How To Calculate Vapor Pressure Of Pure Water

Magnus Formula:

\[ e_s = 6.112 \times \exp\left(\frac{17.67 \times T}{T + 243.5}\right) \]

Vapor Pressure (e_s):

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1. What is the Magnus Formula?

The Magnus formula is an empirical relationship that calculates the vapor pressure of pure water over a liquid surface. It's widely used in meteorology and atmospheric sciences to determine saturation vapor pressure at a given temperature.

2. How Does the Calculator Work?

The calculator uses the Magnus formula:

\[ e_s = 6.112 \times \exp\left(\frac{17.67 \times T}{T + 243.5}\right) \]

Where:

\( e_s \) — Saturation vapor pressure (hPa)
\( T \) — Temperature in degrees Celsius (°C)
\( \exp \) — Exponential function

Explanation: The formula provides an accurate estimation of water vapor pressure based on temperature, with coefficients optimized for the temperature range of -50°C to 100°C.

3. Importance of Vapor Pressure Calculation

Details: Vapor pressure calculation is essential for understanding humidity, predicting weather patterns, designing HVAC systems, and various industrial processes involving water evaporation and condensation.

4. Using the Calculator

Tips: Enter temperature in degrees Celsius. The calculator works best for temperatures between -50°C and 100°C, which covers most practical applications.

5. Frequently Asked Questions (FAQ)

Q1: Why use the Magnus formula instead of other equations?
A: The Magnus formula provides a good balance between accuracy and computational simplicity, making it widely adopted in meteorological applications.

Q2: What are typical vapor pressure values?
A: At 0°C, vapor pressure is about 6.11 hPa; at 20°C, it's about 23.39 hPa; and at 100°C, it reaches 1013.25 hPa (standard atmospheric pressure).

Q3: How does vapor pressure relate to relative humidity?
A: Relative humidity = (actual vapor pressure / saturation vapor pressure) × 100%. This calculator provides the saturation vapor pressure.

Q4: Are there limitations to this formula?
A: The formula is most accurate between -40°C and 50°C. For extremely low temperatures or supercooled water, specialized equations may be more appropriate.

Q5: Can this be used for salt water or other liquids?
A: No, this formula is specifically for pure water. Salt water and other liquids have different vapor pressure characteristics.