Vapor and Steam
An introduction to vapor and steam.
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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
- 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
- Vapor at the temperature of the boiling point corresponding to its pressure.
- Properties of Saturated Steam - Imperial Units
- Properties of Saturated Steam - SI Units
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.
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Steam and Condensate
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Related Documents
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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 Mixture
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. -
Flash Steam Generation (bar)
The amount of flash steam generated depends on steam pressure and pressure in the condensate lines. -
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 with 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. -
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.
