An orifice meter installed in a pipeline is primarily used to measure which quantity reliably (after proper calibration)?

Introduction / Context:Differential head meters such as orifice meters, venturimeters, and flow nozzles are ubiquitous in industry. They create a known relationship between pressure drop and flow rate, enabling robust discharge measurements with appropriate coefficients and calibration.

Given Data / Assumptions:

• Concentric orifice plate with known beta ratio (d/D).
• Steady, incompressible flow; pressure taps upstream and downstream of the plate.
• Discharge coefficient Cd determined by standards or calibration.

Concept / Approach:Bernoulli plus continuity across the orifice section relates pressure drop to velocity through the throat area. The volumetric discharge Q is then Q = Cd * A2 * sqrt[2 * Δp / (rho * (1 − beta^4))], where A2 is the orifice area and beta is diameter ratio. With Cd known, Q follows from measured Δp.

Step-by-Step Solution:Measure pressure differential Δp using taps and a manometer/transducer.Compute throat velocity and multiply by throat area.Apply discharge coefficient Cd to correct for losses and non-idealities.

Verification / Alternative check:Comparison against volumetric tank tests confirms the orifice meter’s Q accuracy within prescribed ranges of Reynolds number and beta ratio when standards are followed.

Why Other Options Are Wrong:Static pressure: a pressure gauge alone does this; orifice meter depends on Δp.Average speed independent of area: discharge requires area * velocity.Local vena-contracta velocity: not directly measured by the pressure taps.Density: not directly measured; it must be known or inferred.

Common Pitfalls:

• Using incorrect Cd outside the calibration Reynolds number range.
• Ignoring temperature and fluid property variations affecting rho and Cd.

Final Answer:Volumetric discharge (flow rate)