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Thread: Help with easy heat transfer problem

  1. #1 Help with easy heat transfer problem 
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    Sep 2014
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    Here is my problem:
    I got a metal door that separates two rooms at temperatures T1=291K and T3=278K. The dew point in room one is calculated to be 283K (60%RH). I need to insulate the door on the cold side to prevent condensation on the warm side. The area of the door is A=2.6m2 and its thickness is ssteel=0.00635m (1/4in). I found a value for k steel at 43 W/mK on engineering toolbox.

    model:
    q--> ksteel kins
    T1 --www-- T2 --www-- T3

    (T2=285K, 2K over the dew point)
    Here is how I approached the problem (maybe you have input as to where I went wrong):
    I calculated the flow of heat throught the door using Fourier assuming the temperature on the cold side of the door to be higher than dew point:

    q = ksteel (T1-T2)A / ssteel = 123kW

    I then used that to desing the proper insulation kins/sins value using the same equation:

    kins/sins = q / A(T2-T3) = 6772 W/m2K

    Which dosen't make sense since for 1in thick insulation, I would need a material that has kins=172 W/mK. More conductive than the steel door!?


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