Air Pressure Flow Rate Calculator
Calculation Results
Understanding Air Pressure Flow Rate
Calculating the flow rate of air through an orifice, nozzle, or pipe is a fundamental task in pneumatic engineering, HVAC system design, and fluid dynamics. This calculator estimates the volumetric flow rate based on the pressure differential across an opening, the size of that opening, and the properties of the air itself.
The flow of air is driven by a pressure gradient; air moves from areas of high pressure to areas of low pressure. The magnitude of this flow is determined by how large the opening is and how great the pressure difference is, governed largely by Bernoulli's principle.
The Flow Rate Formula
This calculator utilizes the standard orifice flow equation for incompressible flow (a reasonable approximation for low pressure differentials):
Q = Cd × A × √( (2 × ΔP) / ρ )
- Q: Volumetric Flow Rate (m³/s)
- Cd: Discharge Coefficient (dimensionless efficiency factor)
- A: Cross-sectional Area of the opening (m²)
- ΔP: Pressure Differential (Pascals)
- ρ (rho): Air Density (kg/m³)
Key Input Parameters Explained
- Diameter (mm): The physical diameter of the hole, pipe, or orifice through which the air is escaping or flowing. A larger diameter results in a significantly higher flow rate because the area increases with the square of the diameter.
- Pressure Differential (Pa): This is the drop in pressure across the orifice. For example, if a tank is at 101,000 Pa and the outside air is 100,000 Pa, the differential is 1,000 Pa. Higher pressure drops create higher velocities.
- Discharge Coefficient (Cd): In the real world, friction and turbulence reduce flow. A sharp-edged orifice typically has a Cd of around 0.60 to 0.62. A smooth, rounded nozzle may have a Cd closer to 0.98.
- Air Density (kg/m³): Air density changes with temperature and altitude. Standard sea-level air density is approximately 1.225 kg/m³. If the air is compressed or heated, this value should be adjusted for accuracy.
Example Calculation
Imagine you have a ventilation duct with a sharp-edged orifice plate.
- Orifice Diameter: 50 mm
- Pressure Difference: 250 Pa
- Air Density: 1.225 kg/m³
- Discharge Coefficient: 0.61
First, convert the diameter to meters (0.05 m) and calculate the Area (A ≈ 0.00196 m²).
Then, calculate the velocity term: √( (2 * 250) / 1.225 ) ≈ 20.2 m/s.
Finally, multiply by Area and Cd: 0.61 * 0.00196 * 20.2 ≈ 0.024 m³/s.
Why is this important?
HVAC Systems: Technicians use these calculations to balance air ducts, ensuring every room gets the correct amount of fresh air or cooling.
Pneumatics: In manufacturing, knowing the flow rate helps in selecting the right size valves and hoses to operate cylinders and actuators efficiently.
Leak Detection: By measuring the pressure drop across a known leak size, engineers can estimate how much air is being lost in a compressed air system, which directly correlates to energy costs.