CFM Calculator Using Pressure And Diameter

CFM Calculation Formula:

\[ Q = A \times v \]

Where velocity (v) is calculated using Bernoulli's principle:

\[ v = \sqrt{\frac{2 \times \Delta P}{\rho}} \]

Air Flow (CFM):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is a CFM Calculator Using Pressure and Diameter?

Definition: This calculator estimates air flow (CFM) through a duct or pipe based on pressure difference and diameter.

Purpose: It helps HVAC professionals, engineers, and technicians determine air flow rates in ventilation systems.

2. How Does the Calculator Work?

The calculator uses two key formulas:

\[ Q = A \times v \] \[ v = \sqrt{\frac{2 \times \Delta P}{\rho}} \]

Where:

\( Q \) — Air flow (cubic feet per minute, CFM)
\( A \) — Cross-sectional area (square feet)
\( v \) — Air velocity (feet per minute)
\( \Delta P \) — Pressure difference (psi)
\( \rho \) — Air density (slugs/ft³, default 0.002377)

Explanation: Bernoulli's principle calculates velocity from pressure, then multiplied by area to get volume flow rate.

3. Importance of CFM Calculation

Details: Proper CFM estimation ensures adequate ventilation, system efficiency, and compliance with building codes.

4. Using the Calculator

Tips: Enter pressure difference in psi, diameter in inches, and air density (default 0.002377 slugs/ft³ for standard air). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's the typical air density value?
A: Standard air density at sea level is 0.002377 slugs/ft³ (1.225 kg/m³).

Q2: How does diameter affect CFM?
A: CFM increases with the square of diameter - doubling diameter quadruples flow capacity.

Q3: When would I change the air density?
A: Adjust for high altitude (lower density) or different gas mixtures.

Q4: What pressure range is this valid for?
A: Best for moderate pressures (0.1-10 psi). For very high pressures, consider compressibility effects.

Q5: Does this account for friction losses?
A: No, this is theoretical maximum. Real systems will have lower flow due to friction.