1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Heat loss through conduction.

  1. Feb 9, 2016 #1
    Usually it is said that loss of heat through a chunk of material because of conduction is proportional to difference in temperature and inversely proportional to thickness of material.
    E.g. if I got a wall to ΔQ = K*S*ΔT/D.
    where ΔQ - is energy flow through material. K - constant characteristic to material , S - area through which energy flow happens, ΔT difference in temperature on both sides of material ( in direction of flow) and D - material thickness in direction of the flow.

    What I don't understand, is why in case when the process has stabilised ( temperatures are constant on both side of material for a long time) D works to diminish the flow. I know that it is common sense, but I don't understand physics of this process. Can someone explain what happens it terms of atomic or molecular model?
    Also, lets say we got a bar of homogenise material which is heated on one side. how looks distribution of temperature through a bar of material as function of time and distance from the point where heat is applied.
     
  2. jcsd
  3. Feb 9, 2016 #2
    At steady state, the graph of temperature from T1 to T2 through distance D is a straight line of constant slope.
     
  4. Feb 9, 2016 #3
    Yes, but before the system stabilised? During this period distribution of temperature as function of time and distance from 0 can be different.
     
  5. Feb 9, 2016 #4

    Nidum

    User Avatar
    Science Advisor
    Gold Member

    Think of the block as a series of layers stacked together . First layer has to heat up before it can heat next layer etc sequentially through the total thickness .

    The layers don't just conduct heat they store it as well so it takes time for their temperatures to rise .

    May be better to put this in mathematical form rather than descriptive . The mathematics for one dimensional heat conduction is relatively easy to understand .
     
    Last edited: Feb 9, 2016
  6. Feb 9, 2016 #5

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    Have a look at this Excel Animation. It shows the way the temperature varies in time over a 2D area when a hot object appears in it. It's a diffusion model.
     
  7. Feb 10, 2016 #6
    Hello,
    There are two questions in my original e-mail:
    The second one - about temperature distribution as function of time and distance from heat source is more or less clear, but if someone can recommend where I can read about relevant math it would be great.
    The first question actually is more of a problem: on one hand common sense tells that thicker insulation diminishes heat flow from high temperature area to cool area,
    on the other hand, once the system reaches equilibrium ( constant temperature difference on both sides of insulator) it seams to me that insulator thickness shouldn't have any effect on amount of energy loss.
    I try a very simplified model - a long bar of homogeneous material with constant cross section ( 1 dimensional problem) with constant temperature difference on both sides . Once equilibrium is reached insulator doesn't store heat anymore. So taking as example the above model - series of layers stacked together, why 10 or 1000 of layers will conduct less heat then a single one.
    My feeling is that there is something that plays a role of resistance in electrical current transfer of flued transfer through a pipe, but in those cases there is energy loss through heat, which doesn't haven here,
     
  8. Feb 10, 2016 #7

    Nidum

    User Avatar
    Science Advisor
    Gold Member

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Heat loss through conduction.
  1. Heat conduction (Replies: 4)

  2. Heat loss calculation (Replies: 3)

  3. Heat loss and mass (Replies: 8)

Loading...