dirt properties

[jaysihn]

I am looking for the thermal conductivity of Dirt and am having no success. I just want a ball park number for dirt/dust.

anyone have any ideas?

 

[CRG]

I do not know of any ballpark figures for the thermal conductivity of dirt because the properties are highly dependent on moisture content, density, compaction, and air space within the dirt. I would think that to even get a ballpark number, the moisture content would be required.

 

[jaysihn]

I agree, that makes sense.

The application is I am wondering what kind of effect a thin layer of dirt or dust will have on the thermal resistance of 2 plates that are sandwiched together under pressure (to be determined) It will see fairly high temperatures so I would think the moisture content would be quite low after the plates are heated. Heat needs to go from the outside of one plate to the outside of the other.

What other things should I consider

 

[amorrison]

Check out "thermal contact resistance" in a heat transfer test.

J. P. Holman "Heat Transfer" -7th edition - shows in a table that surface roughness, temperature and pressure are important variables.

There are some references to research papers also.

The "air" space created by the surface roughness and dust - as a combination - will be a very important factor.
As metal to metal pressure/force is increased there will be more metal to metal surface contact, the dust thickness will be decreased by crushing and the "gas" thickness (=insulation effect)will be decreased.

 

[amorrison]

Try googling

"thermal contact resistance" -heatsink

also.