1. What is the Humidity Ratio?

The humidity ratio (also called mixing ratio) is the mass of water vapor per unit mass of dry air. It's a fundamental parameter in psychrometrics and HVAC calculations.

2. How Does the Calculator Work?

The calculator uses the psychrometric formula:

Where:

• \( w \) — Humidity ratio (kg/kg of dry air)
• \( e \) — Vapor pressure (Pa)
• \( P \) — Total pressure (Pa)
• 0.622 — Ratio of molecular weights of water vapor and dry air

Explanation: The formula derives from the ideal gas law and the definition of humidity ratio in terms of partial pressures.

3. Importance of Humidity Ratio

Details: Humidity ratio is essential for air conditioning design, drying processes, and any application where precise control of moisture in air is required.

4. Using the Calculator

Tips: Enter vapor pressure and total pressure in Pascals (Pa). Both values must be positive, and total pressure must be greater than vapor pressure.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between humidity ratio and relative humidity?
A: Humidity ratio is an absolute measure (mass of water per mass of dry air), while relative humidity is a ratio comparing actual vapor pressure to saturation vapor pressure.

Q2: What are typical humidity ratio values?
A: At standard conditions, values range from 0.0001 kg/kg (very dry) to 0.03 kg/kg (very humid).

Q3: How does pressure affect humidity ratio?
A: At higher pressures, the same vapor pressure results in lower humidity ratio, as shown in the denominator (P-e) of the formula.

Q4: Can this be used for non-air gases?
A: The 0.622 constant is specific to air-water vapor mixtures. For other gases, use the appropriate molecular weight ratio.

Q5: How is this related to dew point?
A: Dew point can be calculated from humidity ratio by finding the temperature at which the air would become saturated at that moisture content.