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!

Homework Help: Heat transfer question: Finding the convection coefficient

  1. Feb 28, 2009 #1
    1. The problem statement, all variables and given/known data

    In Betty Crocker's cookbook, it is states that it takes 2h 45 min to roast a 3.2kg rib initially at 4.5 Celsius "rare" in an oven maintained at 163 Celsius. It is recommended that a meat thermometer be used to monitor the booking, and the rib is considered rare done with the thermometer inserted into the center of the thickest part of the meat registers at 60 Celsius. The rib can be treated as a homogeneous spherical object.

    Here are the given variables:
    [tex]\rho[/tex]=1200 kg/m3
    cp=4.1 kJ/kg C
    k=0.45 W/m C
    [tex]\alpha[/tex]=0.91 x 10-7 m2/2
    t = 2hr45min = 9900s
    Ti = 4.5 C
    Tinf = 163 C
    T(0, t) = 60 C


    2. Relevant equations
    The chapter which this goes in has the following equations
    [tex]\theta[/tex]o=(T(0,t) - Tinf) / (Ti - Tinf)=A1e-[tex]\lambda[/tex]12 * [tex]\tau[/tex]

    [tex]\tau[/tex] = [tex]\alpha[/tex] * t / ro2

    Bi = hLc / k

    3. The attempt at a solution
    The book gives us that h = 156.9 W/m2 C

    I've tried -k * dT(ro, 0) / dt = h * (T(ro, 0) - Tinf)

    Where T(ro, 0) = Ti = 4.5 C

    But if I plug in my known value of h that the book gives us, then dT(ro, 0) / dt must be = 55263.7

    I found [tex]\theta[/tex]o = 0.6498, but we cannot get A1 or [tex]\lambda[/tex]1 until we find the Biot number

    I've also tried looking at the Heisler charts, but they have been no use without having both [tex]\tau[/tex] and the Bi number

    There are other questions to this problem but I can figure those out, I just have no idea what to do for this

    Please help!!
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted