Convection and Gravity

Discussion in 'Physics' started by Ratch, Mar 11, 2009.

  1. Ratch

    Thread Starter New Member

    Mar 20, 2007
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    jpanhalt,

    From: Thermodynamics, an Engineering Approach, Yunus A. Cengel and Michael A. Boles, Second Edition, p. 96

    "Convection is the mode of energy transfer between a solid surface and the adjacent liquid or gas which is in motion, and it involves the combined effects of conduction and fluid motion. ... In the absence of fluid motion, heat transfer between a solid surface and the adjacent fluid is by pure conduction."

    From: Random House Webster's Unabridged Dictionary

    con·vec·tion n.
    1. Physics. the transfer of heat by the circulation or movement of the heated parts of a liquid or gas.

    e·lec·tro·pho·re·sis n.
    1. Also called cataphoresis. Physical Chem. the motion of colloidal particles suspended in a fluid medium, due to the influence of an electric field on the medium.

    Now, would you be so good as to explain why a definition from a good thermodynamics textbook and a dictionary is not correct. And if you please, also explain what electrophoresis has to do with the definition of convection.

    Ratch
     
    Last edited: Mar 12, 2009
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Wrong. That is not convection.

    The requirement of gravity (or acceleration by any means) for convection was studied long ago. A researcher named Lunar demonstrated practical electrophoretic separations about 40 years ago in which he largely negated the adverse effects of convection by having the supporting fluid rotate in a sheet to simulate zero gravity over time. The process was later demonstrated in real microgravity on the shuttle.

    John
     
    Last edited by a moderator: Mar 11, 2009
  3. Ratch

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    jpanhalt,

    I also said that induced air flow can support convection. And no air flow can still support conduction. A hard vacuum stops both convection and conduction.

    Ratch
     
    Last edited by a moderator: Mar 11, 2009
  4. jpanhalt

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    Ratch,
    I agree on the conduction part, but you said convection. Partitioning based on density requires gravity.

    John
     
    Last edited by a moderator: Mar 11, 2009
  5. Ratch

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    studiot,

    Newton's Law of Cooling if for convection, and Fourier's Law of Cooling is for conduction. So neither of those methods work in a isolated vacuum, such as outer space or a vacuum chamber. Gotta go with radiation if you want to dissipate heat energy in those places.

    Ratch
     
    Last edited by a moderator: Mar 11, 2009
  6. Ratch

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    jpanhalt,

    From a textbook on thermodynamics. Convection is a type of conduction.

    Well, conduction still works if air is present. A fan can be used to support convection in weightlessness.

    Ratch
     
    Last edited by a moderator: Mar 11, 2009
  7. jpanhalt

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    Where did you find that Newton's Law was for convection only?

    Convection does not occur in zero gravity.

    John
     
    Last edited by a moderator: Mar 11, 2009
  8. thingmaker3

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    To minimize distraction from the original topic, I have moved the debate into it's own arena. Please enjoy your debate - I'm certainly enjoying it.

    Please also accept my apology for any inconvenience resulting from the loss and subsequent restoration of these posts.
     
  9. jpanhalt

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    Glad you agree on using a dictionary to define words. Here's what the OED has to say about it:

    As for the example in which I referred to the effects of convection in electrophoresis and a demonstration that in effectively zero gravity it does not occur, I think the context is clear.

    John
     
  10. Ratch

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    Mar 20, 2007
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    jpanhalt,

    Not just a dictionary, but a good thermodynamics text book also. Text books are usually better and more complete than dictionaries, especially technical with terms.

    Rather incomplete, don't you think? Doesn't say anything about forced air convection. True, one does not get natural convection without weight, but that is not the only type of convection.


    Since electrophoresis is an application of an electric field, it works just fine in weightless conditions, I think you need to explain better how convection ties into that method.

    Ratch
     
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