Which principle underlies a differential pressure flow meter and how does density affect the computed flow?

Which principle underlies a differential pressure flow meter and how does density affect the computed flow?

• A. Bernoulli's principle; Q ∝ sqrt(ΔP/ρ); density affects the relationship and must be accounted for.
• B. Hooke's law; Q ∝ ΔP; density has no effect.
• C. Ohm's law; Q ∝ ΔP/ρ; density effect incorrect.
• D. Archimedes' principle; density only matters for buoyancy.

Answer: (A)

Differential pressure flow meters rely on Bernoulli's principle: when fluid is forced through a constriction, its velocity increases and the pressure drops. The measured pressure difference is tied to the flow velocity, and the flow rate ends up being proportional to the square root of the pressure drop divided by density. This means density directly affects the computed flow: for the same pressure drop, a denser fluid produces a smaller velocity, so the flow rate estimate changes unless density is accounted for in the calculation or calibration. In practice, you calibrate for a known density and apply corrections if density varies (such as with temperature changes or gas behavior). The other options don’t describe how a differential pressure meter relates pressure drop to flow: Hooke's law is about solid deformation, Ohm's law governs electrical currents, and Archimedes' principle concerns buoyancy rather than the pressure-velocity relationship in flowing fluids.

Differential pressure flow meters rely on Bernoulli's principle: when fluid is forced through a constriction, its velocity increases and the pressure drops. The measured pressure difference is tied to the flow velocity, and the flow rate ends up being proportional to the square root of the pressure drop divided by density. This means density directly affects the computed flow: for the same pressure drop, a denser fluid produces a smaller velocity, so the flow rate estimate changes unless density is accounted for in the calculation or calibration. In practice, you calibrate for a known density and apply corrections if density varies (such as with temperature changes or gas behavior). The other options don’t describe how a differential pressure meter relates pressure drop to flow: Hooke's law is about solid deformation, Ohm's law governs electrical currents, and Archimedes' principle concerns buoyancy rather than the pressure-velocity relationship in flowing fluids.