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    Re: Ford Focus 1999 1.8 endura td Archived Message

    Posted by David Wagstaff on May 26, 2007, 9:41 pm, in reply to "Re: Ford Focus 1999 1.8 endura td"

    Hi Darren,

    I have just read you above response to this question and do not understand your use of the reference to the second law of thermodynamics. From wikipedia,
    [edit] Second law
    Main article: Second law of thermodynamics
    “ There is no process that, operating in a cycle, produces no other effect than the subtraction of a positive amount of heat from a reservoir and the production of an equal amount of work. ”

    This version is the so-called Kelvin-Planck Statement. In a simple manner, the Second Law states that energy systems have a tendency to increase their entropy (heat transformation content) rather than decrease it.

    In simple terms, it is an expression of the fact that over time, differences in temperature, pressure, and density tend to even out in a physical system which is isolated from the outside world. Entropy is a measure of how far along this evening-out process has progressed.

    The entropy of a thermally isolated macroscopic system never decreases (see Maxwell's demon), however a microscopic system may exhibit fluctuations of entropy opposite to that dictated by the Second Law (see Fluctuation Theorem). In fact, the mathematical proof of the Fluctuation Theorem from time-reversible dynamics and the Axiom of Causality, constitutes a proof of the Second Law. In a logical sense the Second Law thus ceases to be a "Law" of Physics and instead becomes a theorem which is valid for large systems or long times.

    Stephen Hawking described this using time as an entropy base. For example, when time moves in a forward direction and one, say, breaks a cup of coffee on the floor, no matter what happens, in our universe, one will never see the cup reform. Cups are breaking all the time, but never reforming. Since the Big Bang, the entropy of the universe has been on the rise, and so the Second Law states that this process will continue to increase.

    Did you in fact mean to refer to fouriers law instead?

    again from wikipedia,

    Heat conduction or Thermal conduction is the spontaneous transfer of thermal energy through matter, from a region of higher temperature to a region of lower temperature, and hence acts to even out temperature differences.

    Conduction is the transfer of energy through matter from particle to particle. It is the transfer and distribution of heat energy from atom to atom within a substance.

    It should be noted that heat can also be transferred by Thermal radiation and/or convection, and often more than one of these processes occur in a particular situation.

    The law of heat conduction, also known as Fourier's law, states that the rate, in time, of heat transfer through a material is proportional to the negative gradient in the temperature and to the area at right angles, to that gradient, through which the heat is flowing:


    where

    Q is the amount of heat transferred,
    t is the time taken,
    k is the material's conductivity. (this generally varies with temperature, but the variation can be small, over a significant range of temperatures, for some common materials.),
    S is the surface through which the heat is flowing,
    T is the temperature.

    David Wagstaff

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