Book contents
- Front Matter
- Contents
- Preface
- Acknowledgments
- Nomenclature
- Chapter 1 Introduction
- Chapter 2 Fluid Mechanics Essentials
- Chapter 3 Specification, Selection, and Audit
- Chapter 4 Calibration
- Chapter 5 Orifice Plate Meters
- Chapter 6 Venturi Meter and Standard Nozzles
- Chapter 7 Critical Flow Venturi Nozzle
- Chapter 8 Other Momentum-Sensing Meters
- Chapter 9 Positive Displacement Flowmeters
- Chapter 10 Turbine and Related Flowmeters
- Chapter 11 Vortex-Shedding, Swirl, and Fluidic Flowmeters
- Chapter 12 Electromagnetic Flowmeters
- Chapter 13 Ultrasonic Flowmeters
- Chapter 14 Mass Flow Measurement Using Multiple Sensors for Single- and Multiphase Flows
- Chapter 15 Thermal Flowmeters
- Chapter 16 Angular Momentum Devices
- Chapter 17 Coriolis Flowmeters
- Chapter 18 Probes for Local Velocity Measurement in Liquids and Gases
- Chapter 19 Modern Control Systems
- Chapter 20 Some Reflections on Flowmeter Manufacture, Production, and Markets
- Chapter 21 Future Developments
- Bibliography
- A Selection of International Standards
- Conferences
- References
- Index
Chapter 7 - Critical Flow Venturi Nozzle
Published online by Cambridge University Press: 22 September 2009
- Front Matter
- Contents
- Preface
- Acknowledgments
- Nomenclature
- Chapter 1 Introduction
- Chapter 2 Fluid Mechanics Essentials
- Chapter 3 Specification, Selection, and Audit
- Chapter 4 Calibration
- Chapter 5 Orifice Plate Meters
- Chapter 6 Venturi Meter and Standard Nozzles
- Chapter 7 Critical Flow Venturi Nozzle
- Chapter 8 Other Momentum-Sensing Meters
- Chapter 9 Positive Displacement Flowmeters
- Chapter 10 Turbine and Related Flowmeters
- Chapter 11 Vortex-Shedding, Swirl, and Fluidic Flowmeters
- Chapter 12 Electromagnetic Flowmeters
- Chapter 13 Ultrasonic Flowmeters
- Chapter 14 Mass Flow Measurement Using Multiple Sensors for Single- and Multiphase Flows
- Chapter 15 Thermal Flowmeters
- Chapter 16 Angular Momentum Devices
- Chapter 17 Coriolis Flowmeters
- Chapter 18 Probes for Local Velocity Measurement in Liquids and Gases
- Chapter 19 Modern Control Systems
- Chapter 20 Some Reflections on Flowmeter Manufacture, Production, and Markets
- Chapter 21 Future Developments
- Bibliography
- A Selection of International Standards
- Conferences
- References
- Index
Summary
INTRODUCTION
This meter uses a fascinating effect that occurs when gas flows at very high velocity through a nozzle. As the gas is sucked through the nozzle, the velocity increases as the cross-section of the nozzle passage decreases toward the throat. At the throat, the maximum achievable velocity is sonic – the speed of sound. Downstream of the throat, the velocity will either fall again returning to subsonic or will rise and become supersonic. In normal operation of the nozzle, the supersonic region is likely to be small and to be followed by a shock wave that stands across the divergent portion of the nozzle and causes the gas to drop, very suddenly, from supersonic to subsonic. The existence of a shock wave does not mean that one will hear a “supersonic bang”! Such bangs are usually caused by moving shock waves carried forward by high speed aircraft.
The fascinating effect of sonic conditions at the throat is that changes in the flow downstream of the throat have no effect on conditions upstream. The sonic or critical condition, as it is called, appears to block any information that is trying to penetrate upstream. A simple picture of this is that the messengers carrying such information travel at the speed of sound and so are unable to make any headway over the fast flowing gas stream.
- Type
- Chapter
- Information
- Flow Measurement HandbookIndustrial Designs, Operating Principles, Performance, and Applications, pp. 140 - 152Publisher: Cambridge University PressPrint publication year: 2000