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(Thermo 3D) Power needed to maintain temp

  1. Jul 2, 2015 #1
    If we have a cube full of water and glass walls, with an external environmental temperature of 20 degrees celsius, what is the power required to maintain an internal temperature of 25 degrees celsius?

    Assume sides are 50cm.

    I don't know what to do, I was trying out the P = (kA/L)(Tf-Ti) equation, but due to lack of experience, I don't know how to apply it when you have three mediums (air, glass, and water). Please help?
  2. jcsd
  3. Jul 2, 2015 #2


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    You will probably have to make some assumptions. For example you could assume..

    1) The water is stirred so that the temperature is a uniform 25C.
    2) Likewise the air outside is also stirred so that all the air in contact with the glass is 20C.
    3) The thermal resistance between water and glass is zero.
    4) The thermal resistance between glass and air is zero.

    Then it simplifies to..

    Power = Thermal Resistance of glass * (surface area/thickness of glass) * (Twater - Tair)

    Make sure the units for the thermal resistance of glass match those for the surface area/thickness.
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