Vapor and Steam
An introduction to vapor and steam - understanding the properties, states, and characteristics of vapor and steam including saturated vapor, superheated vapor, and steam pressure classifications.
Vapor and Steam
Vapor is a gas - there is no significant physical or chemical difference between a vapor and a gas.
Definition
A vapor is a substance in gaseous state - at a condition where it is ordinarily a liquid or a solid.
The most common example of a vapor is steam - water vaporized during boiling or evaporation.
Key Concepts
Evaporation
Evaporation from a fluid takes place when liquid molecules at the liquid surface have enough momentum to overcome the intermolecular cohesive forces and escape to the atmosphere.
- Increased heat → increased molecular momentum and evaporation
- Increased pressure above a liquid → reduces evaporation
- Reduced pressure above a liquid → increases evaporation
Common Terms
Boiling: Formation of vapor bubbles within a fluid, initiated when absolute pressure reaches vapor pressure.
Saturated Vapor: Vapor at the temperature of the boiling point corresponding to its pressure.
Wet Saturated Vapor: Carries liquid globules in suspension; does not follow the general gas law.
Dry Saturated Vapor: Free from liquid particles; all particles are vaporized.
Super-heated Vapor: Temperature is higher than the boiling point temperature corresponding to the pressure; highly superheated vapors approximate the general gas law.
High Pressure Steam: Steam where pressure greatly exceeds atmospheric pressure.
Low Pressure Steam: Steam where pressure is less than, equal to, or not greatly above atmospheric pressure.