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Heat transfer help please

  1. Apr 29, 2008 #1
    I am working on my first heat transfer design and I have almost all of my data, but I do not know what to do with it.

    I know the following for the material on each side of a wall:
    specific heat
    thermal conductivity

    for the wall in between them I know the following:
    mean surface area
    thermal conductivity

    i understand all about Reynalds, Nusselts, and Prandtl number as well.

    i also know the temperature that both substances will initially be.

    i am trying to figure out how long in time it will take to get one substance (nylon in solid pellet form) to drop from 350 F to 100 F. this nylon will be in a tube with an auger inside moving at a slow rate to transport through the system. On the other side of the wall in the tube will be cold water around 40 F that will be circulating in order to draw the heat out of the nylon.

    if I can figure out the temperature of either side of the wall, I can solve for how long my tube needs to be through lump mass approx method.
    Here are some values I have if I attempt to solve for the wall temp assuming it is convective heat transfer:

    For Nylon
    Cp specific heat capacity 1670 J/kg-K
    k thermal conductivity 0.25 W/m-K
    v velocity 1.524 m/hr (rate of auger)
    p density 560.645 kg/m^3
    R resistance 102317.0565
    u viscosity ?? it is around for 1E+12 kg/m-s for solids but this gives me a "h" that doesnt make sense when i solve for it using the Nusselt number.

    so that didnt seem to work so instead i assume it is conductive heat transfer and use the following:

    k thermal conductivity 0.25 W/m-K
    x thickness 0.889 m
    A Surface Area 17.01674016 m^2
    R resistance 0.208970694

    but again this does not make sense cause i end up getting a temperature on the S.S. wall of less than 41 F when it is next to 350 F, and the water temp on the other side of the wall is 40 F.

    what gives?

    and thanx.
  2. jcsd
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