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Flow behaviour of glycolated water suspensions of functionalized graphene nanoplatelets
| Content Provider | Semantic Scholar |
|---|---|
| Author | Gómez-Barreiro, Silvia Vallejo, Javier P. Cabaleiro, David Gracia-Fernández, Carlos Fernández-Seara, José Lugo, Luis |
| Copyright Year | 2016 |
| Abstract | The heat transfer performance of the conventional fluids used in heat exchange processes improves by dispersing nanoparticles with high thermal conductivity, as many researches have shown in the last decades. The heat transfer capability of a fluid depends on several physical properties among which the rheological behavior is very relevant, as we have previously pointed out. In this study, different samples of nanofluids have been analyzed by using a DHR-2 rotational rheometer of TA Instruments with concentric cylinder geometry in the temperature range from (278.15 to 323.15) K. The used base fluids were two different binary mixtures of propylene glycol and water at (10:90)% and (30:70)% mass ratios. Two different mass concentrations (viz. 0.25 and 0.5 wt.%) of graphene nanoplatelets functionalized with sulfonic acid (graphenitHW6) were dispersed in these two base fluids. Firstly, with the goal of checking and calibrating the operation of the rheometer, the viscosity-shear stress curves for pure propylene glycol, Krytox GPL102 oil, and the two base fluids were experimentally determined. A detailed comparative study with those well-known data over the entire range of temperature was stabilized obtaining deviations in viscosity less than 3.5%. Then, the flow curves of the different nanofluid samples were studied at different temperatures to characterize their flow behavior. INTRODUCTION The enhancement of the heat transfer performance has raised great interest during the last century since an increment in the efficiency of thermal facilities could lead to huge savings in their initial and operational costs [1]. Once different approaches such as the use of extended surfaces or the optimization of flow conditions have been extensively investigated, many researchers focus on improving the weak thermal capabilities of most conventional working fluids. A promising way to achieve this aim is by dispersing nano-sized particles with high thermal conductivity in these conventional heat transfer fluids (HTFs). These new nanostructured materials are known as nanofluids and exhibit clear advantages regarding the dispersions of millimeter or micrometer particles such as lower pressure drops or clogging issues [2-3]. Among the different nanoadditives used to design new nanofluids in the past decade, carbon allotropes seem to be those with the most remarkable potential [4]. Within the graphite family, the exceptional mechanical, thermal and electrical properties of graphene (ideally envisaged as a singleatom-thick sheet of hexagonally arranged, sp-bonded carbon atoms tightly packed into a honeycomb lattice) has attracted great attention since this structure was experimentally isolated by Novoselov et al. [5]. Graphene is commercially available in the form of some-layer stacks (normally between 10-100 layers) known as graphene nanoplatelets which combine the properties of single-layer graphene as well as the possibility of being easily and cost-effectively synthesized. Nevertheless, graphene is hydrophobic and it is not possible to obtain dispersions in water for a long time [6-7]. In the case of graphene oxides (GOnPs), their basal planes and sheet edges contain different functional groups and as a consequence the material becomes hydrophilic. The drawback is that the thermal conductivity of graphene oxide is considerably lower than that of pristine graphene since the oxidation process destroys the systematically arranged conjugated structure. Through a reduction of exfoliated graphene oxide, it is possible both to restore the properties of graphene and maintain dispersibility [7]. Different works have shown that the dispersion of nanoparticles remarkably increases the thermal conductivity of conventional HTFs which may lead to improve the heat transfer performance. However, it must also be considered that the addition of nanomaterials can also alter other thermo-physical properties which, in turn, can sometimes offset the thermal conductivity enhancements. Thus, the viscosity (a fundamental property in the Reynolds number) has a strong influence on the flow regime and, consequently, on the heat transfer, for instance. Additionally, an increase in this property can lead to higher pressure drops and, therefore, higher pumping powers [8]. The Newtonian or non-Newtonian nature of the nanofluids 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://repository.up.ac.za/bitstream/handle/2263/61819/GomezBarreiro_Flow_2016.pdf?isAllowed=y&sequence=1 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
