Dear Ali,

In addition to the paper mentioned by Dr. Borrajo, the attached paper contains useful experimental information about the effect of both size and shape on the thermal conductivity and other properties.

Best Wishes,

Muneer

Hi

Try this reference "Superlattices and Microstructures 52 (2012) 398–415 DOI 10.1016/j.spmi.2012.05.023" could be useful for you

Dear Ali,

In addition to the paper mentioned by Dr. Borrajo, the attached paper contains useful experimental information about the effect of both size and shape on the thermal conductivity and other properties.

Best Wishes,

Muneer

Dear Ali,

In my experience, it is usually found that the size of nanoparticles plays an importante role in heat transfer improvement. it is seen that the increase in nanoparticles size leads to an improvement of the thermal conductivity, but, it is necessary to find out the right proportion which will avoid the clogging problems due to the viscosity effects.

Thanks,

Thank you

Thank you very much for your help Muneer Ismael

Thank you very much for your reply Ruben Borrajo

Thank you very much for your help Anass Bendaraa

Thank you very much for your reply Habibi Samir

Dear @Bendaraa Anass

Do you have any reference about your comment?

The enhancement of convective heat transfer resulting from small nanoparticle diameter (size) this is due to the aggregation of nanoparticles and stronger Brownian motion at smaller nanoparticles diameters, which leads to higher thermal conductivity of nanofluids

Basically, by reducing the particle size, the thermal conductivity of the nanofluids increases. But in some studies, I have seen reduced thermal conductivity by decreasing

size

Plz read this

https://en.wikipedia.org/wiki/Nanofluids_in_solar_collectors#Thermal_conductivity_of_nanofluids

In convective heat transfer, thermal conductivity of nanofluid is due to the Brownian motion of nanoparticles in the base fluid and due to the inter-facial layer of base fluid attached with the nanoparticles. With the increase in size of the nanoparticles Drag force increases, While Brownian force decreases. This reduced Brownian force causes the lesser Brownian motion of larger size nanoparticles hence have the lower thermal conductivity compare to the smaller size particle.

PFA- Effect of particle size on forces(slip mechanism)

Dear Ali,

As we know that the random motion of those nanoparticles within bulk fluids called Brownian motion. Hence, the continuous collision between those particles and molecules of liquids resulting to increase the conductive for those nanofluids. According to Einstein–Stokes equation in literature the Brownian diffusion coefficient in this equation represent the Brownian motion of those nanoparticles so if you see in that equation. the coefficient of Brownian diffusion reciprocal to the diameter of particles and that is mean when the particles diameter increase the Brownian motion decrease resulting in less conduction then low thermal conductivity for those nanofluids. I hop this was quite enough to answer your question. please refer to manuscript titled:

(The effect of alumina/water nanofluid particle size on thermal conductivity)

for Tun-Ping Teng and his group.

My regards

Because of the close proximity of the nanoparticles whether due to the Brownian motion, or the formation of percolating structures, or a combination of the two, the ballistic transport of the phonons across the small gaps between particles could account for a significant increase in thermal conductivity [1].

[1] Michael Saterlie1 , Huseyin Sahin2 , Barkan Kavlicoglu2 , Yanming Liu2 , Olivia Graeve. Particle size effects in the thermal conductivity enhancement of copper-based nanofluids. Nanoscale Research Letters 2011, 6:217

There are plenty of investigations suggest that the thermal conductivity of nanofluid increases with decreasing nanoparticle size. However, it should be noted that few studies showed a reduction in thermal conductivity with decreasing nanoparticle size. So the contradiction in the literature should be considered.

In addition, The Brownian motion can contribute to the thermal conductivity enhancement in two ways, namely, a direct contribution due to motion of nanoparticles that transport heat, and an indirect contribution due to micro-convection of fluid surrounding individual nanoparticles. The thermal diffusivity of the base fluid is usually two or more orders larger than the particle diffusivity, therefore the direct contribution has been shown theoretically to be negligible. Furthermore, indirect contribution of Brownian motion has also been shown a minor effect on thermal conductivity of nanofluids by theoretical analysis. However, Brownian motian could have an important role in producing particle clustering, which could significantly enhance thermal conductivity.

Dear Ali,

According to the logical pieces of evidences have came in the literature (See our paper), the Brownian motion can consider as the major factor in the increment of thermal conductivity of nanofluids and the more decrease in the particle size, the more increase in the thermal conductivity.

Article Influence of cerium oxide nanoparticles on thermal conductiv...

Thank you very much for your reply Sajjad Porgar

Thank you very much for your reply Adnan M Hussein

Thank you very much for your reply Mohammed saad Kamel

Thank you very much for your reply Devendra Yadav

Thank you very much for your reply Dilan S Udawattha

Thank you very much for your reply Ali Taghizadeh

Thank you very much for your reply Kemal Düzkar

Thank you very much for your reply Amina Benabderrahmane

Thermal conductivity of nano-fluid increases with decreasing nano-particle size.