Calculate the magnitude of rate of heat flow (in kJ/s = kiloWatts) by conduction

Question

Calculate the magnitude of rate of heat flow (in kJ/s = kiloWatts) by conduction through 2.1 cm thick Aluminum plate with an area of 3.2 m2, if the temperature difference between the two sides is 13.7 oC. Thermal conductivity of Al: 4.9*10-2 (kcal/sec)/(oC m)

We were told to use the equation Q/T = -kA T/x

I used that the first time and believe the negative was the reason i got it wrong

This time i did Q/T = (0.049*4186*3.2*13.7/0.021) Then divide by 1000 to get it into KJ/s or kW this yielded 428kW

If instead of 0.049*4186 i do 4.9*42 (42 is what you get when you go from (kcal/sec)/(oC m) to (J/sec Celcius m) then the answer changes to 430 kW

Thanks for the help

Explanation / Answer

k = .2051 (kJ/s) / (oC m)

Q = k A del T / d

Q = (.2051 x 3.2 x 13.7) / .021

Q = 428.17 kW

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