Please explain what is the negative dynamic viscosity. Is it attainable to attend the negative dynamic viscosity with Al2O3/water Nanofluid and what is the criteria required to get negative dynamic viscosity.
The working condition of nanofluid:
diameter of nano particle- 50 nm
temperature of nanofluid- 50 degree celcius
volume concentration of 4%.
it's my humble request to you to please explain this.
Regards,
Sumit Sharma
Dear Sumit,
It is quite surprising that the viscosity is negative. One could perhaps explain this phenomenon by two things, but I am not sure: 1) . The shear stress would be negative. Either this would add energy to the flow in the direction of the flow violating the second law of thermodynamics or it would reverse the flow direction. In my mind the flow direction would keep reversing and thus the flow would not move at all. 2) The velocity gradient could be negative, i.e. flow would be moving faster on the wall than in the free stream.
With my best regards
Prof. Bachir ACHOUR
Hi Sumit,
My first thought is that your measured negative viscosity is an artefact, possibly from improper sample loading, because as Bachir said, a negative viscosity would imply energy being added to the system.
That said, a "true" negative viscosity has been observed in bacteria suspensions, as under shear, the motion of the bacteria becomes less random and they swim in the direction of the flow, and therefore add to the flow.
https://phys.org/news/2015-07-bacteria-superfluids.html
Ideal fluid is just an assumption...well negative viscosity is a deam
Guys, if you find real negative viscosity, aftwer adding aluminum nano-particles, please tell me how to reach it, we are making progress to increase heat transfer in a glicol-wáter moisture, Thanks
As a matter of interest, what measurement system and geometry are you using?
Looking at your pictures I do not understand why you assume the viscosity to be negative.
An increase of temperature leads to a reduction of viscosity ant to a thinner boundary layer so that the heat transfer is growing up.
When particles are bigger tis modifies the flow structure and can have as result a thicker boundary layer so that heat transfer decreases.
You should explain what brought you to the conclusion that viscosity is "negative".
Hello,
I was trying to find out the dynamic viscosity, thermal conductivity and heat capacity of nanofluid using some correlations and in some cases, where I wanted to calculate these values at the maximum applicability limit of that correlation or equation I was getting negative values.
This is the reason, I asked this question that, Is it possible to get negative value of dynamic viscosity with Al2O3/water nanofluid at some specified conditions.
From your replies I come to know that there is only positive values are applicable.
Thank you for your reply and active support.
Regards,
Sumit Sharma
Hi,
Negative viscosity term is used when viscosity of nanofluids go below viscosity of suspending fluid medium. This phenomena has been observed in Magnetic nanofluids when exposed to high frequency alternating magnetic fields where nanoparticles rotatation induces opposite vorticity in fluid resulting in negative local viscosity.
http://aip.scitation.org/doi/abs/10.1063/1.868108
Can't get the full paper. From the abstract, it is talking about the "additional viscosity"
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