Abstract
The conventional quasi-steady theory for the behaviour of meters in pulsating flow is that at any instant the differential pressure is only dependent on the acceleration of the flow due to the contraction and is given by the steady flow relationship. The analysis presented in this thesis is based on a quasi-steady theory modified to take into account the additional instantaneous differential pressure due to the temporal acceleration of the flow. Relationships are derived for metering errors in terms of the r.m.s. amplitude of the differential pressure pulsation and a Strouhal Number dependent on the waveform of the velocity pulsation. To test the validity of the derived theoretical relationships the behaviour of square edge orifice plates with corner tappings and of venturi nozzles were investigated in pulsating air flows. A piston pulsator was built on which the stroke can be varied to obtain a required pulsation amplitude while the machine is running at frequencies up to 50 Hz. The results of the tests showed that, although there were some discrepancies, the theoretical relationships were basically sound. It was found that it was possible to define when pulsations were significant in terms of the r.m.s. amplitude of the differential pressure fluctuation. It was also possible to determine an effective Strouhal Number when temporal inertia effects became significant. No basic differences in the behaviour of the two types of meter were detected but certain predictable effects due to compressibility were observed in tests on the venturi nozzles. The techniques for reducing metering errors due to pulsations are reviewed in the light of the analysis and experimental results. Criteria by which the pulsation conditions can be properly assessed and appropriate courses of action for reducing metering error are suggested.