Orifice Flow Rate Calculator
Calculate Volumetric & Mass Flow for Liquids and Gases
Incompressible (Liquid)
Compressible (Gas – Simple)
Beta Ratio (β):
0
Velocity of Approach Factor:
0
Volumetric Flow (Q) – m³/h:
0
Mass Flow Rate (ṁ) – kg/s:
0
Understanding Orifice Flow Measurement
An orifice plate is a device used for measuring the flow rate of a fluid. It works on the principle of Bernoulli's theorem, which states that there is a relationship between the pressure of the fluid and the velocity of the fluid. When a fluid passes through a restriction (the orifice), its velocity increases and its pressure decreases.
Q = Cd * A₂ * sqrt( (2 * ΔP) / (ρ * (1 – β⁴)) )
Key Parameters Defined
- Orifice Diameter (d): The internal diameter of the hole in the plate.
- Pipe Diameter (D): The internal diameter of the inlet pipe.
- Beta Ratio (β): The ratio of the orifice diameter to the pipe diameter (d/D). This should typically be between 0.3 and 0.7 for accuracy.
- Discharge Coefficient (Cd): A factor that accounts for energy losses and the contraction of the fluid jet (vena contracta). For sharp-edged orifices, it is often around 0.6 to 0.65.
- Pressure Drop (ΔP): The difference in pressure measured before and after the orifice plate.
- Fluid Density (ρ): The mass per unit volume of the fluid at operating conditions.
Application and Limitations
Orifice meters are widely used in the oil and gas industry, water treatment, and chemical processing because they are simple, inexpensive, and have no moving parts. However, they do cause a permanent pressure loss in the system. For compressible fluids (gases), an expansion factor (Y) must often be applied if the pressure drop is significant relative to the absolute upstream pressure.
Practical Example
If you have water (density ~1000 kg/m³) flowing through a 100mm pipe with a 50mm orifice, and the measured pressure drop is 5,000 Pascals, assuming a discharge coefficient of 0.61:
- The Beta Ratio is 0.5 (50/100).
- The cross-sectional area of the orifice is approximately 0.00196 m².
- The resulting flow rate would be approximately 13.9 m³/h.