Please confirm answer to thermodynamic question

[pinnacleprouk]

Homework Statement

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.

Homework Equations

dQ/dt = kA(dT/dx)

The Attempt at a Solution

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

T = 55 degree CI'm not sure this is right, any help is much appreciated!

Thanks in advance!

 

[ehild]

Where is warmer? Inside or outside of the greenhouse?

ehild

 

[pinnacleprouk]

It doesn't state!

The exact question is written above.

Thanks!

 

[ehild]

What do you think? What is a greenhouse for?

It was said that the heat loss of the greenhouse is 120 kW. The greenhouse loses energy, heat flows out of it. What is the direction of heat flow? From a warmer place to a colder one or from a cold place to a warm one?


ehild

 

[Je m'appelle]

Heat loss:

[tex]\frac{dQ}{dt} < 0 [/tex]

Heat gain:

[tex]\frac{dQ}{dt} > 0 [/tex]

You must interpret the question and understand that a greenhouse is a structure to regulate and maintain a certain temperature in the inside, usually hotter than the outside environment.

Do your calculations again based on that.