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I Calculation of Pressure in a Cylinder with an orifice on its surface

  1. May 11, 2017 #1
    I want to calculate the pressure profile inside a cylinder whose initial pressure is less than the outside pressure and has a orifice on its surface to flow air through it. Air is a considered as compressible ideal gas and mass flow rate across a orifice is assumed isentropic. Also the temperature is assumed same initially in cylinder and surroundings.

    I am generating the pressure profile inside the cylinder as a function of time using matlab, the method i followed is I took a small delta_t and calculated the massflow rate using available compressed mass flow rate formula and find the net mass flown into the cylinder and I found the new temperature using the energy balance for open system and using ideal gas equation I found the new pressure.

    Now the problem is after some time the pressure inside the cylinder becomes more than the surrounding pressure, Is it possible to have that kind of situation or am I doing something wrong?
    Last edited by a moderator: May 11, 2017
  2. jcsd
  3. May 11, 2017 #2
    Is this a homework problem?
  4. May 11, 2017 #3
    No i am working on ic engines suction modelling i face same kind of problem over there
  5. May 11, 2017 #4


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    Gold Member

    (1) The gas dynamics of engines has been researched in great depth and over many years . You should easily be able to find published information which will tell you exactly how to deal with this type of problem .

    (2) You would find it very instructive to solve your problem analytically before trying to set it up on matlab .

    (3) I really worry about the trend which seems to be becoming almost universal now of people trying to solve problems with matlab , FEA and other types of solver software when they haven't a clue about the science basics or any real idea of how to set up a realistic model of the system they are dealing with .
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