Air Flow Rate Calculation Using Pressure

Air Flow Rate Formulas:

\[ V = \sqrt{\frac{2 \times (P_1 - P_2) \times 144}{\rho}} \]
\[ Q = V \times A \times 448.83 \]

Inlet Pressure (P₁):

psi

Outlet Pressure (P₂):

psi

Air Density (ρ):

lb/ft³

Flow Area (A):

ft²

Velocity (V): ft/s

Flow Rate (Q): GPM

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1. What is Air Flow Rate Calculation Using Pressure?

Definition: This calculator determines the air flow rate in GPM (Gallons Per Minute) equivalent based on pressure differential, air density, and flow area.

Purpose: It helps engineers and technicians in HVAC, pneumatic systems, and fluid dynamics to estimate air flow rates.

2. How Does the Calculator Work?

The calculator uses two formulas:

\[ V = \sqrt{\frac{2 \times (P_1 - P_2) \times 144}{\rho}} \]
\[ Q = V \times A \times 448.83 \]

Where:

\( V \) — Velocity (feet per second)
\( P_1 \) — Inlet pressure (psi)
\( P_2 \) — Outlet pressure (psi)
\( \rho \) — Air density (pounds per cubic foot)
\( Q \) — Flow rate (gallons per minute)
\( A \) — Flow area (square feet)

Explanation: First calculates velocity from pressure differential, then converts to volumetric flow rate.

3. Importance of Air Flow Rate Calculation

Details: Accurate flow rate estimation is crucial for system design, efficiency analysis, and equipment sizing in various engineering applications.

4. Using the Calculator

Tips: Enter the pressure values (P₁ must be greater than P₂), air density (default 0.075 lb/ft³ for standard air), and flow area. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: Why multiply by 144 in the velocity formula?
A: This converts psi (pounds per square inch) to psf (pounds per square foot) for consistent units.

Q2: What's the 448.83 factor in the flow rate formula?
A: This converts cubic feet per second to gallons per minute (1 ft³/s = 448.83 GPM).

Q3: What's a typical air density value?
A: Standard air density at sea level is about 0.075 lb/ft³, but varies with altitude and temperature.

Q4: How do I find the flow area?
A: For circular ducts, A = π × (diameter/2)². For rectangular ducts, A = width × height.

Q5: Does this account for friction losses?
A: No, this is an ideal flow calculation. For real-world applications, consider adding a friction loss factor.