Share:
How It Works
The orifice equation Q = Cd × A × √(2gH) calculates flow through a sharp-edged opening under gravity. The discharge coefficient (Cd) accounts for real-world losses from friction and flow contraction (vena contracta). Sharp-edged orifices typically have Cd ≈ 0.62; rounded entrances reach 0.95–0.99.
Example Problem
A sharp-edged orifice (Cd = 0.62) has a diameter of 50 mm and a head of 3 m. What is the flow rate?
- Area: A = π/4 × 0.05² = 0.001963 m²
- Q = 0.62 × 0.001963 × √(2 × 9.81 × 3)
- Q = 0.001217 × 7.672 = 0.00934 m³/s (9.3 L/s)
Frequently Asked Questions
What is the discharge coefficient for an orifice?
Cd accounts for energy losses as fluid passes through the opening. A sharp-edged orifice has Cd ≈ 0.61–0.65. Well-rounded entrances approach 0.95–0.99.
What is the difference between an orifice and a nozzle?
An orifice is a thin plate with a hole; a nozzle has a converging profile that guides flow smoothly. Nozzles have higher discharge coefficients (0.95+) because they reduce turbulence and flow separation.
How is orifice flow used for flow measurement?
Orifice plates installed in pipelines create a measurable pressure drop proportional to flow rate squared. By measuring the differential pressure, engineers can accurately determine the flow rate using a calibrated Cd.
Related Calculators
- Venturi Meter Calculator — a low-loss alternative to orifice plates for flow measurement.
- Bernoulli Theorem Calculator — the energy principle behind the orifice equation.
- Fluid Pressure Calculator — calculate hydrostatic head driving orifice flow.
- Continuity Equation Calculator — relate flow rate, area, and velocity at the orifice.
- Reynolds Number Calculator — determine the flow regime affecting the discharge coefficient.
- Pressure Unit Converter — convert between head and pressure units for orifice calculations.