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General Science => General Science => Topic started by: CZARCAR on 26/04/2011 13:11:31

Title: How does water pressure change with increasing temperature?
Post by: CZARCAR on 26/04/2011 13:11:31
5 gal water in a sealed container [boiler]. temp of boiler water rises from 50*f to 200*f.......i assume the 50* pressure would be 0? what pressure @ 200*f?

what pressure @212*f? thanx
Title: Re: How does water pressure change with increasing temperature?
Post by: Madidus_Scientia on 26/04/2011 14:25:11
Homework question?
Title: Re: How does water pressure change with increasing temperature?
Post by: CZARCAR on 26/04/2011 21:36:54
Quote from: Madidus_Scientia on 26/04/2011 14:25:11
Homework question?
is this a stupid question or a stupid answer?
Title: How does water pressure change with increasing temperature?
Post by: Bored chemist on 27/04/2011 17:19:58
The pressure would be high enough that the boiler would stretch. So the answer depends on the design of the boiler.
A very rough figure would be 500 M Pa or roughly 5000 atm.
Oops! I think I miscounted the zeros.
About 500 Atmospheres.
Title: How does water pressure change with increasing temperature?
Post by: imatfaal on 28/04/2011 13:13:30
Wow - proof that even Homer nods.  Congrats (if that's the right sentiment) on neilep level
Title: How does water pressure change with increasing temperature?
Post by: Geezer on 28/04/2011 18:07:03
Proof that BC needs to get a life more like. Oh, wait a minute........
Title: How does water pressure change with increasing temperature?
Post by: lightarrow on 30/04/2011 14:02:41
Quote from: CZARCAR on 26/04/2011 13:11:31
5 gal water in a sealed container [boiler]. temp of boiler water rises from 50*f to 200*f.......i assume the 50* pressure would be 0? what pressure @ 200*f?

what pressure @212*f? thanx
Is there air inside or just water? If it's just water it's simple: look for vapour pressure at different temperatures:

50F =  10°C   --> 0.012 atm
200F = 93.3°C --> 0.79 atm
212F = 100°C  --> 1.00 atm
Title: How does water pressure change with increasing temperature?
Post by: Bored chemist on 30/04/2011 16:34:13
Plus the change in air pressure with temperature and also the fact that less air will dissolve in hot water, but the vapour pressure is the biggest change.
Title: How does water pressure change with increasing temperature?
Post by: lightarrow on 01/05/2011 13:06:51
With air inside, assuming for simplicity constant volume and ideal gas, its pressure variation from 50F to 212F can be computed from T in K: P2/P1 = T2/T1 = 373.15/283.15 = 1.32. Since P1 = 1.04 atm we have: P2 = 1.32*1.04 = 1.37 atm so the variation is 1.37-1.04 = 0.33 atm

Adding the vapour pressure, at 100°C the pressure inside is 1.37 + 1.00 = 2.37 atm.

This doesn't consider however the volume variation. Since some liquid water becomes vapour, the volume available for the gases increases and this reduces the air pressure, so the final result would be less than 2.37 atm.
Title: How does water pressure change with increasing temperature?
Post by: CZARCAR on 01/05/2011 20:20:26
thanx & i'm stupid but BC ur comment about "boiler stretch" lit why ive read other posts that say DONT SHUT THE BOILER DOWN 4 LEAKs & PRESSURE DIFFERENTIALS SEEMS TO BE THE ANSWER. i PATCHED EXPANSION TANK [INSTEAD OF DISCONNECTING IT & increasing boiler pressure] & maade ammends to suit
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