Tempertaure and Vacumm

http://en.wikipedia.org/wiki/Boiling_point

http://www.simetric.co.uk/si_steam.htm

http://en.wikipedia.org/wiki/Dew_point

http://en.wikipedia.org/wiki/Partial_pressure

http://en.wikipedia.org/wiki/Latent_heat

http://en.wikipedia.org/wiki/Steam

http://en.wikipedia.org/wiki/Water_vapour

The boiling temperature of water varies with pressure. If a partial vacuum is applied, the boiling temperature drops. The converse is also true: if a pressure is applied, by containing the steam in some way, then the boiling temperature increases.

A recommended publication is Mayhew & Rogers, "Thermodynamic Properties of Steam". It's pages are full of useful numbers and it would form an important part of the technical library of food processing, among many other fields. A handy condensed version (sorry for the pun!) is available at the simetric address that Guest has kindly posted above.

In simple terms it is the same as water boiling on top of a mountian, the common link to these two is the vapour pressure between the air and the liquid, the basic reason why liquid remains liquid is the pressure of the air onto the surface of the fluid, this state is at equilibrium, if the pressure above the liquid is reduced it allows the liquid molecules near the surface to escape, this you will see as evaporation, as the pressure above and around the liquid decreases the more the vapour, this intern starts moulecules not just on the surface to try to escape as they gain enery they move around more ( this is gass ) and are allowed to escape with less energy holding the fluid surface together.

hope this helps

The molecules of a liquid are forced to remain close to each other because of the pressure around it. If this pressure is reduced they tend to evaporate and become vapor in which the molecules are far apart.

At the same time the molecules of a liquid are in constant vibration which increases with temp. In general therefore as the temperature increases, the vibration increases and at a particular temp. called boiling point the molecules break free and become vapor.

Therefore either by keeping pressure constant and increasing temp. or by reducing pressure surrounding a liquid at any particular temperature, one can create boiling i.e. turning liquid to vapor.

thank you sir for ur discussion

but 8i got one doubt as u said that keeping pressure constant or tempertaure constant as u mentioned in the discussion but take one good example like pressure cooker here pressure is keep on increasing with rise in temperature.can u comment on this doubt plz

Thanking you

"Boiling," in any liquid is merely the result of the vapor pressure within the liquid exceeding the atmospheric pressure in which the liquid exists. With water at sea level, "boiling" occurs at 212 F (100 C). When you reduce the atmospheric pressure on the liquid (introduce a vacuum into the pressure vessel), the external pressure opposing the vapor pressure is reduced, hence, less heat is required to raise the liquids vapor pressure above this opposing pressure.

** Heat raises the pressure in a liquid due to the fact that heated materials expand as they absorb heat.

the eguation of state is the ideal principle behind this phenomenon. the boiling point of a fliud is inherently a state property and as such depends so much upon the pressure on the fluid. Assumed you have 1000 sheep in a relatively small pen which has a small opening. the size of the opening determines the number of sheep that comes out at a time. thus the size of the pressure on the water determines the number water molecules that comes out(evaporation). the greater the pressure(smaller opening) the smaller the number of molecules that come out(less evaporation)

what about the pressure cooker principle

In a pressure cooker, boiling takes place at a higher pressure than atmospheric. So the temperature of the contents runs higher than atmospheric boiling temperature because of the variation of the boiling temperature of water with pressure. The higher temperatures that a pressure cooker can achieve means the food cooks faster, and less energy is used to do it.

As a domestic investment, the pressure cooker can pay for itself in terms of reduced fuel bills in a matter of months, provided the local operators can be convinced of the efficacy of doing so. The time saved can be an added bonus.

cool. I knew this but didn't know how to say it as plainly as you contributors.

Pressure= amount particle

Temperature= particle energy average

then low pressure -> low amount particle -> low energy average -> Low Temperature