Orifice Flow Calculator Formula
Understand the math behind the orifice flow calculator. Each variable explained with a worked example.
Formulas Used
Volumetric Flow Rate
flow_m3s = cd * a_orifice * sqrt(2 * dp_pa / density)Flow Rate
flow_lps = cd * a_orifice * sqrt(2 * dp_pa / density) * 1000Variables
| Variable | Description | Default |
|---|---|---|
cd | Discharge Coefficient (Cd) | 0.62 |
orifice_dia | Orifice Diameter(mm) | 50 |
delta_p | Differential Pressure(kPa) | 20 |
density | Fluid Density(kg/m^3) | 1000 |
d_m | Derived value= orifice_dia / 1000 | calculated |
a_orifice | Derived value= pi * pow(d_m, 2) / 4 | calculated |
dp_pa | Derived value= delta_p * 1000 | calculated |
How It Works
Orifice Plate Flow Measurement
An orifice plate restricts flow in a pipe, creating a measurable pressure difference proportional to flow rate.
Formula
Q = Cd A sqrt(2 delta_P / rho)
where Cd is the discharge coefficient (typically 0.60-0.65 for sharp-edged orifices), A is the orifice area, delta_P is the measured differential pressure, and rho is fluid density.
Worked Example
A 50 mm orifice in a water pipe with 20 kPa differential pressure, Cd = 0.62.
- 01A = pi x 0.05^2 / 4 = 0.001963 m^2
- 02sqrt(2 x 20000 / 1000) = sqrt(40) = 6.325 m/s
- 03Q = 0.62 x 0.001963 x 6.325 = 0.00770 m^3/s = 7.70 L/s
Frequently Asked Questions
What affects the discharge coefficient?
Cd depends on the orifice edge sharpness, the ratio of orifice to pipe diameter (beta ratio), Reynolds number, and upstream flow conditions. Sharp-edged plates typically have Cd = 0.60-0.65.
How is the orifice plate installed?
The plate is clamped between pipe flanges with pressure taps upstream and downstream. Standard tap locations include corner taps, D and D/2 taps, and flange taps, each with slightly different Cd values.
What are the disadvantages of orifice plates?
They cause a permanent pressure loss (typically 40-90% of the measured differential). For applications where energy loss matters, Venturi meters or flow nozzles are more efficient alternatives.
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