# The Naked Scientists Forum

### Author Topic: How does water pressure change with increasing temperature?  (Read 12351 times)

#### CZARCAR

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##### How does water pressure change with increasing temperature?
« 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
« Last Edit: 26/04/2011 22:56:02 by chris »

• Neilep Level Member
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##### Re: How does water pressure change with increasing temperature?
« Reply #1 on: 26/04/2011 14:25:11 »
Homework question?

#### CZARCAR

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##### Re: How does water pressure change with increasing temperature?
« Reply #2 on: 26/04/2011 21:36:54 »
Homework question?
is this a stupid question or a stupid answer?

#### Bored chemist

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##### How does water pressure change with increasing temperature?
« Reply #3 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.
« Last Edit: 28/04/2011 12:50:11 by Bored chemist »

#### imatfaal

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##### How does water pressure change with increasing temperature?
« Reply #4 on: 28/04/2011 13:13:30 »
Wow - proof that even Homer nods.  Congrats (if that's the right sentiment) on neilep level

#### Geezer

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##### How does water pressure change with increasing temperature?
« Reply #5 on: 28/04/2011 18:07:03 »
Proof that BC needs to get a life more like. Oh, wait a minute........

#### lightarrow

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##### How does water pressure change with increasing temperature?
« Reply #6 on: 30/04/2011 14:02:41 »
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
« Last Edit: 30/04/2011 14:04:15 by lightarrow »

#### Bored chemist

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##### How does water pressure change with increasing temperature?
« Reply #7 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.

#### lightarrow

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##### How does water pressure change with increasing temperature?
« Reply #8 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.

#### CZARCAR

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##### How does water pressure change with increasing temperature?
« Reply #9 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
SAY HI TO MOMS & THE MOFOS without whom MOMS............NEVER MIND...........VVV

#### The Naked Scientists Forum

##### How does water pressure change with increasing temperature?
« Reply #9 on: 01/05/2011 20:20:26 »