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Centrifugal compressors, adiabatic compression

  1. Jan 20, 2016 #1
    1. The problem statement, all variables and given/known data
    I am working on creating a spreadsheet where you can input the parameters of an engine at a given rotational speed such as volumetric efficiency, boost pressure, atmospheric pressure and temperature, and compressor efficiency... It's been a very long time since I've done thermodynamics, and have forgotten too much of it to derive all the equations.

    To start with, lets forget about engine speed, volumetric efficiency, and compressor efficiency, and assume perfect adiabatic compression.

    The online calculators I found require the volumes to be known, not the pressures

    2. Relevant equations
    Working with an initial volume of 1 m3 at atmospheric conditions

    P initial = 101,000 pa
    T initial = 300K
    V initial = 1
    Calculate n from ideal gas law: PV = nRT, (n= PV/RT), n = (101000*1)/(8.314*300), n = 40.5

    We know n inital = n final

    Pfinal = 303,000 pa (3:1 pressure ratio)
    Work = ?
    T final =?
    V final =?

    3. The attempt at a solution
    I was trying to work out the solution with the help of this site but I'm not getting too far with it

    When I get there, I will factor in the compressor efficiency as a function of extra work added to the system... So if a perfect system would require 10J, a 50% efficient system would require 20J, raising the temperature and volume, but keeping the pressure the same (since the pressure is what I measure and control)

    Thanks for the help... My mind has turned to mush looking at this for a couple hours
  2. jcsd
  3. Jan 21, 2016 #2


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    I'm a bit confused by your terminology - what type of engine are you trying to develop the spreadsheet for ??
  4. Jan 21, 2016 #3
    Cummins 5.9L diesel. the engine isn't terribly important until you want to know the flow...

    Where I mention V initial I just choose 1 m^3, which would be the volume of air before the turbocharger, and V final is the volume after the turbocharger, They are just a ratio, not an absolute amount.. I know the pressure ratio (3), but am looking for the volumetric ratio which will NOT be 1/3 because of a lot of added heat, and that's where I run into problems
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