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Convection heat transfer

  1. Jul 17, 2015 #1
    Hello, my problem is the following:

    I have an iron bar, which can be heated by convection through an electric cable with power Q.
    I want to know the temperature of the iron bar after 1 hour has passed, both in the case when the power is
    turned on and when it is off (Q=0).

    the input parameters are the temperature of the iron bar at instant zero and the environmente temperature,
    the output is the new temperature of the iron bar after 1 hour.

    Thank you.
    Last edited: Jul 17, 2015
  2. jcsd
  3. Jul 17, 2015 #2
  4. Jul 17, 2015 #3
    no it is not an homework problem, I have a solution which is

    T_final = F + Q/(u*A*L)

    where F is the formula that updates the temperature and it works quite well.
    The term


    represents the increment of temperature due to the electric cable, where Q is the power, u the coefficient of convective exchange, A the area of the iron bar and L the length of the cable. I want to check the correctness of the term Q/(u*A*L), if you may help me.
  5. Jul 19, 2015 #4
    I have an iron bar not insulated, of length 6 meters, heigth 28 cm and width 4 cm, hence the area is 1.68 m^2 and the mass is 529.13 Kg.
    The heat capacity of iron is 450 J/Kg*K.
    The thermal conductivity of iron is 0.023 W/m*K.
    The thermal expansion coefficient is 0.0037 C^-1.
    The density of air is 1.30 Kg/m^3.
    The dynamic viscosity of air is 17.157 * 10^-6 Pa*sec.
    I assume that at time zero the internal temperature of the iron bar is 5 degrees Celsius, the external temperature is -4 degrees Celsius (the bar is not insulated).
    The power Q that pass through the cable is 22,5 KWatt, and the length of the cable is 14 meters, the heat transfer between the cable and the iron bar is by convection.

    I need to know after 1 hour has passed the new internal temperature of the iron bar.

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