What is the basic construction and how is flow estimated in an orifice flow meter?

What is the basic construction and how is flow estimated in an orifice flow meter?

• A. A plate with a restricted opening; flow approximated by Q = C_d A sqrt(2 ΔP / ρ), where C_d is discharge coefficient.
• B. A long pipe with a bend used to measure pressure drop.
• C. A magnetic sensor detecting flow rate.
• D. A turbine wheel placed in the flow and rotated by it.

Answer: (A)

Orifice flow meters use a plate with a restricted opening placed in the flow path. As the fluid passes through the small hole, its velocity increases and it experiences a pressure drop across the plate. The flow rate is estimated from Q = C_d A sqrt(2 ΔP / ρ), where A is the effective area of the opening, ΔP is the pressure difference between upstream and downstream taps, ρ is the fluid density, and C_d is the discharge coefficient that accounts for non-ideal effects like vena contracta and viscosity. You measure the pressure drop with taps near the orifice, know the opening area, and use a calibrated C_d to calculate the volumetric flow. The other options describe different devices: a long pipe bend used to measure pressure drop is a different differential-pressure meter, a magnetic sensor detects flow with electromagnetic principles, and a turbine wheel meter measures flow by rotating blades driven by the flow.

Orifice flow meters use a plate with a restricted opening placed in the flow path. As the fluid passes through the small hole, its velocity increases and it experiences a pressure drop across the plate. The flow rate is estimated from Q = C_d A sqrt(2 ΔP / ρ), where A is the effective area of the opening, ΔP is the pressure difference between upstream and downstream taps, ρ is the fluid density, and C_d is the discharge coefficient that accounts for non-ideal effects like vena contracta and viscosity. You measure the pressure drop with taps near the orifice, know the opening area, and use a calibrated C_d to calculate the volumetric flow.

The other options describe different devices: a long pipe bend used to measure pressure drop is a different differential-pressure meter, a magnetic sensor detects flow with electromagnetic principles, and a turbine wheel meter measures flow by rotating blades driven by the flow.