1. Limited time only! Sign up for a free 30min personal 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!

Finding the rate of heat transfer

  1. Sep 14, 2011 #1
    Hi there, I have this complicated question and Im not sure that im converting everything corectly. The question is:
    "For conduction, the rate of heat transfer is given by [itex]\Delta[/itex]Q/[itex]\Delta[/itex]t=-kA([itex]\Delta[/itex]T/[itex]\Delta[/itex]x)

    Data given is:

    k=806 W.m^-1.K^-1
    A=2.53m^2
    [itex]\Delta[/itex]T=-54.6[itex]^{}[/itex]0C
    [itex]\Delta[/itex]x=5.50x10^-3m

    "calculate the rate of energy transfer [itex]\Delta[/itex]Q/[itex]\Delta[/itex]t, and give its correct S.I unit

    I just substituted all of the data into the equation, but didnt know if I had to convert meters^2 into meters?
    so this is what I had:
    [itex]\Delta[/itex]Q/[itex]\Delta[/itex]t= -(806)(2.53)[(-54.6)/(5.50x10^-3)]
    and my answer was 20243496=2.02 x 10^7 W.m^2.K-1(J.s^-1.m^-2.K^-1)- is there a simple unit name for the answer?
     
  2. jcsd
  3. Sep 14, 2011 #2

    cepheid

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    You cannot convert m^2 into m, this is nonsensical.

    As for the final answer, you should end up with something that has dimensions of power (i.e. energy/time). This is clear from looking at the left-hand side: delta Q/delta t. Therefore, your answer should just have units of watts, and if it doesn't, then you've made a mistake.
     
  4. Sep 15, 2011 #3
    oh okay thanks:) but in the working out, is everything right? I mean, converted correctly to get a number of 2.02 x 10^7 ?
     
  5. Jul 22, 2012 #4
    Let us look at the dimensions of the right hand side of your equation

    the thermal conductivity K has the units of W/mK

    A is the area available for heat transfer and thus has a unit of m^2

    dT/dX has the unit of K/m

    so in all, the RHS has the units of W (Joules/Second)

    the LHS must also have the same dimension !!
     
  6. Jul 22, 2012 #5
    As a followup, your substitutions seem to be OK, just that your units do not match up
     
  7. Jul 22, 2012 #6

    cepheid

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Sri_Govind: this thread is 10 months old, and it is highly unlikely that the OP will check it any longer. Resurrecting dead threads for no reason (called "necro-posting") is strongly frowned upon. Don't do it.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Finding the rate of heat transfer
  1. Rate of Heat transfer (Replies: 1)

Loading...