ASME MFC-12M:2006 pdf download.Measurement of Fluid Flow in Closed Conduits Using Multiport Averaging Pitot Primary Elements.
4 OPERATING PRINCIPLES
4.1 Description of Operation
The multiport averaging Pilot primary flow element or averaging Pitot tube (APT) is similar to the conventional single point Pitot tube in operation, but differs in construction. It is typically designed as a strut, or cylinder (the cross section of the cylinder is not necessarily circular), that is inserted across the circular pipe or conduit 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 Al’T 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 conveyed 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 primary 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 equation (see Nonmandatory Appendix 13).
4.1 Description of Operation
The multiport averaging Pilot primary flow element or averaging Pitot tube (APT) is similar to the conventional single point Pitot tube in operation, but differs in construction. It is typically designed as a strut, or cylinder (the cross section of the cylinder is not necessarily circular), that is inserted across the circular pipe or conduit 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 Al’T 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 conveyed 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 primary 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 equation (see Nonmandatory Appendix 13).
