منتدى الهندسة الكهربية - عرض مشاركة واحدة

Khaled Hamza · #1 12-28-2010, 04:40 PM

Why Hydrogen Gas is the Best COOLING medium for rotating machines?

Utilizati** of Hydrogen gas as the cooling medium either for inner-cooled or for c**venti**al type hydrogen cooled units has the following advantages:
1) Hydrogen gas is small in density; therefore decrease windage and ventilati** loss.
2) Hydrogen gas has large thermal c**ductivity and surface heat transfer coefficient, Therefore, the output per unit volume of active material will increase and the limit of maximum practical rating can be made larger than with an air-cooled unit.
3) Freedom from oxygen and moisture results in little cor**a effect, thereby prol**ging the insulati** life of the stator coil.
4) Small gas density and closed ventilating system will reduce noise.
5) Hydrogen-cooled machine is c**venient for c**verting into an outdoor type.

-Comm** gases which are much lighter than air are (hydrogen and helium). Although helium is inert n**-flammable, and an ideal medium for ventilating purposes, it cannot be obtained in quantities, which makes its price high and makes it unsuitable as cooling medium,
-** the c**trary, hydrogen can be obtained rather inexpensively, and it has advantages over helium in having a small density and better thermal characteristics.

SFETY NOTE.
-The intensity of explosi** of an air-hydrogen mixture varies with the proporti** of the two gases present, and also has to do with the gas pressure.
-A curve ** which the values of intensity are plotted against the properties of gases will be approximately a sine wave having zero values at (4 % and 75 % hydrogen), and reaching a maximum intensity in between.
-So we have to take care:-
*Hydrogen and air should never be mixed.
*Carb** dioxide should be used as an intermediate gas when changing air to hydrogen, or from hydrogen to air.
*When charging gas, provide vent to the atmosphere from generator.