Insights into the stability and thermal properties of WSe2-based nanofluids for concentrating solar power prepared by liquid phase exfoliation

Abstract

Nanofluids are considered the new generation of heat transfer fluids thanks to their improved thermophysical properties compared with conventional fluids. However, little research has been performed into the thermal properties, stability and preparation of nanofluids based on two-dimensional nanostructures. In this paper, we discuss the preparation of nanofluids based on 2D-WSe2 nanostructures prepared by liquid phase exfoliation applying two different sources of ultrasound. The base fluid for these nanofluids is a eutectic mixture of biphenyl and diphenyl oxide used as a heat transfer fluid in the parabolic trough collectors of concentrating solar power plants. The 2D-WSe2-based nanofluids were characterized for their stability and thermal properties. Treatment with ultrasonic tip resulted in remarkable improvements in the exfoliation of the nanomaterial and stable nanofluids. At a molecular level, periodic-DFT calculations were performed to understand the stability of the 2D-WSe2-based nanofluids from the perspective of the arrangement of the surfactant molecules around the WSe2 nanosheets. The results suggest that the most favoured interaction with the WSe2 sheets occurs through the hydroxyl terminal group of Triton-X. The hydrogen bond interaction between the H atom of the -OH group of Triton-X and three Se atoms on the surface of the sheet plays a stabilizing role in the system. Thus, the arrangement of the surfactant must facilitate the exfoliation of the WSe2 sheets. Furthermore, WSe2 nanosheets were found to improve the thermal conductivity by up to 39% and the specific heat by up to 9.3%, resulting in an increase in the heat transfer of up to 26%. The results of this study have revealed the great potential of 2D-WSe2 based nanofluids as heat transfer fluids in CSP plants.