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Adiabatic Availability and Changing States

  1. Aug 25, 2012 #1
    1) What is adiabatic availability?
    2) How can the state of a system change without changing amounts of constituents or without changing parameters?
    3) Does anyone really use the concept of "adiabatic availability" other than Gyftoppoulas and Paolo?
    I am reading the book,
    "Thermodynamics: Foundations and Applications" by Elias P. Gyftopoulas and Gian Paolo Beretta (Dover, 2005).
    The reason that I am working through this book is that I want to have an axiomatic understanding of classical thermodynamics without statistics. This book apparently is an attempt to present thermodynamics in an axiomatic manner. I approve of the approach. However, I am stumbling over the concept of adiabatic availability.
    On page 73 (section 5.3) the book says:
    Adiabatic availability is the largest amount of energy that can be transferred to a weight in a weight process without net changes in the values of amounts of constituents and parameters, <equation 5.8 given to specify "largest amount">.
    I thought the states of the system were uniquely determined by the amounts of constituents and parameters. Then, how can a state change without changing those amounts and parameters?
    The first few illustrations of "adiabatic availability" involve a battery. The battery discharges into an electric motor, doing work. However, the amounts of constituents have to change in order for the battery to discharge.
    Example 5.4 on page 75 is more confusing. It describes the battery with two parameters, energy and charge. When the battery changes state, it changes both parameters. So by definition, it shouldn't be determining the adiabatic availability. Yet, it does.
    A google search seems to indicate that there are a few contradictory versions of the definition of "adiabatic availability" around. So I need help sorting out what the concept really means.
    I would ignore it. However, "adiabatic availability" seems to be a critical concept in this book. I think that I could breeze through the rest of it if I can just understand questions 1 and 2.
     
  2. jcsd
  3. Jan 30, 2013 #2
    The state is uniquely determined by amounts of constituents, parameters AND all properties. You may have confused parameters with properties. While both constituents and parameters are properties, properties have a broader definition: they are attributes that can be measured at any instant of time and are independent of other systems in the environment, other points in time or the measuring device. Parameters, on the other hand, describe the overall effect of the bodies in the environment, e.g. field strength; together with the coordinates of the system's constituents, parameters determine the external forces on the sustem. So two distinct states can have the same constituents and parameters, but they have differing properties of some sort.

    The example of discharging a battery is a bit misleading. Perhaps the author are considering a device that stores charge only without chemical reactions, e.g. a capacitor.
     
    Last edited: Jan 30, 2013
  4. Jan 30, 2013 #3
    Hello Darwin are you referring to the function defined by

    A= U-T0S+P0V
     
  5. Jan 30, 2013 #4
    No. The expression that you wrote is the Gibbs free energy. The Gibbs free energy is not the adiabatic availability.

    The book uses the letter "G" to denote the Gibbs free energy, not the letter "A". The book defines the Gibbs free energy on in Chapter 16.3 on page 249 with equation 16.26 which is,

    G= U-T0S+P0V.

    The adiabatic availability is defined in previous chapters. The adiabatic availability is used to define all the other thermodynamic parameters. Adiabatic availability is apparently more fundamental than the Gibbs free energy, at least in the approach taken by the authors.
     
  6. Jan 30, 2013 #5
    Actually it's not the Gibbs Free Energy, It's more restricted.

    Perhaps I should have been more specific. It refers to systems that are immersed in a constant temperature heat bath T0 and subject to a constant external pressure P0

    I do not have access to your book, so I don't know what you mean so I am trying to translate it into terms I am familiar with.

    Perhaps you could post the definition, if you are still interested.

    My function is called "The Availability Function"

    It is unusual partly because the variables of state do not belong to one system, but are drawn from two conjoined systems.
    This fact allows calculation in the event of irreversible systems.
     
    Last edited: Jan 30, 2013
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