[lammps-users] Thermal conductivity of Ar-Cu nanofluids using fix thermal/conductivity command

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1

Hi, xiaoliang

Did you solve your problem? Is your Ar thermal conductivity still small? I am doing this now, and I got themal conductivity of liquid argon at 100K which is 0.109W/mK similar to the book. I have some concern about your problem.

ziyuan

2010/4/17 Jonathan Lee <jonny5@…623…>

2

Thanks
Now my result for Ar is 0.123W/mK at 85K, which is reasonable.

But I can’t get good results for Ar-Cu nanofluids,now the result is more than 10W/mK, and I think maybe my enthalpy term in heat flux computation is error, so I’m checking

Xiaoliang

— 10年4月28日，周三, shiziyuan <shiziyuan1124@…24…> 写道：

3

So when you calculate your thermal conductivity of argon, did you use fourier law ? heat flux/temperature gradient? If so, when you define temperature gradient, there is a near wall one sigma region, the temperature distribution is different from the bulk region of argon. So if I used the temperature gradient in the bulk region ignoring the near wall effect, my k is reasonable. But if I not, k is much higher cause the near wall temperature made my temperature gradient smaller. This is what my results showed. Do you have similar results?

4

sorry, k should be smaller due to my temperature gradient larger.

2010/4/28 shiziyuan <shiziyuan1124@…24…>

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The results for Ar using both GK method and Muller Plathe method are all reasonable.

When I use compute heat/flux command to compute thermal conductivity of Ar-Cu nanofluids, the results are more than 10W/mK; and when I use fix thermal/conductivity command, i.e., Muller Plathe method, the thermal conductivity of Ar-Cu nanofluids is even less with more volume percentage, about 0.1W/mK.

For Muller Plathe method, I think the wrong result is caused because when execute heat flux, perhaps hot or cold layers is not in liquid state when the average temperature for the whole box is 85K, i.e. , perhaps the cold layers becomes solid state?

For GK method, I think the result is wrong because we have to consider the enthalpy term in heat flux calculation. But I don’t know if the codes used for enthalpy term calculation is right.

Could somebody show me how to add enthalpy term into heat flux calculation(compute_heat_flux.cpp)? thanks

Xiaoliang

— 10年4月28日，周三, shiziyuan <shiziyuan1124@…24…> 写道：

6

Yes, you are right, and I also see the effect and avoided it. The result for Ar is OK, but not for Ar-Cu nanofluids, because the result for Ar-Cu nanofluids is even less than base Ar fluids, which is not the truth in other’s articles and experiments.

Xiaoliang

— 10年4月28日，周三, shiziyuan <shiziyuan1124@…24…> 写道：