# Venturi tube flow rate calculator

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

As total pressure remains mainly constant in Venturi tube, 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 Venturi meter 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 flow meters, 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.

Flow through Venturi tube calculator can be used for both liquids and gases.
Calculator is applicable for subsonic flow and single phase fluid.
Gas is considered as compressible and ideal. For gas flow, pressure ratio
p_{2}/p_{1} must be equal or greater than 0.75.
Calculator is not for pulsating flow.

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
- 2x10
^{5}< Re_{D}< 2x10^{6}

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

- 200 mm < D < 1200 mm
- 0.4 < β < 0.7
- 2x10
^{5}< Re_{D}< 2x10^{6}

Limits of use for Venturi tube with machined convergent section:

- 50 mm < D < 250 mm
- 0.4 < β < 0.75
- 2x10
^{5}< Re_{D}< 1x10^{6}

Flow rate through Venturi tube is calculated using:

where is:

*q*- flow rate*C*- flow coefficient*A*- cross section area*Δ p*- pressure drop*ρ*- density*g*- acceleration of gravity_{n}*h*- head loss_{L}

The values of *h _{L}* and

*Δ p*are measured differential static head or pressure before and after the Venturi tube. Values for coefficient of discharge or flow coefficient (

*C*or

*C*) can be obtained based on applicable standards like ISO 5167 or similar ASME standards. Bellow are flow coefficients from ISO 5167:

_{d}- Venturi tubes with "as cast" convergent section
*C*=0.984_{d} - Venturi tubes with a machined convergent section
*C*=0.995_{d} - Venturi tubes with a rough-welded sheet-iron convergent section
*C*=0.985_{d}

Relation between flow coefficient and discharge coefficient (*C* and *C _{d}*) is given bellow:

where is:

*C*- flow coefficient*C*- coefficient of discharge_{d}*β*- diameter ratio*d*_{1}/d_{2}

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