Venturi Meters

8/24/13 VENTURI METERS

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VACUUM

VACUUM DISTILLATION

VACUUM DRYERS

VACUUM EJECTORS

VACUUM ELECTRIC FURNACES

VACUUM PUMP

VAN DER WAALS EQUATION

VAN DER WAALS EQUATION OF

STATE

VAN DER WAALS FORCES

VAN DER WAALS ISOTHERMS

VAN DRIEST'S DAMPING FORMULA

VAN DRIEST'S EXPRESSION FOR

TURBULENT VISCOSITY

VAN DRIEST'S MIXING LENGTH MODEL

VAN LAAR EQUATION

VAN'T HOFF EQUATION

VAN'T HOFF ISOTHERM

VANADIUM

VANE ANEMOMETERS

VAPOR ABSORPTION CYCLE

VAPOR BUBBLE, EQUILIBRIUM OF

VAPOR EXPLOSIONS

VAPOR PRESSURE

VAPOR PRESSURE THERMOMETER

(1)

(2)

(3)

(4)

VENTURI METERSReader-Harris, Michael J.

DOI: 10.1615/AtoZ.v.venturi_meters

Venturi meters are flow measurement instruments which use a converging section of pipe to give an increase in the flow

velocity and a corresponding pressure drop from which the flowrate can be deduced. They have been in common use for

many years, especially in the water supply industry.

The classical Venturi meter, whose use is described in ISO 5167-1: 1991, has the form shown in Figure 1

Figure 1. Classical Vetituri meter design. (From B. S. 7405 (1991) Fig. 3.1.4, with permission of B.S.I.)

For incompressible flow if the Bernoulli Equation is applied between two planes of the tappings,

where p, and are the pressure, density and mean velocity and the subscripts 1 and 2 refer to the upstream and

downstream (throat) tapping planes.

From continuity

where is the volumetric flowrate and D and d the pipe and throat diameters.

Combining Eqs. (1) and (2)

where is the diameter ratio, d/D. In reality, there is a small loss of total pressure, and the equation is multiplied by the

discharge coefficient, C, to take this into account:

where p is the differential pressure (p1 p2). The discharge coefficient of a Venturi meter is typically 0.985, but may be

even higher if the convergent section is machined. Discharge coefficients for uncalibrated Venturi meters, together with

corresponding uncertainties, are given in ISO 5167-1: 1991.

If the fluid being metered is compressible, there will be a change in density when the pressure changes from p1 to p2 on

passing through the contraction. As the pressure changes quickly, it is assumed that no heat transfer occurs and because

no work is done by or on the fluid, the expansion is isentropic. The expansion is almost entirely longitudinal and an

expansibility factor, , can be calculated assuming one-dimensional flow of an ideal gas:

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VAPOR PRESSURE, EQUILIBRIUM,

CHANGE WITH TEMPERATURE

VAPOR SHEAR STRESS EFFECTS

VAPOR SHEAR, EFFECT ON

CONDENSATION

VAPOR SORPTION REFRIGERATION

CYCLE

VAPOR-COMPRESSION

REFRIGERATION CYCLE

VAPOR-LIQUID EQUILIBRIUM

VAPOR-LIQUID SEPARATION

VAPORIZATION

VARIABLE AREA FLOWMETER

VARIABLE FLUID PROPERTIES

VARIABLE REFRACTIVE INDEX MEDIA

VARIABLE VISCOSITY EFFECTS

VARIATION OF FLUID PROPERTIES

VDI

VECTORS

VEHICLES INTERSECTION

VELOCITY BOUNDARY LAYER

VELOCITY DEFECT

VELOCITY HEAD

VELOCITY MEASUREMENT

VELOCITY OF LIGHT

VELOCITY OF SOUND

VELOCITY OF SOUND IN TWO-PHASE

MIXTURES

VELOCITY RATIO

VELOCITY, AVERAGE PHASE

VELOCITY, SUPERFICIAL

VENA CONTRACTA

VENTILATION

VENTURI EJECTORS

VENTURI METERS

VENTURI NOZZLE

VENTURI SCRUBBER

VENTURI TUBES

VEREIN DEUTSCHEUR INGENIEUR, VDI

VERTICAL SHAFT KILNS

VERTICAL THERMOSYPHON REBOILER

VIBRATION

VIBRATION IN HEAT EXCHANGERS

VIBRATION, FLOW INDUCED

VIENNA CONVENTION

VIEWFACTOR

VINYL CHLORIDE MONOMER

VIRIAL COEFFICIENT

VIRIAL EXPANSION

VIRTUAL MACHINE

VIRTUAL MEMORY

VISCOELASTIC FLUIDS

VISCOELASTIC SOLIDS

VISCOMETER

(5)

where is the pressure ratio, p2/p1, and the isentropic exponent. The expansibility factor is applied to the flow equation

in the same way as the discharge coefficient.

Various forms of construction of a Venturi meter are employed, depending on size, but all are considerably more expensive

than the orifice plate. However, because most of the differential pressure is recovered by means of the divergent outlet

section, the Venturi causes less overall pressure loss in a system and thus saves energy: the overall pressure loss is

generally between 5 and 20 per cent of the measured differential pressure. The Venturi meter has an advantage over the

orifice plate in that it does not have a sharp edge which can become rounded; however, the Venturi meter is more

susceptible to errors due to burrs or deposits round the downstream (throat) tapping.

The lengths of straight pipe required upstream and downstream of a Venturi meter for accurate flow measurement are

given in ISO 5167-1: 1991. These are shorter than those required for an orifice plate by a factor which can be as large as 9.

However, Kochen et al. show that the minimum straight lengths between a single upstream 90 bend and a Venturi meter

in the Standard are too short by a factor of about 3.

References

1. British Standards Institution (1991) Guide to selection and application of flowmeters for the measurement of fluid flow

in closed conduits, BS 7405.

2. International Organization for Standardization, Measurement of fluid flow by means of pressure differential devices

Part 1: Orifice plates, nozzles and Venturi tubes inserted in circular cross-section conduits running full. ISO 5167-1:

1991.

3. Kochen, G., Smith, D. J. M., and Umbach, A. (1989) Installation effects on Venturi tube flowmeters, Intech Engineers

Notebook, October 1989,41-43.

Number of views: 23715 Article added: 2 February 2011 Article last modified: 11 February 2011 Copyright 2010-2013 Back to top



VISCOPLASTIC BEHAVIOR OF METAL

POWDERS

VISCOSITY

VISCOSITY MEASUREMENT

VISCOSITY OF AIR

VISCOSITY OF BUBBLY MIXTURES

VISCOSITY OF GASES

VISCOUS DISSIPATION RATE

VISCOUS DISSIPATIVE FLUID

VISCOUS FINGERING MECHANISMS

VISIBILITY

VISIBLE LIGHT

VISUALIZATION OF DRYOUT

PHENOMENON

VISUALIZATION OF FLOW

VISUALIZATION OF STREAMLINES

VISUALIZING VORTEX FORMATION

VOID FRACTION

VOID FRACTION DISTRIBUTION

PATTERN

VOID FRACTION MEASUREMENT

VOID WAVE PROPAGATION

VOIDS

VOLATIZATION

VOLTERRA INTEGRAL EQUATIONS

VOLUME FILLING

VOLUME FORCES

VOLUME MEAN DIAMETER, VMD

VON KARMAN CONSTANT

VON KARMAN STREET

VON KARMAN VELOCITY

DISTRIBUTION

VON KARMAN VORTEX STREET

VON KARMAN, THEODORE (1881-

1963)

VORTEX

VORTEX BREAKDOWN

VORTEX CHAMBER

VORTEX EFFECTS

VORTEX EXCITATION OF TUBES

VORTEX FLOWMETERS

VORTEX GENERATORS

VORTEX INSTABILITY

VORTEX MIXER

VORTEX SEPARATORS

VORTEX SHEDDING

VORTEX STREET

VORTEX VIBRATIONS

VORTICAL FLOWS

VORTICES

VORTICITY

VORTICITY TRANSPORT EQUATION

VULCANISTATION

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