A Comprehensive Physical Profile for Aqueous Dispersions of Carbon Derivatives as Solar Working Fluids

Elisa Sani,Luis Lugo,Aldo Dell’Oro,Daniele Di Rosa,Maria Raffaella Martina,Javier P Vallejo,Luca Mercatelli

doi:10.3390/app10020528

Abstract

The application of nanofluids in direct solar absorption, heat transfer or direct solar steam generation entails carrying out a comprehensive study taking into account several physical quantities. Long-term stability, rheological, thermophysical and optical properties of dispersions must be known to assess their potential for envisaged applications. Two low-concentration nanofluids, 0.005 and 0.05 wt%, of sulfonic acid-functionalized and polycarboxylate chemically modified graphene nanoplatelets in water were considered in this work. Elemental analyses of the nanopowders and pH evaluations of the colloids were carried out. The rheological behaviour of dispersions at different temperatures was studied by rotational rheometry. Thermal conductivities were measured by the transient hot wire method and densities by the oscillating U-tube technique. Additionally, a brief report of the optical properties was included to provide a comprehensive physical analysis.

Highlights

Choi and Eastman [1] first proposed that nanometer-sized solid particles could be suspended in conventional heat-transfer fluids to enhance the thermal conductivity
Nanofluids have renewed the research about solar energy applications [3,4], especially in concentrated solar power (CSP) by direct absorption solar collectors (DASCs)
Whereas the external coating of the absorber tube represents its hottest region in the case of conventional parabolic trough collectors (PTCs), the temperature distribution of DASCs is reversed, so that the boundary

Summary

Introduction

Choi and Eastman [1] first proposed that nanometer-sized solid particles could be suspended in conventional heat-transfer fluids to enhance the thermal conductivity. The working principle of DASCs, which were firstly proposed by Minardi and Chuang [5], is the same as conventional parabolic trough collectors (PTCs). These systems converge the sunlight irradiance towards a central absorber tube, where a working fluid is heated and used for power or heat generation. DASCs are equipped with a transparent absorber tube, where a dark fluid flows. This provides a twofold advantage, because the conductive thermal resistance of the coating is removed, and the emittance losses towards the external environment are decreased. Whereas the external coating of the absorber tube represents its hottest region in the case of conventional PTCs, the temperature distribution of DASCs is reversed, so that the boundary

Methods

Results

Conclusion