Previous in Forum: The Problem With EV Charging Units   Next in Forum: Up-cycled aluminum cans
Close
Close
Close
24 comments
Guru
Hobbies - RC Aircraft - New Member

Join Date: Aug 2007
Posts: 850
Good Answers: 9

Volume Of a Sphere, vs Pressure

04/12/2022 9:20 AM

OK say you have a sphere with a volume of 14 cubic meters.

How much volume do you need to add to this sphere so the pressure differential inside vs outside of the sphere has 0.4 PSI now?

Thanks!

Joe

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
2
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 30259
Good Answers: 816
#1

Re: Volume Of a Sphere, vs Pressure

04/12/2022 9:24 AM

If the wall is a liquid, it depends upon the surface tension.

If the wall is a solid, it depends on its modulus of elasticity and its thickness; if it is made of thin rubber, then rather more volume will be needed than if it is made of thick steel.

It also depends upon temperature. Adding volume to increase the pressure will also increase the temperature.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply Good Answer (Score 2)
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 30259
Good Answers: 816
#5
In reply to #1

Re: Volume Of a Sphere, vs Pressure

04/12/2022 10:23 AM

It also depends on the nature of the stuff that is being added to the <...sphere...> to create the pressure difference.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply Score 1 for Good Answer
Guru
Hobbies - RC Aircraft - New Member

Join Date: Aug 2007
Posts: 850
Good Answers: 9
#2

Re: Volume Of a Sphere, vs Pressure

04/12/2022 9:46 AM

Morning PW,

HI!

Yeah Mr. Balloon here. think a non stretching sphere. Yeah I know the temp will rise some, but at that pressure difference I don't think it would be much.

Joe

Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 30259
Good Answers: 816
#4
In reply to #2

Re: Volume Of a Sphere, vs Pressure

04/12/2022 10:22 AM

<....non stretching sphere...>

This universe doesn't work that way.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
Engineering Fields - Nuclear Engineering - New Member

Join Date: Sep 2009
Location: Louisville, OH
Posts: 1523
Good Answers: 29
#14
In reply to #4

Re: Volume Of a Sphere, vs Pressure

04/12/2022 11:23 PM

Why not use simplifying assumptions. Sorta like the frictionless pulleys in physics class. Therefore, a non-stretching steel sphere with no temperature rise. Then refine if you want.

__________________
Lehman57
Register to Reply Score 1 for Good Answer
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 30259
Good Answers: 816
#19
In reply to #14

Re: Volume Of a Sphere, vs Pressure

04/13/2022 8:29 AM

<...assumptions...want...>

A better definition of the problem would avoid the need to guess these things.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
2
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 30805
Good Answers: 1722
#3

Re: Volume Of a Sphere, vs Pressure

04/12/2022 9:58 AM

Probably don't need to add any at all, just raise the temperature a bit..

https://opentextbc.ca/chemistry/chapter/9-2-relating-pressure-volume-amount-and-temperature-the-ideal-gas-law/

__________________
Break a sweat everyday doing something you enjoy
Register to Reply Good Answer (Score 2)
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 30259
Good Answers: 816
#6
In reply to #3

Re: Volume Of a Sphere, vs Pressure

04/12/2022 10:24 AM

Exactly. Zero needs to be added if the temperature change is adequate. GA

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 30805
Good Answers: 1722
#9
In reply to #3

Re: Volume Of a Sphere, vs Pressure

04/12/2022 11:50 AM

__________________
Break a sweat everyday doing something you enjoy
Register to Reply Score 1 for Good Answer
3
Guru

Join Date: Apr 2010
Location: About 4000 miles from the center of the earth (+/-100 mi)
Posts: 8997
Good Answers: 1023
#7

Re: Volume Of a Sphere, vs Pressure

04/12/2022 10:38 AM

Assume the sphere initially has 14.7 psi.

Assume the temperature remains the same.

P1V1/T1 = P2V2/T2 or P1V1 = P2V2 : V2=V1*P1/P2

V1=14, P1=14.7, P2=14.7-0.4=14.3

V2=14 * 14.7 / 14.3 = 14.39 cu meters

Register to Reply Good Answer (Score 3)
Guru
Hobbies - RC Aircraft - New Member

Join Date: Aug 2007
Posts: 850
Good Answers: 9
#8
In reply to #7

Re: Volume Of a Sphere, vs Pressure

04/12/2022 10:44 AM

Ok it Looks like I need to give more details.

The sphere is at 60K feet ambient air pressure is 1.040159 Psi

temp is, -56 C

Register to Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 30805
Good Answers: 1722
#10
In reply to #8

Re: Volume Of a Sphere, vs Pressure

04/12/2022 11:51 AM

...and what gas is inside the balloon?

__________________
Break a sweat everyday doing something you enjoy
Register to Reply
Guru
Hobbies - RC Aircraft - New Member

Join Date: Aug 2007
Posts: 850
Good Answers: 9
#11
In reply to #10

Re: Volume Of a Sphere, vs Pressure

04/12/2022 11:57 AM

oops ambient "AIR" whatever The surrounding air around the sphere is made of.

Joe

And Thanks everyone!

Joe

Register to Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 30805
Good Answers: 1722
#13
In reply to #11

Re: Volume Of a Sphere, vs Pressure

04/12/2022 7:30 PM

~0.33 psi is the atmospheric pressure at that altitude and temperature...

https://www.mide.com/air-pressure-at-altitude-calculator

__________________
Break a sweat everyday doing something you enjoy
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 30259
Good Answers: 816
#16
In reply to #13

Re: Volume Of a Sphere, vs Pressure

04/13/2022 8:17 AM

=23 millibar...

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru

Join Date: Apr 2010
Location: About 4000 miles from the center of the earth (+/-100 mi)
Posts: 8997
Good Answers: 1023
#12
In reply to #8

Re: Volume Of a Sphere, vs Pressure

04/12/2022 1:23 PM

If temp is constant, pressure is inversely proportional to volume. Boyle's law works at any altitude.

Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 30259
Good Answers: 816
#15
In reply to #8

Re: Volume Of a Sphere, vs Pressure

04/13/2022 8:16 AM

=72 millibar...

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 30259
Good Answers: 816
#17

Re: Volume Of a Sphere, vs Pressure

04/13/2022 8:18 AM

=28 millibar...

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 30259
Good Answers: 816
#18

Re: Volume Of a Sphere, vs Pressure

04/13/2022 8:27 AM

It looks like at this juncture, the forum cannot agree on the ambient air pressure.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
Hobbies - RC Aircraft - New Member

Join Date: Aug 2007
Posts: 850
Good Answers: 9
#20
In reply to #18

Re: Volume Of a Sphere, vs Pressure

04/13/2022 9:17 AM

My Calculator at 60K feet says 71.71641 millibar

Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 30259
Good Answers: 816
#21
In reply to #20

Re: Volume Of a Sphere, vs Pressure

04/13/2022 10:11 AM

OK. So assuming the <...sphere...> doesn't change shape and the compression is isothermal, the <...volume...> needed at 72 millibar to raise the pressure to 100 millibar is 28/72x14m3.

However, it would take a substantial support structure at that altitude to support a <...sphere...> that doesn't change shape measurably as the internal pressure is raised by 100/78=28%, and the forum has no information about this.

Assuming it is a rather more flexible material <...Balloon...> and can change shape, the strength and the buoyancy of the material forming the <...sphere...> is also a factor for, as the pressure inside it increases and its volume increases, its weight does as well, therefore it becomes less buoyant and it is therefore likely to assume a lower altitude, thereby changing the volume and the pressure inside it during the descent.

Given the lack of clear starting conditions it is now easier to see how intractable this problem actually is.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 30259
Good Answers: 816
#22
In reply to #20

Re: Volume Of a Sphere, vs Pressure

04/14/2022 4:17 AM

Oh, and because it drops to a lower altitude, the ambient temperature goes up, which makes it expand as it does so.

International Standard Atmosphere.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru

Join Date: Jul 2016
Posts: 1037
Good Answers: 69
#23

Re: Volume Of a Sphere, vs Pressure

04/15/2022 1:55 AM

So, much like filling a tire. Don’t think the shape, I.e. sphere matters?

Register to Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 30805
Good Answers: 1722
#24

Re: Volume Of a Sphere, vs Pressure

04/15/2022 12:35 PM

__________________
Break a sweat everyday doing something you enjoy
Register to Reply
Register to Reply 24 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

Lehman57 (1); NSS (4); PWSlack (11); Rixter (2); rwilliams (1); SolarEagle (5)

Previous in Forum: The Problem With EV Charging Units   Next in Forum: Up-cycled aluminum cans

Advertisement