Heat Formula Question

diverreb · 4th February 2008, 02:40

Anyone know a simple formula for finding approximate tank pressure at a given temperature? Pretty sure there's one out there, but it's been a while and I can't find it. Example: Tank has 3000 psi at 45 degrees F. What will the pressure be at 75 degrees F, 85 degrees F, etc. Does that vary with the mix of gases? Air vs O2 vs He.....

Thanks,

Richie

Gilles · 4th February 2008, 03:24

Off memory getting pretty old now....

P1V1/T1=P2V2/T2

Pressures in bar, Volume in L, and Temperature in deg Kelvin

Pressure will vary more with He than other gases mentioned because it is less compressible, pressure dependant factor around .85 for our uses.

Hope this helps (and is at least partially correct)

***diverklondike*** · 4th February 2008, 03:36

Ideal Gas Law...

Ideal gas law - Wikipedia, the free encyclopedia

cramerdn · 4th February 2008, 04:12

Quote: (Originally Posted by Gilles)

Off memory getting pretty old now....

P1V1/T1=P2V2/T2

Pressures in bar, Volume in L, and Temperature in deg Kelvin

Pressure will vary more with He than other gases mentioned because it is less compressible, pressure dependant factor around .85 for our uses.

Hope this helps (and is at least partially correct)

Actualy since V1 and V2 are equal you get P1/T1=P2/T2 or P1/P2=T1/T2

You can do it Bar and Kelvin or PSI and Rankin, whichever you prefer. For more acurate conversions you need Van Der Whals equations found in a P chem textbook but if you are only worried about changes in P for changes in T probably not worth the effort.

jaap · 4th February 2008, 07:14

Quote: (Originally Posted by diverreb)

Anyone know a simple formula for finding approximate tank pressure at a given temperature? Pretty sure there's one out there, but it's been a while and I can't find it. Example: Tank has 3000 psi at 45 degrees F. What will the pressure be at 75 degrees F, 85 degrees F, etc. Does that vary with the mix of gases? Air vs O2 vs He.....

Thanks,

Richie

Using imperial units is not my thing...

But have a look here: http://antoine.frostburg.edu/chem/se.../realgas.shtml

Just type in whatever units you like. Use N2 to approximate air. If you want to approximate various mixtures you could make linear combinations yourself from the data your get.

diverreb · 4th February 2008, 13:42

Thanks guys....

Richie

Mike Costanzo · 11th May 2008, 15:43

Yeah, what Mark said.

Tom Rose · 12th May 2008, 12:11

Quote: (Originally Posted by cramerdn)

Actualy since V1 and V2 are equal you get P1/T1=P2/T2 or P1/P2=T1/T2

You can do it Bar and Kelvin or PSI and Rankin, whichever you prefer. For more acurate conversions you need Van Der Whals equations found in a P chem textbook but if you are only worried about changes in P for changes in T probably not worth the effort.

Almost there guys but.......

Gotta take in consideration the temperature of the tank body, the mass of the tank body (and valve), the specific heat of the tank body (depends upon material), the final temperature of the tank body and insulate the tank from giving off heat during the change of pressure.

This plus the gas in the tank, and the gas added since the ideal gas law does not always work out with our breathing gases and pressures.

All of this depends upon how accurate you want the answer.....

Tom

4th February 2008, 02:40	#1 (permalink)
diverreb DE/MD/NJ Wreck Diver Current Rebreather/s: Optima Other Rebreather/s: Join Date: Mar 2007 Location: Dover, DE Posts: 517	Heat Formula Question Anyone know a simple formula for finding approximate tank pressure at a given temperature? Pretty sure there's one out there, but it's been a while and I can't find it. Example: Tank has 3000 psi at 45 degrees F. What will the pressure be at 75 degrees F, 85 degrees F, etc. Does that vary with the mix of gases? Air vs O2 vs He..... Thanks, Richie
(Offline)

4th February 2008, 03:24	#2 (permalink)
Gilles Worship the feminine Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Sep 2005 Location: Den Haag (Netherlands) Posts: 761	Re: Heat Formula Question Off memory getting pretty old now.... P1V1/T1=P2V2/T2 Pressures in bar, Volume in L, and Temperature in deg Kelvin Pressure will vary more with He than other gases mentioned because it is less compressible, pressure dependant factor around .85 for our uses. Hope this helps (and is at least partially correct) __________________ Gilles http://www.dirrebreather.com Last edited by Gilles : 4th February 2008 at 03:27.
(Offline)

4th February 2008, 03:36	#3 (permalink)
*diverklondike* Moderator Current Rebreather/s: Inspiration Classic Other CCR Other Rebreather/s: Inspiration Classic Other CCR Join Date: Oct 2005 Location: Delaware, USA Posts: 1,463	Re: Heat Formula Question Ideal Gas Law... Ideal gas law - Wikipedia, the free encyclopedia
(Offline)

4th February 2008, 04:12	#4 (permalink)
cramerdn Living The Dream, Baby!! Current Rebreather/s: Evolution Dolphin Other Rebreather/s: Dolphin Join Date: Dec 2006 Location: Townsville QLD Posts: 458	Re: Heat Formula Question Quote: (Originally Posted by Gilles) Off memory getting pretty old now.... P1V1/T1=P2V2/T2 Pressures in bar, Volume in L, and Temperature in deg Kelvin Pressure will vary more with He than other gases mentioned because it is less compressible, pressure dependant factor around .85 for our uses. Hope this helps (and is at least partially correct) Actualy since V1 and V2 are equal you get P1/T1=P2/T2 or P1/P2=T1/T2 You can do it Bar and Kelvin or PSI and Rankin, whichever you prefer. For more acurate conversions you need Van Der Whals equations found in a P chem textbook but if you are only worried about changes in P for changes in T probably not worth the effort. __________________ "Its better to live one day as a tiger than an entire life as a worm." "But who's ever heard of a worm skin rug?"
(Online)

4th February 2008, 07:14	#5 (permalink)
jaap Normal people worry me Current Rebreather/s: Classic Kiss Other CCR RB80 / Clone Ray Other SCR Home Build Other Rebreather/s: Other CCR RB80 / Clone Ray Other SCR Home Build Join Date: Jun 2005 Location: Stockholm Sweden Posts: 438	Re: Heat Formula Question Quote: (Originally Posted by diverreb) Anyone know a simple formula for finding approximate tank pressure at a given temperature? Pretty sure there's one out there, but it's been a while and I can't find it. Example: Tank has 3000 psi at 45 degrees F. What will the pressure be at 75 degrees F, 85 degrees F, etc. Does that vary with the mix of gases? Air vs O2 vs He..... Thanks, Richie Using imperial units is not my thing... But have a look here: http://antoine.frostburg.edu/chem/se.../realgas.shtml Just type in whatever units you like. Use N2 to approximate air. If you want to approximate various mixtures you could make linear combinations yourself from the data your get. __________________ My initials: JAAP
(Offline)

4th February 2008, 13:42	#6 (permalink)
diverreb DE/MD/NJ Wreck Diver Current Rebreather/s: Optima Other Rebreather/s: Join Date: Mar 2007 Location: Dover, DE Posts: 517	Re: Heat Formula Question Thanks guys.... Richie
(Offline)

11th May 2008, 15:43	#7 (permalink)
Mike Costanzo Never E nuff Current Rebreather/s: Classic Kiss Other Rebreather/s: Classic Kiss Join Date: Apr 2007 Location: Berlin,Md/Port Salerno,Fl - USA Posts: 117	Re: Heat Formula Question Yeah, what Mark said. __________________ Mike Costanzo CK #318
(Offline)

12th May 2008, 12:11	#8 (permalink)
Tom Rose Still Learning Current Rebreather/s: Other CCR Home Build Other Rebreather/s: Prism Topaz Other CCR Home Build Join Date: Oct 2005 Location: USA,North Carolina Posts: 329	Re: Heat Formula Question Quote: (Originally Posted by cramerdn) Actualy since V1 and V2 are equal you get P1/T1=P2/T2 or P1/P2=T1/T2 You can do it Bar and Kelvin or PSI and Rankin, whichever you prefer. For more acurate conversions you need Van Der Whals equations found in a P chem textbook but if you are only worried about changes in P for changes in T probably not worth the effort. Almost there guys but....... Gotta take in consideration the temperature of the tank body, the mass of the tank body (and valve), the specific heat of the tank body (depends upon material), the final temperature of the tank body and insulate the tank from giving off heat during the change of pressure. This plus the gas in the tank, and the gas added since the ideal gas law does not always work out with our breathing gases and pressures. All of this depends upon how accurate you want the answer..... Tom __________________ The 50-50-90 rule: Anytime I have a 50-50 chance of getting something right, there's a 90% probability I'll get it wrong the first time. www.atlimp.com
(Offline)

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode