Formula Used
Incompressible velocity uses pressure difference and fluid density. Compressible analysis uses total-to-static pressure ratios. Corrections improve practical accuracy across measured operating conditions today.
| Purpose | Formula |
|---|---|
| Incompressible velocity | v = Cp √(2ΔP/ρ) |
| Dynamic pressure | q = ρv²/2 |
| Subsonic Mach | M = √[(2/(γ−1))((Pt/Ps)(γ−1)/γ−1)] |
| Volumetric flow | Q = Av |
| Mass flow | ṁ = ρQ |
How To Use
Select the required calculation mode first. Enter pressure, fluid, temperature, and correction values. Review warnings before using results for important engineering decisions.
Enable atmospheric modelling for altitude-sensitive gas calculations. Add duct dimensions for volumetric and mass flow. Export the completed results using the available report buttons.
Worked Example Data
This example uses air at standard sea-level conditions. The probe measures one hundred twenty-five pascals differential pressure. The resulting speed supports a practical ventilation assessment process.
| Input | Example value | Unit |
|---|---|---|
| Differential pressure | 125 | Pa |
| Air density | 1.225 | kg/m³ |
| Pitot coefficient | 1.00 | — |
| Temperature | 15 | °C |
| Static pressure | 101325 | Pa |
Assumptions And Limitations
The probe should face the local flow direction. Steady flow provides the most reliable pressure reading. Professional verification remains essential for critical engineering applications today.
Supersonic calculations use the Rayleigh Pitot relationship. Strong shocks and turbulence can increase measurement uncertainty. Confirm instrument limits before testing hazardous operating environments safely.
Frequently Asked Questions
What does a Pitot tube measure?
A Pitot tube measures total pressure directly. Static ports provide the surrounding fluid pressure. Their difference represents dynamic pressure for reliable velocity calculations.
When should compressible flow be enabled?
Enable compressibility near Mach zero point three. Density changes then affect pressure-based velocity estimates. Compressible equations improve results as measured Mach number increases.
Why does fluid density matter?
Velocity depends inversely on the square root of density. Incorrect density creates a systematic speed error. Temperature and pressure often change gas density quite significantly.
What is the Pitot coefficient?
The coefficient represents probe calibration and geometry effects. Ideal probes commonly use a value near one. Manufacturer calibration data should guide final coefficient value selection.
How does probe angle affect results?
Misalignment reduces pressure captured by the probe opening. Larger angles can create substantial velocity errors. Align the probe carefully with the local airflow direction.
Can this calculator handle liquids?
Yes, incompressible equations support water and common liquids. Enter accurate density and viscosity values. Avoid compressible settings for ordinary low-speed liquid flow measurements.
How is duct flow calculated?
The calculator multiplies average velocity by duct area. A profile factor adjusts nonuniform traverse measurements. Mass flow multiplies volume flow by measured fluid density.
What causes negative differential pressure?
Reversed tubing can produce negative differential readings. Blocked ports or offsets may cause similar behaviour. Inspect connections before accepting any negative differential measurement result.
Are the results suitable for certification?
The calculator supports analysis and preliminary engineering checks. Certification requires calibrated instruments and approved procedures. Follow governing standards and qualified professional review requirements carefully.