hi all
I’m trying to calculate thermal conductivity of Ar-Cu nanofluid.
for that I have written an input script which doesn’t use compute heat/flux and instead it uses a couple of commands so that the entalphy Term in Sarkar formula is included in J calculation.
what I’m not secure about is the auto correlation calculation (J0Jt) procedure, when I plot that, its decays to a negative value and come above zero and after that fluctuates near zero and the Thermal conductivity I reach is smaller than what I expect for it. which I think it is due to this behavior of the auto correlation function.
is there any problem whit my sampling time and correlation length and correlation procedure.
thanks in advance
If you mean the fix ave/correlate command, then it should
do exactly what its doc page describes (though you should
verify that with some simple problem, and dumping out
the info that is used as inputs to fix ave/correlate). I think you
are asking a question that is more about the method/formulas
you are using, rather than a LAMMPS Q.
Steve
Let me add a point to Steve’s comment: in a metallic system, almost all of the thermal conductivity is due to the electrons, not the motion of the atoms. Using LAMMPS to calculate the thermal conductivity using the autocorrelation (J0Jt) is only calculating the portion of the thermal conductivity due to the motion of the atoms. The electronic portion is completely neglected. I think you would get good results for pure Ar or a nanofluid composed of Ar and a non-conductor – but Cu is almost certainly a good electrical conductor, even in very small particles.
I don’t know exactly the coupling between the Ar fluid and the electrons in the metal, but presumably it is in large part a phonon-electron coupling which is well beyond the scope of the models in LAMMPS. Unfortunately, I would think that the details of how heat is transferred from the Ar to the Cu and ice versa is going to dominate the system that you are looking into.
Paul
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