How to Calculate Air Flow Rate From Pressure

Orifice Flow Equation:

\[ Q = C \times \sqrt{\frac{\Delta P}{\rho}} \]

Flow Rate (Q):

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1. What is the Orifice Flow Equation?

The orifice flow equation calculates the volumetric flow rate of a fluid through an orifice based on pressure drop and fluid properties. It is commonly used in fluid dynamics, HVAC systems, and industrial process control for air and gas flow measurements.

2. How Does the Calculator Work?

The calculator uses the orifice flow equation:

\[ Q = C \times \sqrt{\frac{\Delta P}{\rho}} \]

Where:

\( Q \) — Volumetric flow rate (m³/s)
\( C \) — Discharge coefficient (dimensionless)
\( \Delta P \) — Pressure drop across orifice (Pa)
\( \rho \) — Fluid density (kg/m³)

Explanation: The equation relates flow rate to the square root of pressure drop, following Bernoulli's principle for incompressible flow through a restriction.

3. Importance of Flow Rate Calculation

Details: Accurate flow rate calculation is essential for system design, performance monitoring, energy efficiency optimization, and ensuring proper operation of ventilation, pneumatic, and process systems.

4. Using the Calculator

Tips: Enter discharge coefficient (typically 0.6-0.9 for sharp-edged orifices), pressure drop in Pascals, and fluid density in kg/m³. All values must be positive and non-zero.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical discharge coefficient value?
A: For sharp-edged orifices, C is typically 0.6-0.65. For well-designed nozzles, it can be 0.95-0.99. The exact value depends on orifice geometry and Reynolds number.

Q2: Can this equation be used for liquids?
A: Yes, the equation works for both gases and liquids, provided the flow is incompressible and turbulent.

Q3: What is standard air density?
A: At sea level and 20°C, standard air density is approximately 1.204 kg/m³. Density varies with temperature, pressure, and humidity.

Q4: Are there limitations to this equation?
A: The equation assumes incompressible flow, which is valid for air at low velocities (Mach number < 0.3). For high-pressure drops, compressibility effects must be considered.

Q5: How accurate is orifice flow measurement?
A: With proper calibration and installation, orifice flow meters can achieve ±1-2% accuracy under ideal conditions, though typical industrial accuracy is ±2-5%.