×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

How to determine the thermal conductivity of a sand/aluminum mixture

How to determine the thermal conductivity of a sand/aluminum mixture

How to determine the thermal conductivity of a sand/aluminum mixture

(OP)
Problem:
This should be a very simple problem, I just want to make sure I am doing it correctly. I have a box of sand. I am adding aluminum shavings to it. How do I determine the effective thermal conductivity of the mixture.

Known:
Density of sand and aluminum
Mass of sand and aluminum in box
K values of sand and aluminum

I have seen several methods online how to do this so I want someones expert advice on the correct way to figure out the theoretical effective thermal conductivity of the mixture.

RE: How to determine the thermal conductivity of a sand/aluminum mixture

It's not an area I deal with much, but you've been hanging now for a few days so I'll give it a shot if only to get shot down myself. I'd use a simple rule-of-mixtures approach. The bits of aluminium will conduct well and dry sand particles poorly, so I'd expect the 1/K for the combination 1/Kcomp ~= Vfalu/Kalu + Vfsand/Ksand and Kcomp to be closer to Ksand (after all, if the sand does not conduct heat at all Kcomp will also be zero). So for 25% aluminium by volume (not mass) maybe Kcomp = 1/(0.25/250 + 0.75/0.15) =0.2 W/(m.K). K values from from  http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html .

In 'Introduction to Composite materials Design' Barbero gives an alternative: Kcomp = Ksand * (1+eta*Vfalu)/(1-eta*Vfalu) and eta = (Kalu/Ksand-1)/(Kalu/Ksand+1). For 250 and 0.15 and 25% Vf aluminium this gives Kcomp = 0.25 W/(m.K). (At least, I think it does.)

I tend to trust Barbero, but I must admit this is my simplification of his formula for 2-direction or though-thickness conductivity of a long fibre composite.

My own googling turned up
ftp://ftp.deu.edu.tr/muh/turhan/public_html/papers_Turhan_Coban/Thermal_conductivity_2002.pdf
and
http://wvuscholar.wvu.edu:8881//exlibris/dtl/d3_1/apache_media/L2V4bGlicmlzL2R0bC9kM18xL2FwYWNoZV9tZWRpYS8yMDk0Nw==.pdf
so it looks like it might be quite a bit more complicated and slightly higher Kcomp is possible, but for a reasonable real-world value 'close to the sand plus a bit' is probably good enough as an initial stab, and as usual trial and error with your actual application (whatever it is) is the most practical way forward. If it's important then measuring the Kcomp would seem quite advisable (particularly if the sand can be wet), though it would quite awkward to do well. Let's hope someone with a more practical or aerothermal-type background is prompted to contribute.
 

RE: How to determine the thermal conductivity of a sand/aluminum mixture

viderde (Mechanical)
You also have this posted in heat transfer and thermodynamics engineering.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them.  Old professor

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources