Water pressure vs temperature science question

[snailaquarium]

Hi,

Been a while since I went to school and I can't remember the answer to this query.

Is there a relationship between pressure and temperature of water in a closed system eg pressure cooker? Does the pressure have to go up with the temperature,, also is it possible for the temperature to be 95 and the pressure to go up if you manually add pressure but not increase the temperature ?

 

[mcordelia]

Yes, but you have to consider the gas part and the liquid part separately. Water is an incompressible fluid, and thus the pressure "caused by" the water will not change, but it will convey the pressure from it's surroundings (aka, hydraulics - pushing down on a piston at one end of a system will transmit the pressure through the fluid to the other end).

The gaseous phase is governed by the ideal gas law PV = NRT where you are able to calculate the partial pressure of the gas if you know the other terms. This part is a little more complicated because it's not a uniform gas ("air" mixed with water vapor,the concentration of which changes with temperature among other things). I think you can get a good approximation if you look up tables of relative humidity at certain temperatures / other conditions and go from there. I honestly don't remember how they go together through at this point so I think you have to do some googling past this bit and I can also ask a friend of mine who does this kind of stuff more regularly tomorrow if I get a hold of him.

Hopefully this is a start to get you the right google search terms to move you forward!