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The vapor escapes to the laws from perfect gases.

The variations of the parameters such as "density, rate of flow, etc," cannot be expressed by simple formulas.

Lexicon employed for the steam (see steam table)

Effective pressure
or gauge pressure
The effective pressure or relative pressure is the pressure measured above the atmospheric pressure and read on the ordinary gauges pressure.
Absolute pressure: Absolute pressure = Gauge pressure + Atmospheric pressure (Atmospheric pressure at 1.01325 bar, i.e. normal atmospheric pressure on the sea level at 0C).
Boiling point: Temperature of saturated steam or also of boiling water under the same pressure.
Specific volume of steam: Volume occupied in m3 by 1 kg of steam.
Specific volume (or Density) of the steam: Specific mass of the steam in a volume of 1 m3.
Specific enthalpy
of liquid water:
Sensible Heat, it is the quantity of heat contained in 1 kg of water according to the selected temperature.
Specific enthalpy of the steam: It is the total heat contained in 1 kg of steam. It is the sum of the enthalpy of the various states, liquid (water) and gas (vapor).
Latent heat of vaporization:
Heat necessary to transform 1 kg of ebullient water into vapor without change of temperature (thermal energy necessary during the change of state liquid to the state vapor).
Specific heat of steam : Quantity of heat necessary to increase the temperature of one Celsius degree on a unit of mass of 1 kg of steam.
Dynamic viscosity : The viscosity of a fluid characterizes the resistance to the movement of the fluid.
Dry saturated steam Steam at the temperature of saturation, but not containing of water particles in suspension (seldom obtained in general)
Overheated steam Steam at a temperature higher than the temperature of saturation (dry steam). The temperature of an overheated vapor is not related to its pressure.
Condensates One usually calls " condensates " water resulting from the steam condensation.
Mass flow rate of the vapor In the installations of vapor one almost always uses the mass flow rate (kg/h or ton/h)

Dans le programme ThermoVapor, il y a module de calcul intégré qui permet d'établir toutes les caractéristiques physiques de l'eau, de la vapeur et de la vapeur surchauffée.

gaseous state (steam)(1)
Superheated state (steam) (2)
Physical properties of steam Superheated state of steam, water

Le calcul des caractéristiques physiques de la vapeur saturée (1) peut se faire soit à partir de la pression relative ou inversement en fonction de la température de la vapeur ou des deux paramètres dans le cas d'utilisation de la vapeur surchauffée (2)

Conventional designations of the types of heating

  • Heating with hot water: 0° < 110°C
  • Heating at high pressure of the water (or overheated water): 0° > 110°C
  • Low pressure steam (< = to 0.5 relative bar)
  • High pressure steam (> with 0.5 relative bar)

In the industrial facilities and domestics the vapor meets in 2 forms:

  • Saturated steam
  • Overheated steam

Recommendations for the installations of steam

Speeds are limited to:

  • Exhaust steam of the plant: 15 to 20 m/s.
  • Saturated vapor: wet saturated steam 15 to 35 m/s, dry saturated steam at 30 to 30 m/s.
  • Overheated vapor: 15 to 60 m/s, according to the diameter used.

For all piping (vapor, water), a minimal slope of 1 mm/m is respected, in the normal direction of flow of the fluid, in order to allow the extraction of the purging of it (vapor) and with 3 mm in the case of direction of contrary flow.

Recommendations for the installations of steam

The maximum temperature of the saturated steam at 0.5 relative bar is of 111.63 °C.

The steam pressure must be equal to the sum of the steam pressure necessary to the input of the transmitter of heat and the pressure losses in the steam pipes and all the accessories placed in the piping (Valves, filters, elbows, etc.)

  • the pressure losses are calculated only on the inlet circuit.
  • One admits in first study a linear resistance ranging between 50 to 60 Pa for the most underprivileged circuit. To avoid exceeding the 100 Pa in the rising mains)
  • Not to exceed a speed of 12 m/s in the vertical piping of the boiler
  • For all piping (vapor, water), a minimal slope of 1 mm/m is respected, in the normal direction of flow of the fluid, in order to allow the extraction of the purging of it (vapor) and with 3 mm in the case of direction of contrary flow.

Overheated steam:

The specific heat of the steam lies between 2.08 and 6.7 kj/kg °C (according to the pressure of use)

For the networks of big length the overheated vapor avoids the presence of condensates which can be formed only if the vapor is saturated.

That makes it possible to reduce the unnecessary thermal losses due to the cooling of piping.

The coefficient of transfer of the vapor in the course of désurchauffe is low compared to at the saturated vapor.

This property can impose the installation of a desurchauffor.

Example: Exchanger supplied with overheated steam at 190°C and water exit at 88°C. Under the pressure of use, the condensation of water occurs at 110°C

Knowing that the apparatus restores 12 liters of water per hour, what is the transmitted thermal power?

  • while cooling from 190 to 110°C, the steam provided = 80 X 1.965 = 157.2 kJ
  • while condensing at 110°C, it will restore = 2232 kJ
  • water while cooling from 110 to 88°C = 92.1 kJ
  • Total: (157.2 + 2232 + 92.1) X 12 = 29775.6 kJ/h (8271 W/h)

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