Gas Thermal Conductivity

[2rmengineering]

Helium has a thermal conductivity 5times that of air (air is .0257 W/(mK) where helium is .1513 W/(mK)). If I have a container filled with 90% air and 10% helium, will the thermal conductivity be dependent on the ratio too?

Reference my heat previous thread, below:

http://www.eng-tips.com/viewthread.cfm?qid=299758&page=1

 

[vpl]

Since you've chosen mechanical as your engineering specialty, surely you've taken some thermodynamics classes?



Patricia Lougheed

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[hacksaw]

you can use Kay's rule to estimate the thermal conductivity
based on the mole fraction of your constituents, but remeber the approximation is only good at low pressures and well above the critcal temperatures

 

[Tmoose]

I think With gases between panels at least, at some point the convective loops in the gas result in greater heat flow than the gas conductivity would predict.
Thus, multi-pane window systems suddenly went from 2+ inch airspaces to some thing like 3/16".
Similarly, A long time ago rule of thumb for heat sink fins in still air was at least 1/4 inch between fins to encourage useful amounts of convection.

 

[chicopee]

I just downloaded this article front page relating to your post
NASA TECHNICAL NOTE
APPROXIMATE FORMULAS FOR VISCOSITY AND
THERMAL CONDUCTIVITY OF GAS MIXTURES
by Richurd S. Brokaw
Lewis Reseurch Center
CZeveZund, Ohio
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON, D. C. NOVEMBER 1964

You can also refer to Kent"Power" 12thedition, pg 3-15 on method to appx such value K=(b)x(mu)x(Cv). Determining the specific heat (Cv) of the mixture is well documented and I would think that you can approximate the viscocity =(mu) of the mixture the same way. The values of constant "b" from 1.31 for complex gases, 1.70 for triatomic gases, 1.90 for diatomic gases, 2.44 for monatomic gases.

 

[btrueblood]

What temperature are you trying to quench to? If only about 200-300 F, look at using low-temp. steam, k is even more than He.

 

[vpl]

I think this relates to his other question about refilling helium bottles.

Patricia Lougheed

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[2rmengineering]

US Patent #5173124 states that the heat transfer coefficient for 80% helium and 20% argon is better than 100% helium. See Figure 5 in:

http://www.google.com/patents?id=59kjAAAAEBAJ&printsec=abstract&source=gbs_overview_r&cad=0.

The project is to be similar to HIP operation, but much faster. I need 10Atm of pressure. I would normally use 10Atm of air, but the heat transfer rate of air is low. I could use 100% helium, but helium is expensive. So, the ideal situation would be to get the heat transfer properties of helium and the low cost and pressure from air. So 90% air and 10% helium would be ideal.

If I could recycle the helium for low cost, then there is no need for air. Any options or suggestions would be nice!