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Aerospace How mass flow and pressure ratio is related in case of a Gas Turbine

  1. Jun 1, 2017 #1

    As per my observation and experience, when we use evaporative cooler to cool the inlet air to the gas turbine, the compressor discharge pressure (i.e PCD or P3) rises. As, the temp. of the inlet air drops and the mass flow increases due to the increase in density, I believe the discharge pressure of the compressor also rises.

    However, as per the performance characteristic curve of the compressor, the pressure ratio is inversely proportional to the mass flow.

    Can please someone help me understand this
  2. jcsd
  3. Jun 4, 2017 #2
    Yes,your relation is absolutely right.
    The conservation of mass (continuity) tells us that the mass flow rate mdot through a tube is a constant and equal to the product of the density r, velocity V, and flow area A:

    Eq #1:

    mdot = r * V * A
  4. Jun 5, 2017 #3
    I am interested in knowing that when the mass flow across the compressor rises what happen to the pressure ratio ?
  5. Jun 5, 2017 #4


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    Could you provide a bit more context ? You seem to know what you are describing, but we see only loose fragments.
  6. Jun 5, 2017 #5
    If you provide more information and facts about your query,I am sure I will be able to help you out.
    (By giving mathematical evidences).
  7. Jun 5, 2017 #6
    It is a land based application of an aeroderivative gas turbine (twin shaft). Gas turbine is driving a centrifugal compressor to compress a natural gas to a certain pressure. We have installed an evaporative cooler to cool the inlet air to the gas turbine. Now, as the inlet air is cooled down, the air got dry, and the density of the air increases and so is the mass flow. As this happens, I observe that the pressure ratio across the integral compressor (gas generator) of the gas turbine increases. I want to understand why this is so that pressure ratio increases with the increase in mass flow ?

    I hope I am pretty clear this time. :)

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