How Does Piston Movement Affect Pressure in a Closed System?

In summary, the conversation discusses using the formula P1V1=P2V2 to determine the new pressure in a closed system with a piston pump attached. The temperature change is considered negligible due to the lack of heat or fuel supplied during the cycle. However, it is noted that air heats up during compression and there is a specific relation for adiabatic compression. The exact temperature change cannot be determined without knowing the relative volumes.
  • #1
BuddyJim
3
0
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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  • #2
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.
 
  • #3
aroc91 said:
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, T·V 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
 
  • #4
Bob S said:
Actually, air heats up as it is compressed, like in a diesel engine. Specifically for adiabatic compression, T·V 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.
 
  • #5
aroc91 said:
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.
 

FAQ: How Does Piston Movement Affect Pressure in a Closed System?

1. What is pressure due to volume change?

Pressure due to volume change, also known as compressibility, is a measure of how much a substance's volume changes in response to a change in pressure. It is a property that is important in understanding the behavior of gases and liquids.

2. How is pressure due to volume change calculated?

Pressure due to volume change can be calculated using the formula P = (1/V)(dV/dP), where P is pressure, V is volume, and (dV/dP) is the change in volume with respect to change in pressure. This formula is also known as the isentropic compressibility equation.

3. What factors affect pressure due to volume change?

The compressibility of a substance is affected by several factors, including temperature, intermolecular forces, and molecular size. Generally, substances with weaker intermolecular forces and smaller molecules tend to be more compressible.

4. How does pressure due to volume change affect the behavior of gases?

In gases, pressure due to volume change can cause the gas to expand or contract, depending on the change in pressure. This can lead to changes in temperature and density, which can affect the overall behavior of the gas, such as its ability to dissolve in a liquid or its ability to flow through a pipe.

5. Can pressure due to volume change be negative?

Yes, pressure due to volume change can be negative. This occurs when the volume increases as the pressure decreases, such as when a gas expands. In this case, the change in volume is positive, but the negative pressure indicates that the gas is exerting a pulling or tension force rather than a pushing or compression force.

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