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Temperature of Air escaping from tire

  1. Apr 15, 2004 #1
    I have been trying to understand how to calculate the temperature of the air escaping from a blown up tire. I know its adiabatic cooling - but is it as simple as PV = nRT?
    Thanks
     
  2. jcsd
  3. Apr 15, 2004 #2

    chroot

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    An adiabatic expansion goes as:

    [tex]T_i V_i^{\gamma-1} = T_f V_f^{\gamma-1}[/tex]

    where [itex]\gamma \equiv C_p/C_v[/itex].

    - Warren
     
  4. Apr 15, 2004 #3
    In your equation
    1. the i state (T, V) is the state of the air initally, in the tire. I have a tire that has a certain volume (Vi) and is at some temperature (Ti)
    2. the f state is the final state, air coming out of the tire - I understand Tf - what is Vf since the air is escaping to the great outdoors. Is it the amount of air that is escaping - per unit time?????

    Why doesnt velocity of air come into equation
    size of nozzle

    Under expansion, such as though a JT valve, cant I expand air such that in some cases it gives me a decrease in temperature, and in some cases an increase in temperature - something called an inversion line.

    THANKS
     
  5. Apr 15, 2004 #4

    chroot

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    You can easily calculate how much volume the air will occupy once outside the tire (and thus at 1 atm pressure).

    - Warren
     
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