I read in literature that In the case of fully developed simple laminar flow, use of nanofluid will be beneficial if the increase in the viscosity is less than four times of the increase in thermal conductivity according to the following equations
ή / ή0 = 1+ C ή
k/kf = 1+ Ck
C ή/ Ck < 4
where ή and ή0 are the viscosity of the nanofluid and base fluid respectively, k and kf are thermal conductivity of nanofluid and base fluid respectively. C ή and Ck are viscosity and thermal conductivity enhancement coefficients,
this equation is hold good in the case where the viscosity is increasing with filler loading in nanofluids. However , in my case viscosity of nanofluid is lower than that of base fluid so that I am getting a negative value for C ή/ Ck. Of course it is less than 4 and the fluid efficiency is high. However I would like to whether this is acceptable to say that C ή/ Ck ratio is a negative value? Is there is any other method to predict the efficiency of nanofluids in terms of viscosity and thermal conductivity?
Dear Mahesh
I think that this article about ( heat transfer enhancement by using nanofluids and it's effect on viscosity and thermal conductivity ) could help you. I attached this article.
Good Luck
Dear Amir,
This paper mainly discussed about the radial flow behavior of nanofluids. The efficiency is discussed in terms of particle concentration. I would like to know the the relation between viscosity and thermal conductivity for calculating the efficiency. in literature the equation what i have mentioned in my question was used. But in literature they are getting a positive value for the ratio between viscosity and thermal conductivity enhancement coefficients since there an increase in viscosity with increase in particle loading. However in my case, I am getting negative value since the viscosity is decreasing with increase in particle loading where as thermal conductivity is increasing. Od course this will be good property for nanofluid. However, I would like know whether it is scientifically correct if I am presenting a ratio as negative.
Dear Mahesh
It is really an interesting topic !!!, my question is : how can you get a nanofluid viscosity lower than the base fluid ? which base fluid are you using ?
because according to most of the available models, the viscosity should increase with the increase of the volume concentration.
Thanks
Dear Saleh Etaig,
Yes, it is true. I have obtained lower viscosity with nanofluids. My base fluid is Propylene glycol and I am using a nanolayered material synthesized by me as filler. It is my materials property that results in lowering of viscosty
Hi Mahesh
if the viscosity decreases then you may need to check the applicability of the above equation
Thanks
Dear Saleh Etaig,
Is that equation hold good only if the viscosity is increasing? is there any other way we can predict the applicabilty
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