I am measuring the thermal conductivity of CuO/EG nanofluids experimentally. At low volume concentration of 1 and 2%, thermal enhancements are very high. At 3 and 4% vol. conc., thermal enhancements drop significantly. What are the possible reasons.
As we know nanoparticles form clusters. At higher concentrations they may form relatively larger clusters compared to lower concentrations. and as per we concern nanoparticles Brownian motion theory , the Brownian motion effect reduces at higher particle size. Therefore, thermal conductivity enhancement may drop.
Hello Ezekwem,
I agree with Dilip.
High particle concentrations in the nanofluid will lead to high particle agglomeration which not only reduces the Brownian velocity of the particles but also results in settling down of particles. So these two factors hinder the thermal conductivity enhancements.
Moreover, viscosity of the nanofluid increases non-linearly with increase in particle concentration.Therefore,it is better to keep a low concentration of nanoparticles in the fluid.
Thank you
Hello Ezekwem Chidozie,
There are many reasons which are responsible for decrease in thermal conductivity enhancement at higher nanoparticle concentrations. The main reason is stability as nanoparticles cluster formation starts at higher concentration which leads to decline the thermal conductivity. Please read this.
http://www.tandfonline.com/doi/abs/10.1080/02726351.2016.1180335
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