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Thread: Rudiger von Massow BSc

  1. #1 Rudiger von Massow BSc 
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    I am a retired metallurgist with experience in corrosion. After retiring I got interested more in thermodynamics, in particular inexact differentials. I would love to explain my view and hope to extend the resulting ideas to physics in general. I live in a small town in Ontario, Canada with no ready contact with a university. I therefore go to a forum to have a knowledgeable conversation.


    Last edited by Rudiger von Massow; July 6th, 2014 at 06:31 PM. Reason: more information
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  3. #2 Internal energy and the volume of a fresh clay vase. 
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    The fact that heat, Q , and work, W, can only determine internal energy, U , as inexact differentials, here represented by 'D', as in: dU = DQ + DW, (2-1)
    which means that they can have any value and only their sum determines the internal energy and their actual value to reach a certain internal energy is path dependant, is sometimes quoted to say that thermodynamics can not provide a relationship between heat and work.
    I like to provide another system which can use inexact differentials, and which may improve the understanding of internal energy: The volume of a vase.
    I shall compare the volume of a trumpet shaped fresh clay vase with internal energy.
    The volume of a fresh clay vase v can be altered by adding rings on the top and altering its height h or by changing the cross-sections of the vase as it exists. We call these changes Dv(height) and Dv(shape). dv = Dv(height) + Dv(shape).(2-2)
    Back to thermodynamics: When I heat a system at constant volume, the heat required to increase the entropy S is dQ = T dS, where S is entropy. Earlier in the heating process the entropy increase required less heat since the temperature T was then lower. The heat content of the system heated at constant volume or no work addition is therefore:
    Q = Integral(0 to S) T dS (2-3)where T changes from 0 to T
    I shall now compare The equations in both systems.
    Thermodynamics------------- Pottery
    dU = DQ + DW (2-4)---------dv = Dv(height) + Dv(shape)(2-5)
    DQ = T dS (2-6)-------------Dv(height = c dh (2-7)
    DW = F dX (2-8)--------------Dv(shape) = Integral(0 to h) (dc) dh (2-9)
    F = Integral(0 to S) (dT/dX) dS (2-10)
    F dX = Integral(0 to S) (dT) dS (2-11)

    Equation (2-6) states that heat addition to a system increases the entropy of the system. The heat requirement of that entropy addition is the temperature of the last entropy added.
    Equation (2-11) states that the addition of mechanical energy to a system increases the heat requirements of the entropy differentials the system already has.

    Thermodynamics claims that this relationship holds only for internal energy. It claims that external energy, energy due to displacement in external force fields, do not hold to this relationship. I disagree.

    Equation (2-11) can not be evaluated, because 1. We do not know the absolute value of entropy and 2. the temperature change can only be calculated as long as the present phase of the system is stable. This means that only a small portion at the high end of the integral can be evaluated. To find out if a certain work addition applies to the relationship, we can mainly determine if the work addition results in a temperature rise at all or if that rise is comparable to the temperature rise due to the same work addition during compression.

    From an SI steam table we can learn by double interpolation that the compression of a gram of steam at 1018.4 degree C from 101 to 100 cc results in a temperature rise of 2.63 degree, requiring a work input of 460 N cm/g. If the gram of steam were instead lifted against gravity by 1 cm, that requires .0098 N cm/g. We would expect that to result in a temperature rise of 2.63*0.0098/460 = 5.6*10 exp(-5) degree C or .56 degree C/ 100 m. It is likely that a small temperature change like that was not measured or, if measured was likely accepted as a measurement error, since classical thermodynamics assumes it to be zero.

    Work of displacement in an electrical or magnetic field can be more easily created by altering the field strength experimentally. Such temperature changes are known as electro - or magneto - caloric effect






    Last edited by Rudiger von Massow; July 15th, 2014 at 03:57 PM. Reason: adding equation numbers and extending
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  4. #3  
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    Another attempt to be understood:
    The concept of 'internal energy' is difficult to understand, since it can only be measured through heat and work exchange where these two inputs are path dependant and are therefore considered 'inexact differentials'.
    I introduce another system, an unfired clay vase, where its volume is a function of inexact inputs. The volume of the vase can be more easily understood than the internal energy of a system.
    The volume is given by:
    where v is volume, h height, and c cross-section

    The internal energy of a system is:


    The volume of the vase can be increased by adding a ring at the top:

    The internal energy can be increased by heat addition: dQ = T dS

    The volume can also be increased by changing the shape:

    The internal energy can also be altered by adding work:

    The differentials of both volume v and internal energy U are inexact, because their values depend on when, in relation to their companion, the differential was applied.
    dv =
    dU =

    This should overcome the misunderstandings associated with inexact differentials.
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  5. #4  
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    Quote Originally Posted by Rudiger von Massow View Post
    Thermodynamics claims that this relationship holds only for internal energy. It claims that external energy, energy due to displacement in external force fields, do not hold to this relationship. I disagree.

    I have no idea about what your talking about but it seems to me that if the Law of Thermodynamics is referring to internal energy then whatever is external is irrelevant. Since when do the laws of nature claim anything? They simply are, no? I know absolutely squat about inexact differentials let alone thermodynamics but for my feeble brain, external and internal are two different things but hey, I could be wrong. And wouldn't you be claiming then that all energy is internal or behaves as internal, there is no external, they're both one and the same, we're all living in a vase inside a vase inside a vase, etc.?
    All that belongs to human understanding, in this deep ignorance and obscurity, is to be skeptical, or at least cautious; and not to admit of any hypothesis, whatsoever; much less, of any which is supported by no appearance of probability...Hume
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    Applying work reversibly on a system, if it is compressing a gas, increases the temperature of the gas. For that reason the work is considered to increase the 'internal energy'. Doing some work on a system against an external field, like replacement of magnetic material in a magnetic field, also increases the temperature. That appears to increase the internal energy as well. work against gravitation requires large replacements to make the possible temperature increase measurable. Thus in that case we can not state that it increases internal or external energy.
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