Venturi Tube Flow Calculator
Calculate flow through a classical venturi tube from its differential pressure. The discharge coefficient follows ISO 5167-4 for the chosen construction, and gases include the expansibility factor.
- β = 0.6000, C = 0.995
- qm = C ÷ √(1 − β⁴) × ε × π/4 × d² × √(2ΔPρ) = 76.218 kg/s
Venturi Flow Equation
ε = √[ κτ2/κ/(κ − 1) × (1 − β⁴)/(1 − β⁴τ2/κ) × (1 − τ(κ−1)/κ)/(1 − τ) ], τ = p2/p1
Worked example
Water through a machined venturi, D = 200 mm, d = 120 mm (β = 0.6), at 200 mbar: qm ≈ 274,000 kg/h (about 275 m³/h).
Frequently Asked Questions
Why is the venturi discharge coefficient close to 1?
The smooth convergent section guides the flow without a vena contracta, so the actual flow is almost the theoretical flow.
When should I use a venturi instead of an orifice?
On large lines, dirty fluids or where pressure loss is costly. Venturis cost more but need less straight pipe and recover more pressure.
What is the expansibility factor for gas?
It corrects for gas expansion as pressure falls into the throat. It is 1 for liquids and slightly less than 1 for gases.
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