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Pressure due to volume change

by BuddyJim
Tags: pressure, volume
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BuddyJim
#1
Apr22-12, 12:49 PM
P: 3
Hi,

I have a closed system of fixed volume with an piston pump attached. The medium is air and the initial environmental condition are at standard atmospheric. I would like to know the formulas to use that would provide me with the new pressure when the piston is at top dead center (i.e. traveled a full stroke). Would I be correct in assuming that temperature is negligible when no heat (or fuel) is supplied to the system during the cycle?

Thanks
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aroc91
#2
Apr22-12, 03:07 PM
P: 161
If you know the initial volume and pressure, you would use P1V1=P2V2, where P1 and V1 are the initial pressure and volume and the other side of the equation is the pressure and volume after the piston has moved.

I would also say that temperature is negligible. It would change slightly, but it's not relevant because it's a result of the pressure change.
Bob S
#3
Apr23-12, 11:35 AM
P: 4,663
Quote Quote by aroc91 View Post
If you know the initial volume and pressure, you would use P1V1=P2V2, where P1 and V1 are the initial pressure and volume and the other side of the equation is the pressure and volume after the piston has moved.

I would also say that temperature is negligible. It would change slightly, but it's not relevant because it's a result of the pressure change.
Actually, air heats up as it is compressed, like in a diesel engine. Specifically for adiabatic compression, TV γ-1 = constant, where γ = 7/5 for air. There is a similar relation for the pressure increase. See http://en.wikipedia.org/wiki/Adiabatic_process

aroc91
#4
Apr23-12, 06:54 PM
P: 161
Pressure due to volume change

Quote Quote by Bob S View Post
Actually, air heats up as it is compressed, like in a diesel engine. Specifically for adiabatic compression, TV γ-1 = constant, where γ = 7/5 for air. There is a similar relation for the pressure increase. See http://en.wikipedia.org/wiki/Adiabatic_process
I know. I just meant that, from the description of the problem, temperature wasn't relevant, not that didn't occur.
gmax137
#5
Apr24-12, 01:27 PM
P: 844
Quote Quote by aroc91 View Post
If you know the initial volume and pressure, you would use P1V1=P2V2, where P1 and V1 are the initial pressure and volume and the other side of the equation is the pressure and volume after the piston has moved.

I would also say that temperature is negligible. It would change slightly, but it's not relevant because it's a result of the pressure change.
We can't say whether the temperature change is 'slight' unless we know the relative volumes between piston down and piston up, which the OP failed to mention.


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