Nozzle and Venturi nozzle flow calculator

flow rate measurement calculator

online since 2011

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Calculation setup
Flow rates and velocities
Nozzle dimensions and coefficients
Fluid properties

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p1 - inlet pressure
Absolute pressure in front of the nozzle
p2 - throat pressure
Absolute pressure at the nozzle throat
Δp - pressure drop
Measured pressure difference
Δω - pressure loss
That can't be recovered after the nozzle
D1 - inlet diameter
Nozzle internal inlet diameter
D2 - throat diameter
Nozzle throat diameter
e - expansion factor
Coefficient used for compressible flow calculation
C - coefficient of discharge
Coefficient used for nozzle based on ISO 5167
ReD - inlet Reynolds
Reynolds number calculated in front of the nozzle
Red - throat Reynolds
Reynolds number calculated at the nozzle throat
K - resistance coefficient
That you can use in pipeline calculation, as nozzle is creating local pressure losses in the pipeline
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 nozzle 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 nozzle 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 nozzle type based on its shape
Classic shape
Long radius
For less pressure drop
Venturi nozzle
Shaped like Venturi
Select value to input. You should enter selected one. The other one will be calculated
pressure downstream from the nozzle
measured pressure difference in front and after the nozzle
Select value to input. You should enter selected one. The other one will be calculated
kinematic viscosity
dynamic viscosity
Select value to input. Available only if gas is selected. You should enter selected one. The other one will be calculated
upstream temperature.
upstream density.
Select fluid type
for compressible flow where ideal gas state equation is applicable
for incompressible flow of liquids
Application of ISO 5167 constraints
ISO constraints
Deselect if you don't want to check if the nozzle and the flow conditions are within the limits of the ISO standard.

Why should you use this calculator?

Nozzles and Venturi nozzles are devices that are inserted in circular cross-section conduit to create a pressure difference of static pressure caused by the flow contraction in the throat of it. You can calculate flow rate using that pressure difference.

Due to the contraction in the diameter from the inlet to the throat of the nozzle, 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.

You can measure the change of the static pressure by measuring the pressure in the inlet and after the nozzle. That measured value is the input value for the calculation of the flow rate.

This calculator also calculates total pressure drop created by the nozzle. You can use this calculator for all three types of nozzles covered in standards: ISA 1932 nozzle, long radius nozzle, and Venturi nozzle. All three types differ from each other based on its shape. All nozzles have radius shaped convergent inlet with the cylindrical throat, and Venturi nozzle also has a divergent part as an outlet.

When is this calculator suitable?

You can use a nozzle and Venturi nozzle calculator for subsonic single-phase liquids or ideal gases. The calculator is not 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 perfect gas law.

Limiting factor for this calculator is when the flow reaches chocked flow and mean velocity is close to the local speed of sound. You can use gas discharge calculator for calculation of gas flow with a higher pressure drop and flow close or equal to choked flow conditions.

What else has to be known to perform the calculation?

To calculate flow rate, you have to enter the nozzle 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 an ideal gas state equation.

You should enter density on actual flow conditions, as well as real pressure and real temperature.

How is the calculation performed?

The calculator is doing calculation according to ISO 5167-3. You can expect to have accurate and reliable results solely if the device satisfies the requirements from the standard.

What are the standard ISO 5137-3 conditions?

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

Limits of use for nozzles are:

50 mm < D < 500 mm
0.3 < β < 0.8
7x104 < ReD < 107 for 0.3 < β < 0.44
2x104 < ReD < 107 for 0.44 < β < 0.80

Limits of use for long radius nozzles are:

50 mm < D < 630 mm
0.2 < β < 0.8
104 < ReD < 107

Limits of use for Venturi nozzles are:

65 mm < D < 500 mm
0.316 < β < 0.775
1.5x105 < ReD < 2x106

What happens if a calculation is not within these limits?

If the nozzle characteristics or flow conditions are not according to the ISO 5167-3 calculator presents the warning message. If you still want to perform calculation regardless of the states in the standard, you can choose not to use ISO constraints in the computation.

Available in download version

save/open multiple results
export to word and excel
print results
custom fluid properties
K factor for fittings, resistance coefficient
pipe surface roughness selection
select between gauge and absolute pressure
compressible isothermal flow
dry air isothermal flow
gas offtake flow
natural gas flow


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