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

Difficulty: Easy

Correct Answer: Volumetric discharge (flow rate)

Explanation:


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)

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