Calculation Results
Results use absolute temperature and pressure values.
Formula substitution
Step-by-step calculation
Temperature comparison table
| Temperature | Dynamic viscosity | Density | Kinematic viscosity |
|---|
Calculation History
| Date | Mode | Temperature | Pressure | Kinematic viscosity |
|---|
Formula Used
Kinematic viscosity equals dynamic viscosity divided by fluid density. Temperature changes both values through separate physical relationships. The calculator combines those relationships for consistent engineering estimates.
Sutherland’s law estimates dynamic viscosity for dilute gases. Humid-air density uses dry and vapour partial pressures. Custom mode supports alternative constants for specialised gas studies.
How to Use the Calculator
Select the calculation mode matching your available measurements. Enter temperature, pressure, altitude, or known fluid properties. Then review units before starting the final calculation process.
Choose a preset for common atmospheric operating conditions. Advanced inputs provide Reynolds and thermal diffusivity estimates. Export buttons save results for reports and comparisons later.
Example Data
| Condition | Temperature | Pressure | Humidity | Approximate ν |
|---|---|---|---|---|
| Cold dry air | 0°C | 101.325 kPa | 0% | 1.33 × 10⁻⁵ m²/s |
| Standard indoor air | 20°C | 101.325 kPa | 50% | 1.51 × 10⁻⁵ m²/s |
| Warm humid air | 35°C | 101.325 kPa | 80% | 1.69 × 10⁻⁵ m²/s |
Assumptions and Limitations
The default model treats air as an ideal mixture. Sutherland’s law suits ordinary engineering temperature ranges. Extreme pressures require real-gas data and validated property models.
Altitude pressure follows a simplified standard-atmosphere relationship. Reynolds classifications assume familiar internal-flow threshold conventions. Always verify safety-critical work using authoritative design standards first.
Frequently Asked Questions
What is kinematic viscosity?
Kinematic viscosity measures momentum diffusion relative to fluid density. Its SI unit is square metres per second. Larger values indicate faster momentum spreading through moving air.
How does temperature affect air viscosity?
Dynamic viscosity generally increases as air temperature rises. Density usually decreases when pressure remains unchanged. Together, these effects increase kinematic viscosity with temperature significantly.
How does pressure affect kinematic viscosity?
Moderate pressure changes barely alter dilute-gas dynamic viscosity. Higher pressure increases density at constant temperature. Therefore, kinematic viscosity normally decreases as pressure rises steadily.
Does humidity change the result?
Humidity slightly changes air density and mixture behaviour. Water vapour is lighter than typical dry air. Humid air therefore shows slightly higher kinematic viscosity values.
Why must pressure be absolute?
Gas density equations require pressure measured from vacuum. Gauge pressure excludes the surrounding atmospheric pressure contribution. Add atmospheric pressure before using any gauge measurement here.
What does Sutherland’s law calculate?
Sutherland’s law estimates gas dynamic viscosity from temperature. It uses a reference viscosity and temperature constant. The model remains practical across common air engineering ranges.
What is the difference between cSt and St?
Stokes and centistokes are kinematic viscosity measurement units. One Stokes equals one square centimetre per second. One centistoke equals one square millimetre per second exactly.
Can this calculator estimate Reynolds number?
Yes, enter flow velocity and characteristic length values. Reynolds number equals velocity times length divided by viscosity. Its classification depends on geometry and operating conditions chosen.
When should custom gas mode be used?
Use custom mode for gases with known property constants. Enter validated Sutherland and specific gas constant values. Confirm those constants match your intended temperature range carefully.