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
or gauge pressure
|The effective pressure
or relative pressure is the pressure measured above the atmospheric
pressure and read on the ordinary gauges pressure.
= Gauge pressure + Atmospheric pressure (Atmospheric pressure
at 1.01325 bar, i.e. normal atmospheric pressure on the
sea level at 0°C).
||Temperature of saturated
steam or also of boiling water under the same pressure.
in m3 by 1 kg of steam.
(or Density) of the steam:
||Specific mass of
the steam in a volume of 1 m3.
of liquid water:
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
of heat necessary to increase the temperature of one Celsius
degree on a unit of mass of 1 kg of steam.
||The viscosity of
a fluid characterizes the resistance to the movement of the
|Dry saturated steam
||Steam at the temperature
of saturation, but not containing of water particles in suspension
(seldom obtained in general)
||Steam at a temperature
higher than the temperature of saturation (dry steam). The temperature
of an overheated vapor is not related to its pressure.
||One usually calls
" condensates " water resulting from the steam condensation.
|Mass flow rate of
||In the installations
of vapor one almost always uses the mass flow rate (kg/h or
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)
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
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
- 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
- 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.
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
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)