Final version of this paper is on Journal of Nanomaterials http://www.hindawi.com/journals/jnm/ ABSTRACT:Aggregation and settling are crucial phenomena that involve particulate systems. For particle sizes of millimetre and above, there are reasonable accurate predicting tools. However for smaller particle sizes, there appears to be a void in knowledge. This paper presents an analytical model to predict the settling rates of nano-to-micro size particulate systems. The model was developed as a combination of modified classical equations and graphical methods. A calculation sequence also is presented. By validation with available experimental data for settling nano-tomicro systems, it was found that the two schemes show order of magnitude agreement. A significant feature of this model is its ability to accommodate non-spherical particles and different fractal dimensions.

This paper presents the most recent review of research articles and patents on thermal conductivity on nanofluids. Larger portion of literature accounts for experimental investigations, which is a sign of the preference for hands-on work by experimentalists. Metallic, non-metallic as well as ceramic nanoparticles of different sizes and shapes were suspended in common heat transfer liquids and their thermal conductivities were measured. In contrast to previous belief, it has now been proven that when the nanoparticle concentration is kept low the degree of enhancement falls reasonably within the boundaries predicted by the effective medium theories. There are strong evidences to suggest that the main mechanisms driving the thermal conductivity behavior are nanoparticle aggregation and the particle Brownian motion in suspension.

No abstract

Nanoparticle suspensions have demonstrated superior heat transfer properties and hence appear to be a strong contender to become next generation coolants. While the presence of particles enhances thermal conductivity, they also contribute to increase the fluid viscosity. The latter will lead to demand more pumping power in convective systems, hence questioning the overall economy of the concept. This paper presents the recently obtained thermal conductivity and rheology data for alumina (Al 2 O 3 ) and titania (TiO 2 ) nanoparticles suspended in ethylene glycol in the temperature interval of 20-90°C and particle concentrations of 0-8wt%. Although the thermal conductivity enhanced by up to 14%, a simultaneous increase in viscosity dampens the net advantage of using nanoparticle suspensions as convective heat transfer fluids.

No abstract