1. What is Vapour Pressure of Water?

Definition: Vapour pressure is the pressure exerted by water vapor in thermodynamic equilibrium with its condensed phases at a given temperature.

Purpose: This calculator helps determine the saturation vapour pressure of water at a specific temperature, important for meteorology, HVAC design, and industrial processes.

2. How Does the Calculator Work?

The calculator uses the Magnus formula:

Where:

• \( P \) — Vapour pressure (hPa)
• \( T \) — Temperature (°C)
• \( e \) — Euler's number (~2.71828)

Explanation: This empirical formula approximates the relationship between temperature and the saturation vapour pressure of water.

3. Importance of Vapour Pressure Calculation

Details: Understanding vapour pressure is crucial for weather forecasting, humidity control, drying processes, and many industrial applications.

4. Using the Calculator

Tips: Simply enter the temperature in Celsius. The calculator works for temperatures above absolute zero (-273.15°C).

5. Frequently Asked Questions (FAQ)

Q1: What units does this calculator use?
A: Temperature in Celsius (°C) and vapour pressure in hectopascals (hPa).

Q2: How accurate is this formula?
A: The Magnus formula is accurate to within 0.1% for temperatures between -30°C and 35°C.

Q3: What's the vapour pressure at 100°C?
A: At boiling point (100°C at sea level), vapour pressure equals atmospheric pressure (1013.25 hPa).

Q4: Can I use this for ice/sublimation?
A: No, this formula is for liquid water. Different equations exist for ice.

Q5: How does altitude affect vapour pressure?
A: Vapour pressure depends only on temperature, but boiling point changes with pressure.