# Need Help with Thermo Energy Transfer problem

1. Sep 12, 2008

### jcamp11

A 0.2-m-thick plane wall is constructed of concrete. At steady state the energy transfer rate by conduction through a 1-m^2 area of the wall is 0.15 kW. If the temperature distibution is linear through the wall, what is the temperature difference across the wall, in K?

i dont even know where to start, anything will help...

2. Sep 12, 2008

### jcamp11

I have been doing some work on this.. and i have came up with an answer, im pretty sure its not right though..

Using Fourier's law:

Qx= -kA[T2-T1/L]

we know that the Qx is .15kW per 1 m^2, and the thickness of the concrete plane is .2 m

If .15kW of energy enter 1.0 m^2, then only .03 kW enter the area of .2 m??

right now i have .03kW= -k(T2-T1/ .2m)

im stuck..

3. Sep 12, 2008

### Topher925

Why is this? I don't think you understand the concept of "heat flux" which you represent as Qx. Heat flux is the rate of heat transferred given an area. In math form thats

q" = $$\frac{dQ}{dt}$$ = Qx

So if you have 0.15kw of energy being transferred over 1m^2 of area, what is your heat flux going to be?

You are also going to need to look up the transfer coefficient (k) for concrete. I imagine this is in your book somewhere.