Primary purpose of manometers in fluid mechanics Manometers are most commonly used to measure which of the following?
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ADifference in pressure between two points
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BAtmospheric pressure only
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CVery low vacuum pressure exclusively
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DVelocity in open channels
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ETemperature-dependent pressure variations
Answer
Correct Answer: Difference in pressure between two points
Explanation
Introduction / Context:Manometers are simple, reliable devices for pressure measurement using hydrostatics. They are widely used in laboratories and field applications for pipes, ducts, and vessels where accurate differential pressure readings are required.
Given Data / Assumptions:
- Static fluids in the manometer legs.
- Known manometric fluid density (e.g., mercury, water).
- Hydrostatic equilibrium; negligible capillary effects in large tubes.
Concept / Approach:
Hydrostatic relation: p2 − p1 = ρ_m * g * Δh (adjusted for densities in each leg as needed). This makes manometers ideal for direct measurement of pressure differences. With one leg open to atmosphere, they measure gauge pressure; with both legs connected, they measure differential pressure between two points.
Step-by-Step Solution:
Set up connections to the two points whose pressure difference is required.Read level difference Δh between manometric fluid columns.Compute Δp using Δp = ρ_m * g * Δh (with appropriate corrections).Verification / Alternative check:
Calibration with known pressure sources confirms the linear relation between Δh and Δp.
Why Other Options Are Wrong:
Atmospheric pressure is usually obtained via barometers; very low pressures often need McLeod or Pirani gauges; velocity is not directly measured by a manometer without additional devices like Pitot-static tubes.
Common Pitfalls:
Ignoring density differences and temperature effects; misreading Δh due to meniscus curvature in narrow tubes.
Final Answer:
Difference in pressure between two points