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Thermal couductivity of granular material

Thermal couductivity of granular material

Thermal couductivity of granular material

(OP)
What would be the relative thermal conductivity of granular material to solid? Roughly? Assuming dry and in air. What would be the effect on grain size or shape.

Specifically I am looking at iron filings to solid iron which I measured to have a relative density of less than 50% I would imagine thermal conductivity to be dramatically reduced.

Any thoughts?

Thanks

RE: Thermal couductivity of granular material

I agree with IRstuff. Contact resistance and contact surface area between grains are factors which take this far beyond the usual practice of determining thermal conductivity. If it's critical to have a fairly accurate model, I suggest setting up your own experiment to test different temp gradients with multiple grain sizes. If you're just looking for a ballpark figure, do a volumetric average of conductivity (to over-estimate k) and/or knock off a percentage to account for contact resistance. I don't have a percentage estimation for contact resistance in that situation, but I'm sure you could cobble something together that would be "close enough." Again, though- run your own experiment if you need an accurate model (and have the time and resources).

RE: Thermal couductivity of granular material

(OP)
Thanks guys

RE: Thermal couductivity of granular material

My comment about conductivity with a granular material is that there will be some settling/consolidation of the granular mat'l and, if in a horizontal plane, the mat'l will pull away from the upper surface (vertical plane will produce hot spot at the top). This will greatly reduce the heat flux in/out of the mat'l. So if one is depending on the granular material to remain in intimate contact with both surfaces, it won't be reliable.

RE: Thermal couductivity of granular material

... so convection may end up dominating, and free convection within a porous media may be important to understand.

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