1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

(Thermal Conductivity Question) Need Help!

  1. Jan 19, 2009 #1
    1. The problem statement, all variables and given/known data

    1) The inner and outer surfaces of a glass window of area 2.5 m2 are at 22 ºC and 0 ºC respectively. What is the heat lost in 1 second if the glass is 5mm thick and has a thermal conductivity of 1.1 Wm^-1K^-1 ?

    2) The same sheet of glass as described in the [above Question] is used as a window in a room at 23 ºC when the general outside temperature is -14 ºC. If the inner and outer heat transfer coefficients are both 17.0 Wm^-2K^-1, what is the temperature of the outside surface of the glass?

    Can Anyone help me solve these two questions, Please? (with the formula used)

    :)
     
  2. jcsd
  3. Jan 20, 2009 #2

    CompuChip

    User Avatar
    Science Advisor
    Homework Helper

    Hi MoZeS, welcome to PF.

    You have given the thermal conductivity and note that there is a unit: W/(m K)
    So what does the thermal conductivity express?
     
  4. Jan 20, 2009 #3
    dQ/dt=kA(d theta/dx)
    given,A=2.5m^2, x=5mm, k=1.1 Wm^-1K^-1
    dQ/dt=kA(final temp-initial temp.)/x
    =(1.1)(2.5)(22)/(5x10^-3)
    =1.21x10^4W
    Q=1.21x10^4J since, Q/t=1.21x10^4W
    Q=1.21x10^4W/1s
    therefore W/s = J
    part 2, try on ur own ...
    is same formulae...
    dQ/dt=1.21x10^4W
    so, subst. in the equation and find the final temp.
     
  5. Jan 20, 2009 #4

    CompuChip

    User Avatar
    Science Advisor
    Homework Helper

    Welcome to PF lyming.
    Please note that we don't give out complete solutions here at PF. Moreover, I don't really see what formula you are using (what is theta?) and how you are getting Q from dQ/dt. Also, there must be some mathematical errors, because I happen to know that W = J / s while you write W/s = J.

    Finally, I think no looked up formula is needed at all and one can infer the answer by simply looking at the units of the given conductivity.
     
  6. May 14, 2010 #5
    I see this one's been dead a while, but if someone want to help me out here...
    I get the first part, but I'm struggling on the second one.
    Do I still need to use the 1 second? And how to do I change the heat flow to temperature? Or is there a delta Temp used to solve this part?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: (Thermal Conductivity Question) Need Help!
  1. Thermal Conduction (Replies: 1)

  2. Thermal Conductivity (Replies: 2)

  3. Thermal conductivity (Replies: 0)

Loading...