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Author Topic: Boiling Water? Engine only at 95 Deg?  (Read 2324 times)

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Ian_D

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Re: Boiling Water? Engine only at 95 Deg?
« Reply #15 on: 08 July 2008, 11:16:52 »
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wo cocked that up, why did it not boil over on previos occassions, is what i dont understand?

Strange isnt it eh?

Unless it wasn't quite as hot last few times Ive opened it?

I will open juist after I get back home tonight, see if it boils again! ;D

Question...

Useing the above theroy, why doesn't a bottle of coke get hot when you let the pressure out?

Say you have a bottle of pop at 20 deg and its at 30psi... When you undo the cap, the pressure drops to 14.7, that would mean that the temp would rise to 40.8 deg? Or have I got this wrong? :-/
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feeutfo

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Re: Boiling Water? Engine only at 95 Deg?
« Reply #16 on: 08 July 2008, 11:24:36 »
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water will release expanding air bubbles when boiling, under pressure the air can not expand, so no boiling or in this case bubbling.
hows that? :-/
this prob. applys more to the can of pop ;D
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Marks DTM Calib

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Re: Boiling Water? Engine only at 95 Deg?
« Reply #17 on: 08 July 2008, 11:25:48 »
No, you have not got it wrong......the heat in reality will be pretty quickly dissipated and hence is not really noticed.

In the case of an engine cooling system though its at the point where the water is almost boiling so what you see is a phase change from liquid to gas which is pretty violent.

What might have happened before is that the cap was removed a period of time after stopping and given the cooling system has a small leak, the pressures may have already equalised.

Many possible explanations
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feeutfo

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Re: Boiling Water? Engine only at 95 Deg?
« Reply #18 on: 08 July 2008, 11:35:01 »
bubbles/steam=expansion
under pressurse=no expansion. hence no steam/bubbles????
 
learning more on here than at school, probably koz i was over the fields on me bike ;D
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Entwood

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Re: Boiling Water? Engine only at 95 Deg?
« Reply #19 on: 08 July 2008, 12:33:09 »
Quote
Quote
wo cocked that up, why did it not boil over on previos occassions, is what i dont understand?

Strange isnt it eh?

Unless it wasn't quite as hot last few times Ive opened it?

I will open juist after I get back home tonight, see if it boils again! ;D

Question...

Useing the above theroy, why doesn't a bottle of coke get hot when you let the pressure out?

Say you have a bottle of pop at 20 deg and its at 30psi... When you undo the cap, the pressure drops to 14.7, that would mean that the temp would rise to 40.8 deg? Or have I got this wrong? :-/

Totally different ... in coke the CO2 (Carbon Dioxide) is in solution with the liquid and held there by pressure, when you take the cap off it comes out of solution as bubbles .. there is no heat transfer whatsoever.

The water v pressure is to do with boiling point of water .. which is higher under pressure and lower with reduced presure ... try making a cup of tea on a mountain .. tastes crap as the water is not hot enough.

The whole point of pressurising a cooling sysetm is to raise the boiling point in order to reduce evaporation losses, when you take the pressure away the water boils .. instantly
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Ian_D

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Re: Boiling Water? Engine only at 95 Deg?
« Reply #20 on: 08 July 2008, 14:51:03 »
I know im going off track now, but if I got a bottle water, pressurised it to say 50psi, then heated it up to 50 degress... what would happen when I released the pressure? would it get hotter still? MS Excel says 170.0680272 degrees???  :-/
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Entwood

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Re: Boiling Water? Engine only at 95 Deg?
« Reply #21 on: 08 July 2008, 16:07:01 »
Nothing at all would happen ... if it was 100 cc of water at 0 C when you started.. and you heated it to 50 C .. you have added 50 * 100 = 5000 calories .. it would remain at 50 C.

If you added 10000 calories you would heat it to 100 C and it would be on the edge of boiling, nothing else would  happen .. it would remain at 100 C.

If you added 12000 calories it would now try to boil at 100 C as each the added calories would boil off water at the rate of 600 calories /gram ( the latent heat of vapourisation). As the bottle is pressurised this doesn't happen .. and the temperature of the water would continue to rise by 20 degrees so the water would sit at 120C.

As soon as you release the pressure the evaporation takes place instantaneously ... 2000 calories excess at 600  cals/gram , so 3.33 cc of water instantly turn to steam at 120 C  ...

3.33 cc of water is  about 7.5 litres of water vapour (22.4 l/mol) ....

So when it goes .. it goes !! If you want 7.5 litres of superheated steam attacking you .. try the experiment !!! But have an ambulance nearby !!

(The above is somewhat simplified as the pressure in the bottle will change as well .. but I'm trying to give an idea .. not a calculation .. )  :)
« Last Edit: 08 July 2008, 16:21:00 by entwood »
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Andy B

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Re: Boiling Water? Engine only at 95 Deg?
« Reply #22 on: 08 July 2008, 17:04:13 »
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Nothing at all would happen ... if it was 100 cc of water at 0 C when you started.. and you heated it to 50 C .. you have added 50 * 100 = 5000 calories .. it would remain at 50 C.

If you added 10000 calories you would heat it to 100 C and it would be on the edge of boiling, nothing else would  happen .. it would remain at 100 C.

If you added 12000 calories it would now try to boil at 100 C as each the added calories would boil off water at the rate of 600 calories /gram ( the latent heat of vapourisation). As the bottle is pressurised this doesn't happen .. and the temperature of the water would continue to rise by 20 degrees so the water would sit at 120C.

As soon as you release the pressure the evaporation takes place instantaneously ... 2000 calories excess at 600  cals/gram , so 3.33 cc of water instantly turn to steam at 120 C  ...

3.33 cc of water is  about 7.5 litres of water vapour (22.4 l/mol) ....

So when it goes .. it goes !! If you want 7.5 litres of superheated steam attacking you .. try the experiment !!! But have an ambulance nearby !!

(The above is somewhat simplified as the pressure in the bottle will change as well .. but I'm trying to give an idea .. not a calculation .. )  :)

My head's beginning to hurt! :-? All far too long ago, as said I can only remember s=ut + .........  ;D  ;D  :y
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philhoward

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Re: Boiling Water? Engine only at 95 Deg?
« Reply #23 on: 08 July 2008, 21:13:18 »
The moving water (past the sensor) could well have been at 96 degrees, but the metal its cooling could be over 100 degrees.  Remove the pressure which is preventing it boiling and low behold..

Anyone ever done a Science experiment at school?  Making milk boil at room temperature...just add a vaccuum!
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feeutfo

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Re: Boiling Water? Engine only at 95 Deg?
« Reply #24 on: 09 July 2008, 00:50:15 »
 
Quote
I know im going off track now, but if I got a bottle water, pressurised it to say 50psi, then heated it up to 50 degress... what would happen when I released the pressure? would it get hotter still? MS Excel says 170.0680272 degrees???  :-/

still or sparkling?;D
« Last Edit: 09 July 2008, 00:51:36 by chrisgixer »
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SWMBO

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Re: Boiling Water? Engine only at 95 Deg?
« Reply #25 on: 09 July 2008, 10:31:09 »
lol, I love this site, girlies weren't allowed to do physics at my school (yeah I'm ancient and my school was even more so) so I'm learning a lot too lol.
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psychnurse

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Re: Boiling Water? Engine only at 95 Deg?
« Reply #26 on: 09 July 2008, 10:37:07 »
I was made to do a BSc Chemistry and I hated it!! Did it as part of my first job in order to get a pay rise and some prospects. Absoulutly detested it!!! Managed a 2:1 so not all bad.... just cannot be doing with it!!!

Phamacology was much better  :y :y :y Although the chemistry helped lots  :-[
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JueV6

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Re: Boiling Water? Engine only at 95 Deg?
« Reply #27 on: 09 July 2008, 10:39:19 »
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lol, I love this site, girlies weren't allowed to do physics at my school (yeah I'm ancient and my school was even more so) so I'm learning a lot too lol.


Something else you said that I agree with.... ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D
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psychnurse

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Re: Boiling Water? Engine only at 95 Deg?
« Reply #28 on: 09 July 2008, 10:40:19 »
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Quote
lol, I love this site, girlies weren't allowed to do physics at my school (yeah I'm ancient and my school was even more so) so I'm learning a lot too lol.


Something else you said that I agree with.... ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D





You will be in the dog house......  ;D ;D ;D
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