# Pipe flow calculators

## Venturi tube calculator

#### Calculator Description

Venturi tube calculator can be used for calculating of actual flow rate through Venturi tube used as flow meter, for measured pressure drop in the tube and can also be used for Venturi tube sizing.

• Calculate:

• Flow rate for known Venturi size and pressure difference
• Flow velocity in the Venturi inlet and throat
• Discharge coefficient for compressible flow
• Gas expansion coefficient for compressible flow
• Input:

• Pressure difference at inlet and throat of Venturi tube
• Venturi inlet and throat diameter
• Density
• Viscosity

#### Calculator Features

• Conversion between volumetric and weight flow rate
• Calculation of Reynolds number included
• Applicable for non-compressible liquids and compressible perfect gases
• Pressure ratio p2/p1 must be equal or greater than 0.75
• For single-phase fluid, subsonic, non-pulsating flow
• ISO 5167 based calculation

Venturi tube is used as flow meter in piping system and where Venturi effect is required. Due to the change in diameter from inlet to throat mean velocity is changing while weight flow rate remains constant.

As total pressure remains mainly constant, part of static pressure is transformed into dynamic pressure from inlet to throat and pressure drop is created. This is called Venturi effect. Measuring static pressure on the inlet and on the throat - pressure drop, with this calculator, flow rate can be calculated, based on the energy conservation law and Bernoulli theorem.

For calculation of flow rate through Venturi tube in this calculator coefficient of discharge is calculated, as well as values of Reynolds number and mean velocity on the inlet and the throat of Venturi tube.

Calculator can also be used for Venturi effect analysis which is exploited in many appliances like Venturi vacuum pump, gas burners, wine aerator, aspirators, grills etc. Limiting factor for Venturi effect is when flow reaches chocked flow and mean velocity is close to local speed of sound.

Calculation of gas flow with higher pressure drop and flow close or equal to choked flow conditions gas discharge calculator should be used.

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

• 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:

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

Limits of use for Venturi tube with machined convergent section:

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

If you would like to use the calculator, but actually can't see the blue CALCULATOR button in the upper left part of the page than please read instructions.

Q: Calculate flow rate of air flowing through Venturi tube with bigger diameter of 200 mm and throat diameter of 100 mm, at 288 K. Measured pressures in front and in the throat of Venturi tube is 104000 Pa and 101325 Pa.

A: Calculation setup:
Flowing fluid: gas
Input one from following two:
p2 - absolute pressure in Venturi throat
T - temperature
ni - kinematic viscosity
Enter values:
D1 = 200 mm
D2 = 100 mm
p1 = 104000 Pa (absolute)
p2 = 101325 Pa (absolute)
ni = 13.4 mm2/s
T = 288 K
R = 287 J/kgK
kappa = 1.4
select Venturi type - welded tube

Q: Calculate flow rate of water flowing through Venturi tube with bigger diameter of 200 mm and throat diameter of 100 mm. Measured pressures in front and in the throat of Venturi tube is 108000 Pa and 100000 Pa.

A: Calculation setup:
Calculate for: liquid
Input one from following two:
p2 - absolute pressure in Venturi throat
ni - kinematic viscosity
Enter values:
D1 = 200 mm
D2 = 100 mm
p1 = 108000 Pa (absolute)
p2 = 100000 Pa (absolute)
ni = 1.006 mm2/s
rho = 1000 kg/m3
select Venturi type - welded tube

Q: Calculate flow rate of water flowing through Venturi tube with bigger diameter of 150 mm and throat diameter of 100 mm. Measured pressures in front and in the throat of Venturi tube is 108000 Pa and 100000 Pa. Venturi tube is machined.

A: Calculation setup:
Calculate for: liquid
Input one from following two:
p2 - absolute pressure after the orifice
ni - kinematic viscosity
Enter values:
D1 = 150 mm
D2 = 100 mm
p1 = 108000 Pa (absolute)
p2 = 100000 Pa (absolute)
ni = 1.006 mm2/s
rho = 1000 kg/m3
select Venturi type - machined tube

Equation used for flow through Venturi tube calculation:

Read more about used theory on flow in valves and fittings page.

If you experience problems with calculator start try to find answers on instructions page.

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