Dear Vipin Nair

Experimental work will be interesting in such comparison study but also there are some factors need to give special consideration like stability criteria for nanoparticles in basefluids to get reliable empirical correlation especially for thermo-physical properties. also, in numerical side because of several factors such as gravity, friction between the fluid and solid particles and Brownian motion (forces), the phenomenon of Brownian diffusion and also sedimentation may coexist in main flow of nanofluid. this means that the slip velocity between the fluid (continuous phase) and particles (dispersed phase) may be not zero. therefore, it seems that the two phase approach  is better to model the nanofluids than the homogenous single phase model.

Regards.

Experimental data with refrigerant as a base liquid is quite limited.  However, in base liquid water, it is observed to be independent of the material and dependent on concentration, temperature and particle size.  The viscosity increases with concentration and decreases with temperature.  The viscosity increases with reduction in particle size.  

Thank you Prof. Sharma

The viscosity increases with the increase in concentration and decreases with increase in temperature

You are basically dealing with a two-phase system in which there is a dispersed phase that lives inside a suspending medium which acts as a continuous phase.  Spatial arrangement and distribution, agglomeration and de-agglomeration during shear are responsible for changes in viscosity when the concentration is changed. The basic knowledge on such type of systems can be got from the book

Aroon V. Shenoy, Rheology of Filled Polymer Systems, Kluwer Academic Publishers, Netherlands (1999).

There is a chapter on constitutive theories and equations of suspensions where the effects of shape, concentration, dimensions, and size distributions of the particles have been discussed.  Also the entire Chapter 5 titled Preparation of filled polymer systems pages 175-242 is dedicated to the mixing/blending/compounding of fillers into polymer melts.  The sections include Goodness of mixing, Mixing mechanisms, Compounding techniques, Compounding/mixing variables.   In section 5.4, there is a detailed discussion on the compounding /mixing variables that affect the quality of the mix.  Some variables are more sensitive to changes than others. It is important to study and identify these variables and understand their sensitivity so that the compounding /mixing can be carried out under optimum conditions.  Variables affecting compounding operations could be machine variables (mixer type, rotor geometry) or operating variables (mixing time, rotor speed, ram pressure, chamber loading, mixing temperature, order of ingredient addition). The effect of each of these variables for the naonoparticle –matrix combination needs to be understood to find the optimum conditions to achieve the proper level of dispersion and distribution of filler into the matrix, which in turn controls the changes in viscosity with increasing concentration.  You will get the necessary hints on how to go about this by reading Chapter 5 of the book.

Thank you very much Prof. Aroon shenoy. I will get that book as soon as possible. And thanks again for this elaborate answer.

It depends upon the model considered. As per the Brinkman model, Viscosity of nanofluid is inversely proportional to nano particle concentrations. Most of the other models like Einstein model, Brownian model,etc. indicates that viscosity of nanofluid is directly proportional to nano particle concentrations. For further reading, you can refer the Rheology of particle suspensions.

Generally, if you are increasing concentration by volume then your viscosity will increase. However, in a special case if you are increasing concentration by mass but decreasing volume (increasing density of the nanoparticle material), then you may see decrease in viscosity by a small number.

it increases for details see :

Brinkman, H.C., The viscosity of concentrated suspensions and solutions. J. Chem. Phys. 1952; 20: 571–581.

Hello again prof. Aroon shenoy.

I read the book as you said and specifically i read chapter 5.

Thank you for your help.

But your book is based on Non -newtonian pseudoplastic fluids whereas i am dealing with newtonian fluids. Dont you think that the trend for viscosity variations will be different for newtonian and non-newtonian fluids??

mu(nf)= mu(f)/((1-phi)^2.5)

nf: nanofluid

f: fluid

phi: particles concentration

Thank you Prof Lioua

I will refer to your text which you mentioned earlier.

And the expression for viscosity which you have mentioned is for water based nanofluids?

yes for water based nanofuids

viscosity may also vary with shape of your particles, with least viscous when you have Nano particle of circular shape

Thank You Hassan.That was a good piece of information.

Can you please suggest me the reference on the basis of which you are claiming that viscosity will be least with spherical nanoparticles?

Thanks.

This might be helpful to you

Dear Vipin please see the following link, i cannot download it currently

http://www.sciencedirect.com/science/article/pii/S0140700713002028

Thank you very much hassan . i appreciate your help.

And yes,i have free access to sciencedirect here so i will download it.Thank you for the link.

Dear Vipin Nair

Experimental work will be interesting in such comparison study but also there are some factors need to give special consideration like stability criteria for nanoparticles in basefluids to get reliable empirical correlation especially for thermo-physical properties. also, in numerical side because of several factors such as gravity, friction between the fluid and solid particles and Brownian motion (forces), the phenomenon of Brownian diffusion and also sedimentation may coexist in main flow of nanofluid. this means that the slip velocity between the fluid (continuous phase) and particles (dispersed phase) may be not zero. therefore, it seems that the two phase approach  is better to model the nanofluids than the homogenous single phase model.

Regards.

Dear Sir

We should differentiate between nano-fluid and nano-flow. The above explains talking about flow in micro and nano devices (Micro or Nano Flow). Nano fluid as explained before, nano particles added to the a fluid. The modelling and physics is different between Non-Fluid and Nano-Flow...