1. What is Partial Pressure of Water Vapor?

Definition: This calculator determines the partial pressure of water vapor in air based on saturation pressure and relative humidity.

Purpose: It's essential for meteorology, HVAC design, chemical engineering, and understanding atmospheric conditions.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( P_w \) — Partial pressure of water vapor (Pa)
• \( P \) — Saturation vapor pressure (Pa)
• \( RH \) — Relative humidity (decimal from 0 to 1)

Explanation: The saturation pressure (maximum possible water vapor pressure at a given temperature) is multiplied by the relative humidity (how saturated the air actually is) to get the actual water vapor pressure.

3. Importance of Partial Pressure Calculation

Details: Knowing water vapor partial pressure is crucial for predicting condensation, calculating dew point, designing drying processes, and understanding human comfort in buildings.

4. Using the Calculator

Tips: Enter the saturation pressure in Pascals and relative humidity as a decimal between 0 (0%) and 1 (100%). The saturation pressure can be found from temperature using the Antoine equation or vapor pressure tables.

5. Frequently Asked Questions (FAQ)

Q1: What is saturation vapor pressure?
A: The maximum pressure of water vapor that can exist in equilibrium with liquid water at a given temperature.

Q2: How do I find saturation pressure?
A: Use our Saturation Pressure Calculator or consult standard vapor pressure tables based on temperature.

Q3: Why use decimal for relative humidity?
A: Calculations require values between 0-1. Multiply percentage values by 0.01 to convert (e.g., 50% = 0.5).

Q4: What are typical values for P_w?
A: At room temperature (20°C), P ≈ 2339 Pa, so at 50% RH, P_w ≈ 1170 Pa.

Q5: How does altitude affect this calculation?
A: The formula remains valid, but total atmospheric pressure decreases with altitude, affecting absolute humidity measurements.