Air Flow Rate Through an Orifice

Air Flow Rate Formula:

\[ Q = C_d \times A \times \sqrt{\frac{2 \times \Delta P}{\rho_{air}}} \times 448.83 \]

Discharge Coefficient (C_d):

Orifice Area (A):

ft²

Pressure Difference (ΔP):

psi

Air Density (ρ_air):

lb/ft³

Air Flow Rate (Q): GPM equivalent

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1. What is Air Flow Rate Through an Orifice?

Definition: This calculator estimates the volumetric flow rate of air through an orifice, expressed in gallons per minute (GPM) equivalent.

Purpose: It helps engineers and technicians determine airflow in ventilation systems, pneumatic controls, and other air handling applications.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ Q = C_d \times A \times \sqrt{\frac{2 \times \Delta P}{\rho_{air}}} \times 448.83 \]

Where:

\( Q \) — Air flow rate (GPM equivalent)
\( C_d \) — Discharge coefficient (dimensionless)
\( A \) — Orifice area (ft²)
\( \Delta P \) — Pressure difference across orifice (psi)
\( \rho_{air} \) — Air density (lb/ft³)

Explanation: The formula calculates the theoretical flow rate adjusted by the discharge coefficient and converted to GPM equivalent.

3. Importance of Air Flow Calculation

Details: Accurate airflow measurement is critical for system design, performance evaluation, and troubleshooting in HVAC and industrial applications.

4. Using the Calculator

Tips: Enter the discharge coefficient (default 0.62 for sharp-edged orifice), orifice area, pressure difference, and air density (default 0.075 lb/ft³). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical discharge coefficient (C_d)?
A: For sharp-edged orifices, ~0.62; for rounded orifices, up to 0.98. Consult engineering references for specific geometries.

Q2: Why is the result in GPM equivalent?
A: The conversion factor 448.83 converts the result to gallons per minute for easier comparison with liquid flow rates.

Q3: How does air density affect the calculation?
A: Higher density (colder air or higher pressure) reduces flow rate for the same pressure difference.

Q4: What's the range of validity for this formula?
A: It works well for subsonic flow (pressure ratios < 0.528) and turbulent flow conditions.

Q5: How do I calculate orifice area for a circular opening?
A: Use \( A = \pi \times (diameter/2)^2 \) with diameter in feet.