Effects: The 45 Degree ElbowA8. This 1994 report describes the effects of a conventional 45- degree elbow and includes discussion regarding a 19-tu...
- C2.4 Pipe Elbow Effects on the V-Cone FlowmeterA9. This 1993 paper presents installation effects on a special type of flowmeter with baseline comparisons to orifice plate differential pressure flowmeters.
- Informative Appendix D: Flowmeter Accuracy Comparisons [Go to Page]
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