Graphene Nanofluids as Thermal Management Materials: Molecular Dynamics Study on Orientation and Temperature Effects

Abstract

The dispersion of graphene nanoparticles in a fluid can enhance the thermophysical properties of the base liquid. The physics behind such a phenomenon has yet to be uncovered in the community. In this work, thermal transport in a graphene–water mixture is studied by classical molecular dynamics simulations. Several factors including orientation angle, curvature, thermal rectification, temperature, and van der Waals interaction are investigated, and special attention is paid to the effect on thermal conductance across graphene–water interfaces. It is found that thermal conductance increases from 13.92 to 26.70 MW/m2 K as the orientation angle is increased from 0° to 90°. When the curved graphene is introduced by altering the length to width ratio from 1.0 to 1.8, the thermal conductance is elevated. However, as the length to width ratio exceeds 1.8, such a trend does not continue due to the variation of the intrinsic thermal conductivity of graphene and the formation of the complex graphene–water interface. Even though the curved graphene introduces an asymmetric assembly, no thermal rectification effect is observed for diverse directions of heat flux. It is demonstrated that the enhancement of overall thermal conductance of nanofluids is ascribed to the interface thermal transport rather than the base liquid with increasing temperature. This correlation is suppressed in a hydrophilic interface due to the structural change of liquid layer adjacent to the interface.

Effect of melting temperatures on the orientation and rheology of polyacrylate/silica (PAcr/SiO2) composite microspheres in twin‐screw extruder

“…In detail, the shear viscosity of composite melt dropped from 4.9 to 0.1 with continuous increase of the temperature in the range of 240°C–260°C, corresponding to the trend change of the color in Figure 4. It was attributed to the degree of molecular thermal motion and molecular entanglement 27,28 . On the other hand, it was clearly observed that the of composites melt decreased rapidly with the increase of shear rate at 300–2400 S −1 .…”

“…Especially, there existed tightly oriented structure at 250°C, which resulted in the powerful entanglement between macromolecules. However, as shown in Figure 3a, with the further increase of temperature, the orientation structure conducive to the entanglement of macromolecules was hard to construct because of the violent movement of macromolecular chains at 260°C 27,28 . On the other hand, the non‐Newtonian of the fluid was weakened at the relatively low temperature, leading to the more steady variation of and for the composite melt at 250°C.…”

“…On the other hand, the non‐Newtonian of the fluid was weakened at the relatively low temperature, leading to the more steady variation of and for the composite melt at 250°C. For investigation, it was liable to take shape the uniformly distributed orientation structure with long diameters, 28 which was ascribed to the compact chain and entanglement structure (Figure 2). Furthermore, the non‐linear variation on key values of for the composite fluids was observed with the increase of the temperature (Figure 5).…”

“…As mentioned in Figure 2, the results of orientation distribution could be explained by the fact that, with increasing the temperature, the orientation degree of the microfibers displayed an obvious non-linear change, leading to the remarkable capability discrepancy. 27,28 During the heating process, the thermal motion of the macromolecules of the composite microspheres was violent with disentanglement effect. Thus, it was tough to form interconnections and compact orientation microfiber.…”

Synthesis and characterization of Graphene Oxide and its reduction with different reducing agents

“…Graphene is the thinnest and strongest material having a two-dimensional (2D) structure with sp 2hybridized carbons [1][2][3]. The material based on graphene has been widely utilized in support of several advanced purposes namely Li-ion batteries, Supercapacitors, etc [4][5][6][7][8][9][10][11][12][13][14][15]. For the synthesis of GO, various synthesis methods in particular thermal reduction [16], chemical reduction [17], electrochemical reduction [18] have been used.…”