on . Posted in Thermodynamics

matter phasesSteam, abbreviated as STM, is the invisible vapor (gas) when water is heated to its boiling point and passes from a liquid to a gaseous state.  As water is heated and approaches its boiling point, some of the molecules attain kinetic energy enough to escape into the space above the surface of the liquid.  The more the water is heated the more molecules excapes.  When more molecules leave the liquid than enter the liquid, the saturation point is reached.  As the temperature continues to rising it reaches superheated steam where no liquid exists.  The temperature at which water boils and turns into steam depends on the pressure applied to it . At standard atmospheric pressure (1 atmosphere or 101.3 kilopascals), water boils at 100 degrees Celsius (212 degrees Fahrenheit), resulting in the formation of steam.

Steam has several unique properties and behaviors.  It occupies a greater volume than an equivalent mass of liquid water, as the gas molecules are more spread out and less densely packed.  Steam is also less dense than air, making it rise and disperse quickly.

In addition to its applications in industrial processes and power generation, steam has played a crucial role in the development of thermodynamics and the study of heat transfer.  Steam engines, for instance, were historically significant in powering trains and other machinery during the industrial revolution.  Understanding the physics of steam involves concepts such as phase transitions, thermodynamics, heat transfer, and the behavior of gases.  It has practical implications in fields like engineering, energy production, and environmental science.

Steam Tables

Steam Types

  • Saturated Steam  -  Saturated steam is steam that is in equilibrium with liquid water at a given pressure and temperature.  It contains the maximum amount of moisture possible at that pressure and temperature.  Saturated steam is commonly used for heating, power generation, and industrial processes.
  • Superheated Steam  -  Superheated steam is steam that has been heated to a temperature higher than its saturation temperature for a given pressure.  It contains no liquid water and is typically used in processes where high temperature heat transfer is required, such as in steam turbines, drying operations, and certain chemical processes.
  • Wet Steam  -  Wet steam, also called saturated steam with liquid droplets, is a mixture of vapor and liquid water.  It occurs when saturated steam is partially condensed due to cooling or expansion.  Wet steam can be problematic in some applications as the liquid droplets can cause erosion and damage to equipment.
  • Dry Steam  -  Dry steam is steam that contains no liquid water and is completely vaporized.  It is typically preferred for many applications because it provides more efficient heat transfer and avoids issues associated with wet steam.
  • Flash Steam  -  Flash steam is produced when high pressure condensate is suddenly released to a lower pressure, causing some of the liquid condensate to instantaneously vaporize.  It is often used in steam systems for heating or to recover energy from condensate.

These steam types have different characteristics and are used in various industrial, commercial, and residential applications depending on the specific requirements of the process or system.

Steam Quality

Steam quality, also called steam purity or dryness fraction, refers to the amount of moisture or liquid water present in steam.  It is a measure of how "dry" or "wet" the steam is.

Steam quality is expressed as a percentage or a fraction and represents the ratio of the mass of steam to the total mass of steam and water (steam + water) in a given sample.  A steam quality of 100% indicates completely dry or saturated steam with no liquid water present, while a steam quality of 0% indicates that the steam is entirely composed of liquid water.

Steam quality is an important parameter in various industrial processes and applications.  In some cases, such as power generation or steam turbine operation, it is crucial to have dry or high quality steam to ensure efficient and reliable performance.  Wet or low quality steam with excessive moisture can cause issues like erosion, corrosion, and reduced heat transfer efficiency.

The measurement and control of steam quality are typically performed using specialized instruments called steam quality meters or separators.  These devices separate the liquid and vapor phases of steam and determine the percentage of moisture content present.  Various factors can affect steam quality, including the design and operation of steam generation systems, boiler performance, water treatment, and steam distribution.  Proper maintenance and control of these factors are essential to achieve and maintain the desired steam quality for specific applications.

Steam Uses 

Steam is used for many things in piping design.  In the oil and gas industry, steam is used to heat production tanks, keep flow lines from freezing and to increase oil production in formations that are very viscious.  In other industries, it can be used to sterilize & clean equipment, sterilize equipment, and in reboilers which maintain tight tolerances on their temperatures.  Because of this, it is important to ensure that the line has been sized properly to reduce pressure drop and to also ensure that right steam qualitypressure and temperature is being delivered where it is supposed to.  Sizing a line too small will cause the water vapor and liquid to travel too fast which will reduce overall pressure in the line.  If the line is too large, the fluid and vapor will travel slower and heat loss will occur.  Equally important to sizing a line, sizing a valve for use in steam service.

Steam has a wide range of applications across various industries due to its unique properties, including its ability to carry large amounts of heat energy and its versatility.

  • Heat Transfer  -  Steam is widely used as a heat transfer medium in various industrial processes, HVAC systems, and power generation.  It carries a significant amount of latent heat, making it an efficient means of transferring energy.
  • Power Generation  -  Steam is a primary working fluid in many power plants, particularly in thermal power plants.  It is used to turn turbines, which generate electricity.  The most common method involves heating water to produce steam, which then drives turbines connected to generators.
  • Industrial Processes  -  Many industrial processes use steam for heating, sterilization, drying, and cleaning.  Industries such as chemical, pharmaceutical, food and beverage, textile, and pulp and paper utilize steam in various stages of their manufacturing processes.
  • Heating Systems  -  Steam is used for space heating in buildings, including residential, commercial, and institutional facilities.  Steam heating systems involve the distribution of steam through pipes to radiators or other heat exchangers.
  • Mechanical Power  -  Steam engines have been historically used for mechanical power in applications such as locomotives and ships.  While steam engines have been largely replaced by more efficient technologies, some specialized applications still use them.
  • Cleaning and Sterilization  -  Steam is an effective agent for cleaning and sterilizing surfaces and equipment.  It is commonly used in hospitals, laboratories, and food processing facilities for sterilizing medical instruments, laboratory equipment, and food processing equipment.
  • Humidity Control  -  Steam can be used to humidify air in controlled environments such as greenhouses and certain industrial processes where precise humidity levels are required.
  • District Heating  -  In some urban areas, steam is used in district heating systems to provide heat to multiple buildings from a centralized source.  This is common in cities where excess steam from power generation is utilized for heating purposes.
  • Oil Recovery  -  Steam injection is employed in enhanced oil recovery (EOR) processes to improve the flow of heavy or viscous crude oil in underground reservoirs.
  • Food Preparation  -  Steam is commonly used in cooking processes, such as steaming vegetables, cooking rice, or baking bread.  It is favored for its ability to cook food evenly and retain nutrients.
  • Textile Industry  -  Steam is widely used in the textile industry for processes such as dyeing, drying, and finishing of fabrics.

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