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Originally Posted by Cathar
Maybe my problem is in the interpretation of "spreading resistance".
The way I see it is this:
1-D resistance is as Les defined, travelling a fixed distance through some material where the (flat) convectional surface area is the same size as the heated patch. Heat doesn't move sideways in any fashion. There's no x-y movement of the heat. It only moves in one dimension, ala 1-D resistance.
Spreading resistance is naturally going to be the cost of moving heat in the other 2 dimensions when the (flat) convectional patch is larger than the heat flux going in. I mean, it's more difficult to move heat through the initial 10x10mm section of copper, than it is to move that same heat through the full size of the convectional patch (assuming the convectional patch is larger than the heat flux entry patch).
I utterly fail to see how given a 1D resistance as how it is being defined can ever result in a spreading resistance of zero when the heat patch and the convectional patch are of mismatched sizes.
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Was dealing with a 1-D case.
When 3-D, the Spreading Resistance is the difference between the 3-D resistances
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Originally Posted by Cathar
Yeah - I did simulate on my little proggy a stepped pyramid kinda deal for the block. i.e. imagine an Aztec pyramid shape. Not quite a sphere, but for these sorts of dimensions - close enough.
It did work out pretty well, being about 2C behind the White Water (from memory) .............................................
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Possibly misleading without the stipulation of h