Question

The flow meter which has highest discharge coefficient is ____.

• A. Orifice
• B. Venturi meter
• C. Pivot tube
• D. Rotameter

Hint:

Discharge Coefficients (Cd). Venturi meter: High Cd (~0.98). Flow Nozzle: Medium Cd (~0.95). Orifice Plate: Low Cd (~0.6). Higher Cd generally means lower permanent pressure loss.

Answer 1

The Correct Option is B

The discharge coefficient (Cd) is a measure of how closely an actual flow meter reading matches the theoretical flow rate calculated assuming ideal conditions (e
g
, no energy loss)
A Cd value closer to 1 indicates higher efficiency and lower pressure loss
- Orifice Plate: Has a sharp edge causing significant flow contraction and energy loss, resulting in a low Cd (typically ~0
6)
- Venturi Meter: Features a gradual contraction and a longer, gradual expansion (diffuser) designed to minimize flow separation and recover pressure efficiently
This results in the highest Cd among common differential pressure meters (typically 0
95 to 0
99)
- Pitot Tube: Measures velocity based on stagnation pressure; its accuracy relates more to flow profile and calibration than a single Cd like orifice/venturi
- Rotameter: Variable area meter; its reading depends on float shape, fluid density, and viscosity; not typically compared using Cd in the same way
Therefore, the Venturi meter has the highest discharge coefficient due to its design minimizing irreversible energy losses