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

AI Thread Summary
To calculate the temperature at different layers within a cavity wall, start with the known temperatures and use the total heat transfer rate formula. For the brick, cork, and wood layers, apply the thermal resistance formula to find the interface temperatures. The total heat transfer rate has been calculated as 416.485 watts. By using the equation Ts2 = Ts1 - qT / Rs12, you can determine the temperatures at the brick/cork and cork/wood interfaces. This method provides a systematic approach to solving the problem.
ingram010
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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

 
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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.
 
Thanks edgepflow

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