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 Astrid January 28, 2001 09:58

Temperature in vessel during throttling process

Hi All,

Please comment on what will happen in the following experiment, or give me a literature reference where I can find what will happen.

Imagine an isolated evacuated vessel (P1=0 bar) at ambient temperature. At t=0, I take my magnum rifle (.375 H&H) and shoot a hole in the vessel wall so air (P0=1bar, ambient temperature) will flow in. How will the average temperature evolve during the filling process (neglect the impact of the bullet)? What will the averaged temperature be when P1=P0=1bar?

My thoughts are the following: The physics in the hole have be considered as a throttling process with compressible flow. Regarding the pressure difference, the initial incoming flow will be supersonic and will become subsonic as the pressure difference reduces over time. The transition from super- to subsonic will occur when P1/P0=0.53 (assuming the ideal gas law is valid, Cp/Cv=1.4). The textbooks (for example Fox & McDonald) regarding throttling processes are quite clear in this. However, they hardly describe the occurring processes behind the throttle. They only note that a non-isentropic expansion occur and that shocks are present.

Asking around, I have heard arguments for a rise in average temperature but also arguments for a temperature drop:

-temperature rise: the incoming supersonic flow has a high kinetic energy (1/2u^2) which will heat up the vessel.

-temperature drop: non-isentropic expansion implies a temperature drop (but, don't ask how large the drop is).

Any intelligent suggestion? Or do you have a reference that describes the processes in the vessel?

Thanks, Astrid

 sex00 January 28, 2001 15:15

Re: Temperature in vessel during throttling proces

the average temperture depends on the joule-thompson coeff. of the gas (air in ur case).the arguments regarding expansion process are useless, ultimately thermodynamics has to be satisfied. ur assumption to consider it a throttling process seems plausible but is the enthalpy really constant during the process!depends on the vessel! sex00

 Astrid January 31, 2001 03:34

Re: Temperature in vessel during throttling proces

Thanks for the Joule-Thompson-hint. This is a good pointer in literature search. However, still looking for a worked out example.

Do you recommend any literature reference?

Regards, Astrid

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