Enter Input Data
Example Data Table
| Scenario | ΔP | Density | Cd | β | Diameter | Estimated Velocity |
|---|---|---|---|---|---|---|
| Air duct test | 250 Pa | 1.225 kg/m³ | 1.00 | 0.00 | 0.30 m | 20.203 m/s |
| Water line | 15 kPa | 998 kg/m³ | 0.98 | 0.25 | 0.10 m | 5.392 m/s |
| Orifice-based gas check | 2.8 inH2O | 1.18 kg/m³ | 0.97 | 0.55 | 0.20 m | 35.073 m/s |
Formula Used
Ideal velocity from differential pressure:
v_ideal = √(2ΔP / ρ)
Corrected velocity with discharge coefficient and beta ratio:
v = Cd × √(2ΔP / (ρ(1 - β⁴)))
Area of the flow section:
A = πD² / 4
Volumetric flow rate:
Q = vA
Reynolds number:
Re = ρvD / μ
Here, ΔP is differential pressure, ρ is fluid density, Cd is discharge coefficient, β is diameter ratio for constricted devices, D is pipe diameter, and μ is dynamic viscosity.
How to Use This Calculator
- Enter the measured differential pressure and choose its unit.
- Provide the fluid density and choose the matching density unit.
- Set the discharge coefficient. Use 1.0 for an ideal estimate.
- Enter beta ratio if a constriction device affects the reading.
- Supply pipe diameter to estimate section area and volumetric flow.
- Enter dynamic viscosity to compute Reynolds number.
- Select the desired output velocity unit.
- Click the calculate button to show results above the form.
- Use the CSV or PDF buttons to export the result summary.
Frequently Asked Questions
1) What does differential pressure mean here?
It is the pressure difference between two points in a moving fluid. That difference represents kinetic energy change and can be converted into velocity using Bernoulli-based relations.
2) When should I use a beta ratio?
Use beta ratio when pressure is measured across a constriction, such as an orifice or Venturi section. Set beta to zero for a simple pressure-to-velocity estimate.
3) Why is density so important?
For the same pressure difference, lighter fluids accelerate more and produce higher velocity. Denser fluids need more pressure to reach the same speed.
4) What discharge coefficient should I enter?
Enter a tested or design value for your sensor or geometry. Use 1.0 only when you want an idealized result without empirical correction.
5) Does this work for gases and liquids?
Yes. It works for both, provided density is known. For highly compressible gas flow at larger pressure ratios, a compressible-flow method may be more suitable.
6) What is Reynolds number used for?
Reynolds number helps classify the flow regime. It indicates whether viscous or inertial effects dominate and supports better interpretation of sensor corrections.
7) Why does the chart change with pressure?
Velocity varies with the square root of differential pressure. The graph shows that relationship around your current conditions, making sensitivity easier to inspect.
8) Can I use this for duct balancing?
Yes. It can help estimate air speed from measured pressure difference, especially during duct testing, balancing, commissioning, or field diagnostics.