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OTTO cyle

  1. Nov 21, 2009 #1
    I have a general question about otto cycle. If we heat a gas with constant volume its temperature rise according to PV=mRT. However during Isentropic compression(delta Q and delta S is zero), the volume is becoming less and pressure is increasing but i don't know why the temperature should increase during this process. According to the above equation the temperature can increase or decrease but i don't know why it always increases..
  2. jcsd
  3. Nov 21, 2009 #2


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    Homework Helper

    The internal energy of an ideal gas is proportional to its temperature. The change of internal energy in a process is

    [tex]\Delta U = Q + W [/tex]

    where Q is the heat gained from the surroundings and W is the work of the external forces.
    When Q =0, a positive external work (compression) will increase the internal energy, so the temperature will increase, too.

  4. Nov 21, 2009 #3
    Thanks alot... failed to think from internal energy's perspective.
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