Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

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Vapor is the gas state of a liquid or solid.  Both vapor and gas are basically the same thing.  Gas just happens to be the term normally used.

Actual Vapor Pressure

Actual Vapor Pressure formula

\(\large{ e =  \frac  { RH   e_s   }  { 100 }  }\)         


\(\large{ e }\) = actual vapor pressure

\(\large{ RH }\) = relative humidity

\(\large{ e_s }\) = saturated vapor pressure

Casing Vapor Recovery

The main objectives of a casing vapor recovery system are to

  • Minimize back pressure on wells
  • Minimize discharge of hydrocarbons and other fugitive gasses to the environment
  • Recovery of heat from casing gasses
  • Collect hydrocarbon condensate in the gas streams for addition to the sales stream.

In oil fields that are on steam-flood or steam lift, there is an overt effort to maintain a low back pressure on the producing formation. This is done by keeping the wells "pumped off" and by lowering the pressure in the annulus.

In a system that has steam injected, steam vapor often times will come up through the annulus and will condense in the CVR system.


A CVR System consists of:

  • collection branch and trunk lines
  • Heat exchangers or condensers
  • Vapor-Liquid Separators
  • Water / Oil Separation
  • Incineration of non-condensible gasses

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.

Saturated Vapor Pressure

Saturated vapor pressure ( \(e_s\) ) is the pressure applied by air that is mixed with water vapor, at a given temperature, at its maximum saturation point.

Saturated Vapor Pressure formula

\(\large{ e_s = 100 \frac{RH}{e}  }\)         


\(\large{ e_s }\) = saturated vapor pressure

\(\large{ RH }\) = relative humidity

\(\large{ e }\) = actual vapor pressure

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 Density of Gas

Vapor Density of Gas Formula

\(\large{ G_{vd} = \frac {G}{H} }\)         


\(\large{ G_{vd} }\) = vapor density of gas

\(\large{ G }\) = density of the gas

\(\large{ H }\) = density of hydrogen

Vapor Pressure

Vapor pressure ( \(p_v\) ) of a substance is the pressure at a certain temperature when the liquid and vapor are in equilibrium.  Liquid vapor pressure is measured in the laboratory at 100 degrees fahrenheit and is referred to as the Reed Vapor Pressure.   As the temperature of a liquid increases, the vapor pressure also increases.   

Boiling point is the temperature at which the vapor pressure equals atmospheric pressure.  In engineering, the vapor pressure is extremely important when sizing pumps.  When there is low net positive suction head available \(NPSHa\), vapor pressure can play a large role in preventing (or assisting in) cavitation.

Vapor Pressure Formula

\(\large{ p_s = x_s   p_{s}{^o} }\)        


\(\large{ p_s }\) = vapor pressure of the solution

\(\large{ x_s }\) = mole fraction of the solvent

\(\large{ p_{s}{^o} }\) = vapor pressure of pure solvent

Water Vapor Diffusion

The process by which water vapor spreads or moves through permeable materials caused by a difference in water vapor pressure.

Water Vapor Pressure

The pressure of water vapor at a given temperature; also the component of atmospheric pressure contributed by the presence of water vapor.

Water Vapor Pressure formula

\(\large{ p =  10^{\; A -  \frac  { B }   {  C \;+\; T  } }  }\)         


\(\large{ p }\) = vapor pressure of water

\(\large{ A }\) = Antoine constant for water

\(\large{ B }\) = Antoine constant for water

\(\large{ C }\) = Antoine constant for water

\(\large{ T }\) = water temperature

Antoine Constants for Water

Water TemperatureABC
1 to 100 degrees celsius 8.07131 1730.63 233.426
99 to 374 degrees celsius 8.14019 1810.94 244.485



Tags: Equations for Steam