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Heat transfer through wall - Insulation thickness

by klopjob
Tags: heat, insulation, thickness, transfer, wall
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klopjob
#1
Dec16-11, 05:24 AM
P: 2
Alright, chemistry student here. No previous experience with these types of problems. Doing an interdisciplinary student project where we have to insulate a thin aluminum wall.

http://i.imgur.com/8ztNq.gif

We have a x=5mm thin aluminium wall used for dividing two air flows. T1=308 K and T2=283 K. Aluminium has a thermal conductivity of k=220 W/m,K. Assuming the wall areas are 1 m2 we can use the equation

1/U=(1/h1)+(x/k)+(1/h2)

to determine the overall heat transfer coefficient U [W/m2K].

What are some reasonable values for the heat transfer coefficients h1 and h2? If we have these values we can calculate the heat flow Q [W] through the wall. For instance, using h1=60 W/m2K and h2=40 W/m2K, we get Q=U*dT=600 W.
Now say we want to put a thermal barrier coating on the hot side of the wall so that the wall temperature, Tw1, goes up by 10 K. The coating has a very low thermal conductivity of k=0.02 W/m,K. Is there a way to estimate how thick the coating needs to be to achieve this? Is there enough info to solve this, or do we need more numbers?
Does the heat transfer coefficient h1 change when we apply an insulation layer? Any help or tips would be greatly appreciated!
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rsk2mc
#2
Dec19-11, 08:44 PM
P: 15
What type of heat transfer are you doing? Conduction,convection,radiation this is going to determine the equation. I'm not sure you are using the correct equation as I do nit know what type of heat xfer it is
Travis_King
#3
Dec20-11, 07:47 AM
P: 820
Thermal Conduction

I haven't done much with insulation, and I don't really feel like crunching numbers, but you'll either have to pick a desired delta T (or Q or whatever you want) or you'll have to do iterations until you are satisfied. Excel worksheets usually work pretty well for stuff like this.


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