Thermodynamic question, please help max points for good answer, thanks in advance!?

Question by Jay: Thermodynamic question, please help max points for good answer, thanks in advance!?
1. The problem statement, all variables and given/known data

The rate of heat loss to the outside through a 10mm-thick glass roof of a green house is 120kW. The length and breadth of the glass material of the roof are 20m and 2m, respectively. Calculate the temperature of the outside if the temperature inside the green-house is 25 degrees C.

Assume thermal conductivity of the glass material is 1.0W/m/degrees C.

Please help as I don’t know where to start.

I know Q = m c delta theta comes into it but don’t know how to apply it to this problem, any help is much appreciated, thanks in advance!

Best answer:

Answer by canic
Heat conduction rate can be expressed as dQ/dt = kA(dT/dx) where k is thermal conductivity of the material in interest (in this case is glass), A is cross-sectional area of the glass and dT/dx is temperate gradient.

we have dQ/dt = 120000W, k = 1W/m/degree C, A = 20mx2m=40m^2 and dT/dx = (T-25degree C)/10mm = (T-25)/0.01m

substitute the value and solve the equation, you shoud get T (temperature of the outside of green house) = 55degree C.

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