How does a venturi flow meter measure flow and what principle does it rely on?

How does a venturi flow meter measure flow and what principle does it rely on?

• A. A throat constriction causes a pressure drop; applying Bernoulli's principle yields Q in terms of ΔP and fluid density.
• B. It uses a turbine wheel to measure rotation speed.
• C. It measures flow by heating a section of fluid.
• D. It relies on buoyancy of a float.

Answer: (A)

Venturi meters rely on a smooth constriction to speed up the fluid, which makes the static pressure drop at the throat. By measuring the pressure difference between the upstream section and the throat and applying Bernoulli’s principle together with conservation of mass, you relate that pressure drop to the fluid velocity and thus to the volumetric flow rate. The geometry fixes how ΔP translates to flow, so the flow is proportional to the throat area and to the square root of the pressure drop divided by density (with a factor that depends on the area ratio). In ideal terms, Q ≈ C A2 sqrt(2 ΔP / [ρ(1 − β^4)]) where β is A2/A1 and C is a discharge coefficient near 1. Other devices described (turbine wheels, heating/cooling sensors, or floats) use different mechanisms and do not rely on this pressure-difference–Bernoulli relationship, which is why this method uniquely identifies a Venturi flow meter.

Venturi meters rely on a smooth constriction to speed up the fluid, which makes the static pressure drop at the throat. By measuring the pressure difference between the upstream section and the throat and applying Bernoulli’s principle together with conservation of mass, you relate that pressure drop to the fluid velocity and thus to the volumetric flow rate. The geometry fixes how ΔP translates to flow, so the flow is proportional to the throat area and to the square root of the pressure drop divided by density (with a factor that depends on the area ratio). In ideal terms, Q ≈ C A2 sqrt(2 ΔP / [ρ(1 − β^4)]) where β is A2/A1 and C is a discharge coefficient near 1. Other devices described (turbine wheels, heating/cooling sensors, or floats) use different mechanisms and do not rely on this pressure-difference–Bernoulli relationship, which is why this method uniquely identifies a Venturi flow meter.