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Technical Briefs

Enhanced Specific Heat of Silica Nanofluid

[+] Author and Article Information
Donghyun Shin

Department of Mechanical Engineering, Texas A&M University, Mail Stop 3123, College Station, TX 77843-3123

Debjyoti Banerjee

Department of Mechanical Engineering, Texas A&M University, Mail Stop 3123, College Station, TX 77843-3123dbanerjee@tamu.edu

J. Heat Transfer 133(2), 024501 (Nov 02, 2010) (4 pages) doi:10.1115/1.4002600 History: Received December 21, 2009; Revised September 02, 2010; Published November 02, 2010; Online November 02, 2010

Silica nanoparticles (1% by weight) were dispersed in a eutectic of lithium carbonate and potassium carbonate (62:38 ratio) to obtain high temperature nanofluids. A differential scanning calorimeter instrument was used to measure the specific heat of the neat molten salt eutectic and after addition of nanoparticles. The specific heat of the nanofluid was enhanced by 19–24%. The measurement uncertainty for the specific heat values in the experiments is estimated to be in the range of 1–5%. These experimental data contradict earlier experimental results reported in the literature. (Notably, the stability of the nanofluid samples was not verified in these studies.) In the present study, the dispersion and stability of the nanoparticles were confirmed by using scanning electron microscopy (SEM). Percolation networks were observed in the SEM image of the nanofluid. Furthermore, no agglomeration of the nanoparticles was observed, as confirmed by transmission electron microscopy. The observed enhancements are suggested to be due to the high specific surface energies that are associated with the high surface area of the nanoparticles per unit volume (or per unit mass).

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Grahic Jump Location
Figure 1

Variation in specific heat of pure eutectic samples and nanofluid samples with temperature obtained from DSC measurements. The specific heat of the eutectic of lithium carbonate and potassium carbonate (62:38) is enhanced by 19–24% on addition of SiO2 nanoparticles (at 1% by weight).

Grahic Jump Location
Figure 2

TEM of silica nanoparticle after mixing with pure eutectic and before thermocycling in the DSC instrument. The nominal size of the nanoparticle in the figure is ∼35 nm.

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Figure 3

TEM of silica nanoparticle after repeated thermocycling of melting and solidification of the nanofluid eutectic. The TEM image shows that the silica nanoparticles are not agglomerated and well dispersed in the pure eutectic after repeated thermal cycles of melting and solidification. The average size of the nanoparticle is ∼35 nm.

Grahic Jump Location
Figure 4

SEM of silica nanoparticles after repeated thermocycling of melting and solidification. The SEM image shows that nanoparticles in the molten salt eutectic are well dispersed. The average size of the nanoparticles is 38.5 nm. A substructure (lighter color) is formed within the eutectic that forms an interconnected network (percolation network). This may enhance the effective thermal properties of the nanofluid due to more efficient heat transfer in the percolation network.

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