Home>ASME standards>ASME MFC-12M-2006 pdf download

ASME MFC-12M-2006 pdf download

ASME MFC-12M-2006 pdf download.Measurement of Fluid Flow in Closed Conduits Using Multiport Averaging Pitot Primary Elements.
ASME MFC-8M, Connections for Pressure Signal Trans- missions Between Primary and Secondary Devices ASME MFC-9M, Measurement of Liquid Flow in Closed Conduits by Weighing Method ASME MFC-10M, Method for Establishing Installation Effects on Flowmeters Publisher: The American Society of Mechanical Engineers (ASME), Three Park Avenue, New York, NY 10016-5990; Order Department: 22 Law Drive, P.O. Box 2300, Fairfield, NJ 07007-2300 ISO 4185, Measurement of Liquid Flow in Closed Conduits — Weighing Method ISO 5168, Measurement of Fluid Flow — Evaluation of Uncertainties ISO 8316, Measurement of Liquid Flow in Closed Conduits — Method by Collection of the Liquid in a Volumetric Tank Publisher: International Organization for Standardiza- tion(ISO), 1 ruedeVarembe´,Case Postale 56,CH-1211, Gene`ve 20, Switzerland/Suisse 4 OPERATING PRINCIPLES 4.1 Description of Operation The multiport averaging Pitot primary flow element or averaging Pitot tube (APT) is similar to the conven- tional single point Pitot tube in operation, but differs in construction. It is typically designed as a strut, or cylin- der (the cross section of the cylinder is not necessarily circular), that is inserted across the circular pipe or con- duit on a diameter. Some APT designs have more than one strut to achieve a more representative sample of the fluid velocity in the pipe or conduit (see Nonmandatory Appendix A). The strut has ports that sense the total velocity head (total pressure), and a reference, or low pressure. In some APT designs the reference pressure is measured at the pipe wall. Figures 1 and 2 show two commonly used methods for sensing the total pressure and reference pressure. The sensed pressure(s) are con- veyed through isolated passages, or chambers in the cylinder to the exterior of the assembly, where there are connections to the secondary device. By combining the individually sensed pressures from its sensing ports, the APT produces a differential pressure that can be related to the average fluid velocity in the pipe or conduit. 4.2 Bernoulli’s Equation As with other differential pressure-based flow pri- mary elements, the underlying principle for the APT sensor is the application of the momentum equation from basic fluid theory. Using the assumptions for steady state, inviscid, and incompressible flow along a streamline, the equation reduces to the Bernoulli equa- tion (see Nonmandatory Appendix B)
7.1 Velocity Profile Manufacturers define the performance of their APT for reference profile conditions with specific upstream and downstream lengths of straight pipe. These lengths are chosen to ensure the performance of the APT. Under nonreference conditions, upstream velocity profiles may affect the velocity profile at the flow measurement point and influence the performance. The manufacturer should be consulted for the sensitivity of the APT to nonreference flow conditions. In some cases, the use of a flow conditioner may restore the velocity profile to the reference profile. 7.2 Upstream and Downstream Pipe Length Requirements The minimum upstream and downstream straight lengths ofpipe required to meetthe performance specifi- cation of the APT should be stated by the manufacturer. The minimum lengths required downstream of different pipe fittings may vary for each APT and piping configu- ration. When the flow measurement application or installa- tion configuration does not match one of the manufac- turer’s listed applications and installations, the flowmeter manufacturer should be consulted. If the manufacturer cannotprovide sufficientguidance, in-situ calibration may be considered. In-situ calibration establishes the flow coefficient of the APT and uncertainty under actual operating condi- tions. If in-situ calibration is performed, the calibration should be done in accordance with acceptable standards as listed in section 3. If in-situ calibration is not possible, the effect of installation can be reduced by performing a flow laboratory calibration of the meter replicating the actual upstream and downstream piping installations. 7.3 Alignment and Orientation 7.3.1 Alignment. The manufacturer shall specify the limits of the allowable angular tolerances for the installation of the APT. Deviation of the APT primary element in any angular alignment from the allowable limits can result in erroneous flow measurement. 7.3.2 Orientation. Manufacturers shall specify pre- ferred APT locations and orientations with respect to the horizontal or vertical axis of the flow conduit. These preferred orientations may depend on the fluid being measured. 7.4 Conduit Internal Surface Condition Surface roughness of the flow conduit can affect the velocitydistribution atthe meteringlocation. The manu- facturer should advise the user on the effects of internal pipe surfaces. In some cases, buildup of mineral or other deposits on the internal wall of the conduit may alter the velocity distribution or obscure the APT sensing ports.

Related PowerPoint Templates

Template Categories
Popular Tags