Description

p₁ - inlet pressure

Absolute pressure at the Venturi inlet

p₂ - throat pressure

Absolute pressure at the Venturi throat

Δp - pressure drop

Measured pressure difference

D₁ - inlet diameter

Venturi internal inlet diameter

D₂ - throat diameter

Venturi throat diameter

e - expansion factor

Coefficient used for compressible flow calculation

C - coefficient of discharge

Coefficient used for Venturi tube based on ISO 5167

R_eD - inlet Reynolds

Reynolds number calculated in front of the Venturi tube

R_ed - throat Reynolds

Reynolds number calculated at the Venturi tube throat

q₁ - volumetric flow rate

Fluid flow rate in terms of units of volume per unit of time on the inlet conditions

q - standard flow

Flow rate at standard conditions. Used only if the selected fluid is gas.

ṁ - mass flow rate

Fluid flow rate in terms of units of mass per unit of time

V₁ - upstream velocity

Flow velocity at the Venturi tube inlet where flow diameter is D₁

T₁ - upstream temperature

Fluid temperature for gas density calculation based on the ideal gas state equation

ρ₁ - upstream density

Fluid density at the Venturi inlet in terms of mass per unit of volume

R - gas constant

Gas constant in terms of energy per unit of mass and temperature, for gas density calculation using ideal gas state equation

κ - isentropic coefficient

Specific heat ratio

ν - kinematic viscosity

Result of fluid particles colliding to each other and moving at different velocities in terms of area per square unit of time

μ - dynamic viscosity

Result of fluid particles colliding to each other and moving at different velocities in terms of mass per square unit of distance and time

Calculation setup

Select Venturi tube type based on its manufacturing technology

Welded

Venturi tube manufactured by welding

Casted

Venturi tube manufactured by casting

Machined

Venturi tube manufactured by machining

Select value to input. You should enter selected one. The other one will be calculated

p₂

pressure in the throat of the Venturi tube

Δp

measured pressure difference in front and in the throat of the Venturi tube

Select value to input. You should enter selected one. The other one will be calculated

ν

kinematic viscosity

μ

dynamic viscosity

Select value to input. Available only if gas is selected. You should enter selected one. The other one will be calculated

T₁

upstream temperature.

ρ₁

upstream density.

Select fluid type

Gas

for compressible flow where ideal gas state equation is applicable

Liquid

for incompressible flow of liquids

Application of ISO 5167 constraints

ISO constraints

Deselect if you don't want to check if the Venturi tube and the flow conditions are within the limits of the ISO standard.

Why should you use this calculator?

Use this calculator to quickly calculate the actual flow rate through the Venturi tube flow meter with only a few inputs. This calculator performs the flow rate calculation from the measured pressure difference caused by the flow contraction in the throat of the Venturi tube.

Due to the contraction in the diameter from the inlet to the throat of the Venturi tube, the flow velocity is changing while flow rate remains constant. That change in flow velocity is creating the increase of the dynamic pressure and drop of the static pressure, as total pressure remains uniform, according to the conservation law.

The change of the static pressure can be easily measured. That measured value is the input value for the calculation of the flow rate in the Venturi tube. You should measure pressure in front of the Venturi and the Venturi's throat and use that value in the calculator.

This calculator also calculates total pressure drop created by the Venturi tube, although it is much lower than in other pressure differential metering devices like an orifice.

You can use the calculator for the Venturi effect (change of the static pressure due to the flow stream contraction) analysis, also. Many devices like Venturi vacuum pump, gas burners, wine aerator, aspirators, grills, and others use Venturi effect for their operation. These devices are creating the drop in static pressure, and that pressure change is inducing the flow of the other fluid.

When is this calculator suitable?

The calculator is relevant for a subsonic flow single-phase liquid or ideal gases. It is not applicable for pulsating flow, or non-steady flow when the flow rate is changing in time.

When is this calculator not relevant?

This calculator is not suitable for flow of multiphase fluids, like a stream of liquids that contain solid particles or stream of liquids that contain undissolved gases. Also, it is not suitable for gases that are not ideal, i.e., gases that don't relate to the ideal gas law.

Limiting factor for Venturi effect is when the flow reaches chocked flow and mean velocity is close to the local speed of sound.

What has to be understood to perform the calculation?

To calculate flow rate, you have to enter the Venturi tube inlet and throat diameter, together with fluid properties - density and viscosity.

For a gas as flowing fluid, instead of the density, you can enter gas constant, pressure and temperature at actual conditions. Density is then calculated using a perfect gas state equation.

You should enter density on real flow conditions - real pressure and real temperature.

How is the calculation executed?

The calculator is doing calculation according to ISO 5167-4.

You can expect to have accurate and reliable results solely if the Venturi tube satisfies the requirements from the standard.

What are the standard ISO 5137-4 conditions?

For the flow of a perfect gas, the pressure reduction produced by the Venturi tube (p2/p1) must be higher than 0.75.

Limits of use for Venturi tube with an "as cast" convergent section are:

100 mm < D < 800 mm
0.3 < β < 0.75
2x10⁵ < ReD < 2x10⁶

Limits of use for Venturi tube with a rough welded sheet iron convergent section are:

200 mm < D < 1200 mm
0.4 < β < 0.7
2x10⁵ < ReD < 2x10⁶

Limits of use for Venturi tube with machined convergent section are:

50 mm < D < 250 mm
0.4 < β < 0.75
2x10⁵ < ReD < 1x10⁶

where is:
β - diameter ratio d/D

What happens if a calculation is not within these limits?

If the Venturi tube characteristics or flow conditions are not according to the ISO 5167-4 calculator presents the message. If you still want to perform calculation regardless of the conditions in the standard, you can choose not to use ISO constraints in the calculation.