What is Dew Point?
Dew Point is the temperature at which a gas (such as air) becomes saturated with water vapour, causing condensation to form. In simple terms, when air cools to this point, water vapour condenses into liquid water, forming dew.
Cooling the air at constant pressure decreases its capacity to hold water vapour. When it reaches the dew point temperature, any further cooling results in water condensing out of the air as liquid (or frost if below 0 °C).
Key Concepts
- Higher dew point = more moisture in the air
- Lower dew point = drier air
- Dew point is independent of air temperature; it reflects the absolute moisture content.
Dewpoint Vs Humidity
It is important to distinguish dew point from relative humidity (RH):
| Parameter | Meaning | Dependence |
|---|---|---|
| Dew Point | Absolute moisture content | Independent of temperature |
| Relative Humidity | % of moisture relative to capacity | Strongly temperature-dependent |
For trace moisture measurement in compressed air and industrial processes, dew point is preferred because it stays consistent and gives a direct indication of how much water vapour is present, which is especially important when dealing with trace levels.
Dew Point in Compressed Air Systems
In compressed air systems, the concept extends to Pressure Dew Point (PDP). This is the dew point temperature at the operating pressure of the system, rather than at atmospheric pressure. Pressure can affect dew point by influencing the air’s capacity to hold water vapour.
When air is compressed, pressure increases, volume decreases and water vapour becomes more concentrated. This means that even if the actual moisture content has not changed, the dew point at pressure is higher than at atmospheric conditions.
Key Takeaway
In process gases and compressed air systems, dew point is the most reliable and practical parameter for measuring and controlling trace moisture, ensuring system reliability, product quality and operational safety.
To learn more about dewpoint measurement for your gas or compressed air system, contact the team below.
Portable Hygrometers
Inline Analyzers
