Open-channel discharge measurement Liquid discharge from a tank or reservoir (free surface) cannot be measured using which of the following primary devices?

Introduction / Context:
Measuring volumetric flow (discharge) from tanks, sumps, and reservoirs often involves free-surface hydraulics rather than pressurized pipe flow. Selection of a suitable primary element is crucial for accuracy and practicality. This question focuses on which device is not used for such open-channel or free-discharge situations.

Given Data / Assumptions:

• Flow leaves a tank/reservoir with a free surface (non-pressurized).
• Head-discharge relationships are applied in open-channel context.
• We consider standard textbook devices.

Concept / Approach:
Weirs and notches are classic open-channel metering devices placed in flumes or at channel/tank exits, using head over crest to compute discharge. Mouthpieces (short tubes attached to orifices on a tank wall) are also associated with tank discharge measurement via empirical coefficients. In contrast, orificemeters are differential-pressure flow meters installed in closed, pressurized pipes with well-developed flow; they are not used on free-surface tanks/reservoirs for direct discharge metering.

Step-by-Step Solution:

Verification / Alternative check:
Hydraulics texts classify weirs/notches under open-channel measurement and orificemeters under incompressible pipe-flow DP meters.

Why Other Options Are Wrong:

• Weirs / Notches: Designed precisely for free-surface discharge measurement.
• Mouthpieces: Applied on tank outlets with empirical discharge coefficients.

Common Pitfalls:
Confusing a tank orifice (with or without mouthpiece) with an orificemeter assembly used in pipes with pressure taps and flange taps.

Final Answer:
Orificemeters