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Lava conductive cooling

  • Thread starter roam
  • Start date
  • #1
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Homework Statement



A lava beds cool very slowly, remaining warm for years. Calculate the rate of heat conduction per square metre through a 30 m thickness of rhyolite, if the surface is 400 degrees celcius and its interior side is at 3100 degrees celcius. The thermal conductivity of rhyolite =0.84 Wm^-1 degrees celcius^-1.

Answer must be 75.6 W/m^2


Homework Equations



[tex]P=kA \left| \frac{dT}{dx}\right|[/tex]

(The rate is P, k is thermal conductivity, dT/dx is temprature gradient)

The Attempt at a Solution



dT/dx = 3100-400 = 2700

[tex]0.84 \times 30 \times(2700) = 68040[/tex]

Can anyone show me the problem? ...because the right answer is 75.6!
 

Answers and Replies

  • #2
ideasrule
Homework Helper
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Why are you multiplying by 30 instead of dividing? dT/dx is 2700/30.
 
  • #3
1,266
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Why are you multiplying by 30 instead of dividing? dT/dx is 2700/30.
Yes, but I need a number for area A!
 
  • #4
1,266
11
Oh, never mind I get it. THANKS!
 

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