Pressure change as it relates to temperature

[IreneReft]

I'm new to thermo and pneumatics so please go easy on me.

If someone could point me towards a good source of information that relates to the following problem I would appreciate it.

If I have a pneumatic system that is perfectly insulated (temperature) and I release air pressure.. Would the air get colder if I released it faster or would the speed at which I released the pressure not matter. i.e The air will be at the same temperature regardless of how fast it was released.

I guess what I'm looking for is a formula that relates flow to temperature drop or something along those lines.

Any help would be appreciated.

 

[MortenA]

Your flow velocity will not as such matter.

Best regards

Morten

 

[vpl]

As posted, this sounds like a homework problem. You might want to look in a thermo textbook.

Patricia Lougheed

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[Dave41A]

The ideal gas law is what you're looking for. PV=mRT. Any good undergraduate Thermo book will have it. Morten is right...flow rate does not matter for this problem due to the perfect insulation.

Good luck

 

[FeX32]

A good reference is of the likes of:

http://www.amazon.ca/Fundamentals-T...=sr_1_2?ie=UTF8&s=books&qid=1231774595&sr=8-2

or similar as the others mentioned.

TTFN,

Fe

 

[sailoday28]

If the volume containing the air is rigid, the temp within the volume will decrease as the mass dereases.
The faster the mass decreases, the faster, the temperature will decrease.

 

[IreneReft]

Thanks for the help everyone.

fex32 - Nice reference, but have anything a little more free.

I suppose the part of the ideal gas law I don't understand is if the volume increases by x, how could I determine the resulting pressure AND temperature if they are both unknown after the expansion.

I always thought it related to flow. i.e. Volume increased slowly would mean no temperature change. Volume increased fast would be a large temperature change. Now I think that might only hold true for a system that can absorb ambient heat.

Anyways, thanks for the info. I'll look into that gas law a little more on the internet. If that doesn't work I'll pry open my dusty wallet and get a reference book.

 

[FeX32]

I'm glad you like the ref.

Here is one that I believe you will like more:

http://www.scribd.com/doc/4685776/Thermodynamics

Ch3 has the ideal gas relations.
About your reasoning. What you describe to me seems along the lines of an energy analysis of a control volume. The temperature would relate to the flow if you treat a large mass flow rate into a CV as an energy input into the system or vise versa. (the energy to accelerate the flow would have to come from somewhere).
If there is no energy medium or transfer then stick to the ideal gas law. For example if you were to just let air out of your tire with no energy input then the ideal gas law applies. (as MortenA stated)
Let me know if the link works.

ttyl,


Fe