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Heat transfer in pond

  1. Mar 18, 2012 #1
    1. The problem statement, all variables and given/known data
    The temperature at the bottom of a pond of depth L IS 4°C. The temperature of the air , just above the layer of ice frozen at the pond surface is -2°C.
    THE THERMAL CONDUCTIVITY OF ICE IS THREE TIMES THAT OF WATER

    The thickness(X) of the frozen layer of ice must be-



    2. Relevant equations
    Q= k*A*dQ/dx


    3. The attempt at a solution
    K(ice)A(T-{-2})/X = K(WATER)A(4-T)/L where T is the temp. just below the ice layer
    3K(WATER)A(T-{-2})/X = K(WATER)A(4-T)/L
    FROM WHERE TO GET THE ANOTHER EQUATION
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Mar 18, 2012 #2

    gneill

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    Staff: Mentor

    If the pond is in equilibrium so that the ice is neither growing nor melting, what can you say about the temperature at the water/ice interface?
     
  4. Mar 18, 2012 #3
    So, how to solve this problem ?
     
  5. Mar 18, 2012 #4

    gneill

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    Staff: Mentor

    Assume equilibrium. Write equations for heat flow and temperature that reflect the equilibrium conditions (which in this case are particular temperatures that need to be met at various places).

    You can probably ignore the area aspect of the problem and just assume a linear dependence on the thickness for the heat resistance of the materials; since you won't need any particular values for the heat resistivities, just call the resistivity of ice ##\rho## so that a layer of thickness T will have heat resistance ##R_{ice} = \rho##T. What then would be the resistivity of water, and its resistance for a layer W thick?
     
  6. Mar 18, 2012 #5
    I think it is safe to take the temperature at the ice/water junction to be 0 celcius
    The equation you need is
    dQ/dT = kA(dθ/dx)
     
    Last edited: Mar 18, 2012
  7. Mar 19, 2012 #6
    How can we take the temp. at the junction to be 0°C

    But by the ans. given in the booklet , the temp. at the junction is coming -1°C.
     
  8. Mar 19, 2012 #7

    gneill

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    Staff: Mentor

    If the temperature at the water/ice interface was less than the freezing point for water then the ice would still be growing. If the temperature at the water/ice interface was greater than the freezing point for water then the ice would still be melting. Neither of those situations would be an equilibrium condition.
     
  9. Mar 19, 2012 #8
    THANKS to you all for the help..
     
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