CFM to Mass Flow Rate Calculator

Mass Flow Rate Formula:

\[ W = Q_{cfm} \times \rho_{air} \times 60 \]

Mass Flow Rate (W): lb/hr

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1. What is a CFM to Mass Flow Rate Calculator?

Definition: This calculator converts volumetric air flow (CFM) to mass flow rate (lb/hr) using air density.

Purpose: It helps HVAC engineers, mechanical designers, and technicians determine the mass flow of air in systems.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ W = Q_{cfm} \times \rho_{air} \times 60 \]

Where:

\( W \) — Mass flow rate (pounds per hour)
\( Q_{cfm} \) — Volumetric flow rate (cubic feet per minute)
\( \rho_{air} \) — Air density (pounds per cubic foot)
60 — Conversion factor (minutes to hours)

Explanation: The CFM is multiplied by air density to get mass per minute, then multiplied by 60 to convert to hourly rate.

3. Importance of Mass Flow Rate Calculation

Details: Mass flow rate is critical for HVAC system design, combustion calculations, and process engineering where precise air measurements are needed.

4. Using the Calculator

Tips: Enter the CFM value and air density (default 0.075 lb/ft³ for standard air). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is standard air density?
A: Standard air density is 0.075 lb/ft³ at 70°F and sea level pressure (29.92 in Hg).

Q2: When should I adjust the air density value?
A: Adjust for altitude, temperature, or humidity differences. Higher altitudes or temperatures reduce air density.

Q3: Why convert CFM to mass flow rate?
A: Mass flow rate remains constant regardless of temperature/pressure changes, making it more reliable for calculations.

Q4: How does this relate to HVAC systems?
A: Mass flow rate is essential for calculating heating/cooling loads and proper system sizing.

Q5: What's the conversion factor for SI units?
A: For kg/hr from m³/s, use ρ_air (~1.2 kg/m³) and multiply by 3600 (seconds to hours).