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Rate of Temperature Drop

  1. Feb 19, 2013 #1
    1. The problem statement, all variables and given/known data
    A cubic polystyrene box contains a litre of water at 90°C. It is 10cm wide and has a wall thickness of of 5mm. Room temperature is 25°C and the conductivity of polystyrene is 0.033W/m°C.
    What is the rate of temperature drop of the water?

    2. Relevant equations

    P= (KAΔT)/diameter
    E=mCΔT

    3. The attempt at a solution

    P= ((0.033)(0.000001)(65))/(0.005)=0.00429W
    E=(1)(4.2)(65)=273
    t=E/P, therefore:
    t=636363.6364

    ΔT/t=1.0214*10^(-6) °C/s




    Not really sure if i did this right, and i feel really uncomfortable with my answers because
    they're so small. especially the time. I feel i did something wrong with the Area.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Feb 19, 2013 #2

    DrClaude

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    Staff: Mentor

    What is the surface area of the box?
     
  4. Feb 19, 2013 #3
    Your units of thermal conductivity are incorrect. It should be per m2.
     
  5. Feb 19, 2013 #4

    DrClaude

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    Staff: Mentor

    No, W m-1 K-1 is correct.
     
  6. Feb 19, 2013 #5
    Oops. Sorry, you're right. My mistake.

    Chet
     
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