on . Posted in Fluid Dynamics

matter phasesIn physics and chemistry, vapor is a gaseous state of matter that exists at or below its critical temperature and pressure.  It is a gas that is generated from a liquid or a solid by heating or by reducing the pressure on the substance, causing its molecules to escape into the air.

The term "vapor" is often used interchangeably with "gas", but it specifically refers to the gaseous form of a substance that is normally a liquid or solid at standard temperature and pressure.  Examples of vapor include water vapor (the gaseous form of water), steam (the gaseous form of water that has been heated to its boiling point), and gasoline vapor (the gaseous form of gasoline).

Vapor can be produced through various processes such as evaporation, boiling, sublimation, and vaporization.  The behavior of vapor is influenced by various factors such as temperature, pressure, and the presence of other substances in the surrounding environment.  Vapor is important in many fields such as meteorology, where water vapor plays a significant role in weather patterns and the formation of clouds and precipitation.  It is also important in many industrial processes such as distillation, where the separation of different substances is achieved through their different boiling points and vapor pressures.

Vapor Types

  • Evaporation  -  The condition that occurs when heat is absorbed by the surface of a liquid and it changes to vapor.
  • Liquid Vapor Mixture  -  Liquid vapor mixture (called a two-phase) of the same substance can coexist at the same pressure and temperature.
  • Saturated Vapor  -  Saturated vapor is a vapor at a temperature of the boiling point on the verge of condensing.
  • Superheated Vapor  -  Superheated vapor is when vapor has absorbed more heat than is needed to vaporize.  It will not condense when small amounts of heat is removed.

Vapor Quality

The mass friction of a vapor in a liquid vapor mixture in a two-phase liquid vapor regoin is called vapor quality, also called dryness fraction.


 Vapor Quality formula

\( x = m_{vapor} \;/\; m_{liquid}  + m_{vapor}  \) 

\( x  <  1 \; \rightarrow \)     (wet steam)

\( x  >  1 \; \rightarrow \)     (dry steam)

Symbol English Metric
\( x \) = steam quality   \(dimensionless\)
\( m_{liquid} \) = mass of liquid \(lbm\) \(kg\)
\( m_{vapor} \) = mass of vapor \(lbm\) \(kg\)


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Tags: Steam Gas Vapor