Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

This is an AMP page - Open full page! for all features.

Vapor and Steam

Sponsored Links

Vapor is a gas - there is no significant physical or chemical difference between a vapor and a gas.

  • 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 vaporation. The water vapor in the atmosphere is invisible and is often called moist. Knowledge about moist in air is important for the design of air-condition applications - like HVAC systems and industrial dryers. Moist air technology is often called Air Psychrometrics.

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. When heat is added to a liquid the molecular momentum and the evaporation of the liquid is increased. A reduction of the pressure above a liquid reduces the momentum needed for molecules to escape and evaporation is increased.

  • increased pressure above a liquid - reduces evaporation

This can be observed as lower water boiling temperature at higher altitudes.

Common terms in connection with vapor and steam:


  • Boiling is the formation of vapor bubbles within a fluid. Boiling is initiated when the absolute pressure in a fluid reaches vapor pressure.

Saturated Vapor

Wet Saturated Vapor

  • A wet saturated vapor carries liquid globules in suspension. A wet saturated vapor is a substance in the gaseous state which does not follow the general gas law.

Dry Saturated Vapor

  • A dry saturated vapor is free from liquid particles. All particles are vaporized - any decrease in vapor temperature or increase in vapor pressure, condensates liquid particles in the vapor. A dry saturated vapor is a substance in the gaseous state which does not follow the general gas law.

Super-heated Vapor

  • In super-heated vapor the temperature is higher than the boiling point temperature corresponding to the pressure. The superheated vapor can not exist in contact with the fluid, nor contain fluid particles. An increase in the pressure or decrease in the temperature will not - within limits - condensate out liquid particles in the vapor. Highly superheated vapors are gases that approximately follow the general gas law.

High Pressure Steam

  • Steam where the pressure greatly exceeds the atmosphere pressure.

Low Pressure Steam

  • Steam of which the pressure is less than, equal to, or not greatly above, atmospheric pressure.
Sponsored Links

Related Topics

Flash Steam

Generation of flash steam in steam and condensate systems. Thermodynamic fundamentals, heat loss, energy recovery and more.

Gases and Compressed Air

Properties of air, LNG, LPG and other common gases. Pipeline capacities and sizing of relief valves.

Steam and Condensate

Design of steam & condensate systems with properties, capacities, sizing of pipe lines, system configuration and more.


Calculate heat, work, temperature and energy. The thermodynamics of steam and condensate systems. Water and Ice properties.

Related Documents

Air - Humidifying by Adding Steam or Water

Air can be humidified by adding water or steam.

Air - Humidifying with Steam - Imperial Units

Estimate the amount of steam required (lb/h in 100 cfm) in humid air.

Air and Steam Mixtures

Air in the steam will lower the surface temperatures in heat exchangers - and less heat will be transferred.

Condensate Pipes - Flash Steam Generated

Calculate flash steam generation in condensate pipe lines.

Flash Steam Generation - SI-units

When condensate leaves the steam traps - flash steam is generated. Amount of flash steam generated at different pressures - kN/m2.

Molecular Weight of Substances

Definition and molecular weight (molar mass) of some common substances.

Non-ideal gas - Van der Waal's Equation and Constants

The van der Waals constants for more than 200 gases used to correct for non-ideal behavior of gases caused by intermolecular forces and the volume occupied by the gas particles.

Properties of Saturated Steam - SI Units

Saturated Steam Table with steam properties as specific volume, density, specific enthalpy and specific entropy.

Saturated Steam - Properties - Imperial Units

Steam table with sensible, latent and total heat, and specific volume at different gauge pressures and temperatures.

Steam and Vapor Enthalpy

Vapor and steam enthalpy, specific enthalpy of saturated liquid, saturated vapor and superheated vapor.

Steam Flash Generation (bar)

The amount of flash steam generated depends on steam pressure and pressure in the condensate lines.

Superheated Steam - Entropy

The entropy of steam superheated to temperatures above saturation points.

The Ideal Gas Law

The relationship between volume, pressure, temperature and quantity of a gas, including definition of gas density.

Total and Partial Pressure - Dalton's Law of Partial Pressures

How to calculate total pressure and partial pressures for gas mixtures from Ideal Gas Law.

Water Vapor - Specific Heat vs. Temperature

Specific heat of Water Vapor - H2O - at temperatures ranging 175 - 6000 K.

Wet Steam - Enthalpy

Wet steam, dryness fraction and enthalpy.

Wet Steam - Quality vs. Dryness Fractions

Introduction and definition of steam quality and dryness fraction including calculating wet steam enthalpy and specific volume.

Wet Steam - Specific Volume

Wet steam and specific volume.

Sponsored Links

Search Engineering ToolBox

  • the most efficient way to navigate the Engineering ToolBox!

SketchUp Extension - Online 3D modeling!

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!


We don't collect information from our users. Only emails and answers are saved in our archive. Cookies are only used in the browser to improve user experience.

Some of our calculators and applications let you save application data to your local computer. These applications will - due to browser restrictions - send data between your browser and our server. We don't save this data.

Google use cookies for serving our ads and handling visitor statistics. Please read Google Privacy & Terms for more information about how you can control adserving and the information collected.

AddThis use cookies for handling links to social media. Please read AddThis Privacy for more information.