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Dive tart, just can't say no :-)
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Right Charles' law and how to calculate the pressure drop when a cylinder is filled to a specif pressure at a specific temperature then moved to a different temperature eg. cold water. The maths is messing my head up with the (P1xV1)/T1 = etc... can someone please explain this to me as if I was 6 years old and in a way that I can remember it. I've been hitting the books all day and maybe I'm tired and it will all drop into place when I'm fresh tomorrow but right now I'm tying myself up in knots. :embarassed:
 

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Dive tart, just can't say no :-)
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Discussion Starter · #2 ·
The boss is explaining it to me and my eyes just glaze over. I know there are some maths geniuses out there who will shake their heads and tut but I'm equally certain there are others who found this difficult too.
 

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You've got the equation - P1V1/T1 = P2V2/T2 - just drop the numbers in. The only constant is the volume (it's not exactly constant, but close enough for jazz).

The problem here is, you don't know the temperature inside the cylinder when the fill is hot, but if you fill slowly and allow to cool, assume it's at ambient.

Note that the temperatures are Kelvin here as they need to be absolute.
 

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Dive tart, just can't say no :-)
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9,453 Posts
Discussion Starter · #4 ·
You've got the equation - P1V1/T1 = P2V2/T2 - just drop the numbers in. The only constant is the volume (it's not exactly constant, but close enough for jazz).

The problem here is, you don't know the temperature inside the cylinder when the fill is hot, but if you fill slowly and allow to cool, assume it's at ambient.

Note that the temperatures are Kelvin here as they need to be absolute.
Cheers Nick, I understand that in theory, The example I have is a cylinder filled to 200 bar at ambient temp of 26c then dropped into water of 7c. I know I need to add 1 to the pressure thus 201 bar to account for surface pressure, I know that I need to convert C to kelvin thus adding 273 to both temperatures to arrive at a kelvin figure but I'm in a mess from there on. I'm sure that you or pretty much most people could give me the answer but I need to get my head round doing it for myself.
 

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Example: 12l cylinder, air temp is 30C, water temp is 20C and fill is 240 barg.

240*12/303 = x*12/293

swap the numbers around:

9.5 * 293 / 12 = x

x = 232 barg
 

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Cheers Nick, I understand that in theory, The example I have is a cylinder filled to 200 bar at ambient temp of 26c then dropped into water of 7c. I know I need to add 1 to the pressure thus 201 bar to account for surface pressure, I know that I need to convert C to kelvin thus adding 273 to both temperatures to arrive at a kelvin figure but I'm in a mess from there on. I'm sure that you or pretty much most people could give me the answer but I need to get my head round doing it for myself.
You can leave the cylinder size out to make the numbers easier. In your example:

200/299 = x/280

200*280/299 = x

x = 187.3
 

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From this you can see that the equation, assuming constant volume, is always:

New pressure = Old pressure * new temp / old temp
 

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Beach-bum-Blonde Mafia ;o)
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What temperature is the whiskey?
I drank all the whiskey, he's just got the whisky - the temperature is a bit superfluous in this example ;)
 
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