How do I calculate the temperature at different layers within a cavity wall?

[ingram010]

Hi all

I have a revision question I am having some trouble with

A cold room has a wall measuring 5.2m by 2.5m. The wall is constructed of 120mm thick brick on the inside, a cork layer 80mm and a 30mm layer ow wood in the outside. the inside temperature is -4ºC and the outside temperature is 70ºC.

The thermal conductivities of the materials are:-

Brick,0.9Wm^-1K^-1, Cork, 0.04Wm^-1K^-1, and wood, 0.17Wm^-1K^-1


The formula for calculating for the rate of heat transfer through all the layers is:-

-Area/ (x1/k1) + (x2/k2) + (x3/k3) x (T1- T2)

so -13/ (0.12/0.9) + (0.08/0.04) + (0.03/0.17) x (-4 - 70) = 416.485 watts.

I am having a problem with the calculating the temperatures at the brick/cork and cork/wood interfaces.

If anyone could help I would be very grateful

Kindest regards

John

The Attempt at a Solution

 

[edgepflow]

Apply:

qT = Ts1 - Ts2 / Rs12

where,

qT = total heat transfer rate (you already calculated).
Ts1 = surface temperature at interface 1
Ts2 = surface temperature at interface 2
Rs12 = thermal resistance between surface 1 & 2 (for example: x1/k1)

So start at the surface with the known temperature (call it surface 1), and figure:

Ts2 = Ts1 - qT / Rs12

and work your way to the other end.

 

[ingram010]

Thanks edgepflow

much appreciated

 

[sourceinfrate]

thank you a lot this was the information i have been searching for last 2 days