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John O | October 2018

Study details how addition of graphene to fluid enhances nanofluid thermal conductivity


By Josh Perry, Editor
jperry@coolingzone.com

 

Three research groups from the Catalan Institute of Nanoscience and Nanotechnology (ICN2) in Barcelona, Spain have published research detailing how the addition of graphene to a solvent results in a nanofluid with enhanced thermal properties.

 


Researchers studied the mechanisms behind enhanced thermal conductivity in nanofluids. (ICN2)

 

According to a report from the institute, this research adds to the knowledge of the mechanisms behind thermal conductivity and heat transfer in nanofluids as well as thermal transport in dynamic systems.

 

The researchers used a graphene-amide nanofluid and studied how different concentrations of graphene impact the thermal performance of the fluid, including its thermal conductivity, heat capacity, sound velocity, and Raman spectra.

 

“Not only do their findings confirm that the presence of graphene impacts positively on all of these properties, including enhancing thermal conductivity by as much as 48% (0.18 wt % of graphene), but they provide considerable insight into the mechanisms explaining why,” the report explained.

 

Researchers were able to rule out several suppositions about how nanofluids work, theories which were based on Brownian motion, and indicated that the mere presence of graphene particles impacted the interactions between molecules in the fluid.

 

“For instance, Raman spectra analysis indicated that the mere presence of tiny amounts of graphene modifies the interactions taking place between all fluid molecules, thereby affecting the vibrational energy of the fluid as a whole,” the report continued. “In addition to this long-range effect, theoretical simulations showed that graphene induces a local parallel orientation of the solvent molecules closest to it, favouring a π-π stacking, as well as a local ordering of the fluid molecules around the graphene.”

 

For more information about nanofluids, read https://www.qats.com/cms/2017/10/04/nanofluids-electronics-cooling-applications.

 

The research was recently published in Nanoscale. The abstract stated:

 

“While the dispersion of nanomaterials is known to be effective in enhancing the thermal conductivity and specific heat capacity of fluids, the mechanisms behind this enhancement remain to be elucidated.

 

“Herein, we report on highly stable, surfactant-free graphene nanofluids, based on N,N-dimethylacetamide (DMAc) and N,N-dimethylformamide (DMF), with enhanced thermal properties. An increase of up to 48% in thermal conductivity and 18% in specific heat capacity was measured. The blue shift of several Raman bands with increasing graphene concentration in DMF indicates that there is a modification in the vibrational energy of the bonds associated with these modes, affecting all the molecules in the liquid.

 

“This result indicates that graphene has the ability to affect solvent molecules at long-range, in terms of vibrational energy. Density functional theory and molecular dynamics simulations were used to gather data on the interaction between graphene and solvent, and to investigate a possible order induced by graphene on the solvent. The simulations showed a parallel orientation of DMF towards graphene, favoring π–π stacking.

 

“Furthermore, a local order of DMF molecules around graphene was observed suggesting that both this special kind of interaction and the induced local order may contribute to the enhancement of the fluid's thermal properties.”

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