## properties of air under pressure.... question

## properties of air under pressure.... question

(OP)

If a volume of a gas (say, ambient atmospheric air) is reduced in a sealed container, to 1/2 of its original volume, doesn't it follow that the pressure would double?

Is this phenomenon linear in nature, all the way up to say, a 10:1 reduction in volume?

If it's NOT linear, why not? Would the rise in temperature due to compression have any effect on the pressure increase?

Thanks much for any information.

Bill Dedman in Hayward, CA

(billdedman@hotmail.com

Is this phenomenon linear in nature, all the way up to say, a 10:1 reduction in volume?

If it's NOT linear, why not? Would the rise in temperature due to compression have any effect on the pressure increase?

Thanks much for any information.

Bill Dedman in Hayward, CA

(billdedman@hotmail.com

## RE: properties of air under pressure.... question

Dig up a temperature-entropy diagram for air.

The perfect adiabatic process will be represented by a straight vertical line on the diagram.

## RE: properties of air under pressure.... question

It the air is compressed isentropically, the the pressure volume relationship will be P*V^k = constant. This occurs with a 100% efficient compression process and zero heat transfer. For air, k=1.4.

Most real processes will be a polytropic process, where P*V^n = constant. n will vary between 1 and k depending upon the process.

## RE: properties of air under pressure.... question

Simply P1V1T1=P2V2T2 therefore if the change in volume is slow enough to allow the heat liberated to dissipate then you can apply boyles law and state that should the volume be reduced by half then the pressure will double.

## RE: properties of air under pressure.... question

Cheers

Greg Locock