I'm working on a project and need some input for how a fluid behaves when compressed. I'm a layman, so please try to keep answers layman-esque.

Here's the setup: imagine you've got a double acting hydraulic cylinder with one outlet hooked up to your hydraulic system and the other a closed system of a gas. These two systems (gas and hydraulic) are both separate, closed systems. They intersect at the cylinder, but do not actually ever connect with each other (one of the systems pushes the piston forward, and the other pushes it back)

You then add gas into the gas system, increasing pressure to the the gas side of cylinder, causing a backstroke. When the cylinder completes the stroke, you turn on the hydraulics, which pushes the piston forward, dumping the gas from the cylinder into the gas system. You repeat this process indefinitely.

My question: does heat get created by the action of the hydraulics forcing gas through the small hole of the cylinder outlet and into the gas system (we're talking high pressures, 1500-2000 psi).? Does the heat dissipate naturally, or would it collect and build and need to be removed? or would the heat equation be a wash (I. e. would the heat created by the hydraulic powered frontstroke be offset by an equal amount of heat loss during the gas powered back stroke)?

Would the work of the hydraulic system forcing the gas through the small hole back into the resoirvoir create heat in the gas (or fluid) itself?

Hopefully this isn't too confusing. Any help would be appreciated.

  • 1
    $\begingroup$ Yeah I know its confusing lol. If I don't get one I'll make up a diagram and repost it. Tks $\endgroup$
    – RobA
    Commented Feb 8, 2017 at 19:34

1 Answer 1


There should be minimal heat gain.

There will be some heat from all the friction of movement (both in the pistons and just the air flowing through things in general). Ideally it will have minimal losses though; so any heat that it builds up would easily escape through dissipation.

The more orifices and stuff that you put it through the worse the heat losses will be.

As far as the ideal gas law goes; the pressure and volume should be all that significantly changes, while $T_1$ and $T_2$ remain approximately the same.


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