# Fewer Dimensions for Higher Thermal Performance: A Review on 2D Nanofluids
## 2 Types of 2D Nanofluids
### Hybrid  
The use of hybrid nanofluids as nanocomposite fillers are a promising but not completely studied route. Indeed, hybrid nanofluids may utilize the synergistic overall effect of the combined usage of two or more types of nanomaterials and related nanostructures, and they are capable of surpassing the beneficial thermophysical features of the traditional mono suspended nanofluids. This results in the improved heat transfer and thermal storage capacities of hybrid nanofluids, which also enables the miniaturization of thermal management devices and systems. Examples include the hybrid formulations of graphene or graphene oxide nanofluids with a very wide spectrum of possible coupling arrangements with different nanomaterials from the hematite to the cotton seed green nanocomposite. Askari et al. [112] prepared hybrid nanofluids with Fe\({}_{3}\)O\({}_{4}\)/Gr nanoparticles dispersed in water and studied their TC. As a result, the researchers reported an increase of 32% in the TC at 40 \({}^{\circ}\)C for the nanofluid with a weight fraction of 1% wt. The investigation team also evaluated the heat transfer behavior of the nanofluids in a tube heat exchanger, reporting an increase of 14.5% in the HTC for the nanofluid with 0.1% wt. under a regime defined by a Reynolds number of 4248 compared to that of the water alone. The viscosity of the 0.5% wt. nanofluid was 1.15 mPa\(\cdot\)s at 20 \({}^{\circ}\)C, which is not significant when considering its potential applications. In the experimental work performed by Barai et al. [113], a rGO/Fe\({}_{3}\)O\({}_{4}\) nanocomposite was synthesized using ultrasonication. The nanocomposite had a nearly spherical morphology with 10 to 20 nm-sized Fe\({}_{3}\)O\({}_{4}\) nanoparticles finely dispersed on the rGO nanosheets. This fine dispersion was due to the collapse of the cavities provoked by the sonication process, which in turn led to the formation of shock waves, intense mixing, shearing action, and turbulence, which causes the total exfoliation of the rGO nanosheets. The synthesis procedure of the rGO-Fe\({}_{2}\)O\({}_{3}\) nanocomposite is schematically illustrated in Figure 11. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Reference** & **Authors/Year** & **Concentration** & **Base Fluid** & **Main Findings** & **Remarks** \\ \hline \multirow{3}{*}{[110]} & \multirow{3}{*}{Sundar et al., 2023} & MXene at from & & & & Approximate 18\% \\  & & 0.1\% wt. to & & & Liquid Mixture & 56.6\% increase in the \\  & & 1.0\% wt. & & & the TC at 1.0\% wt. & viscosity at \\ \hline \multirow{3}{*}{[111]} & \multirow{3}{*}{Qu et al., 2023} & \multirow{3}{*}{MXene at from 10 to 300 p.p.m.} & & & & \\  & & & & & the photothermal & \\ \cline{1-1}  & & & & conversion & & \\ \cline{1-1}  & & & & efficiency at & 220 p.p.m. & 220 p.p.m. \\ \hline \end{tabular}
\end{table} 
Table 5: _Cont._The authors prepared nanofluids with diverse volume fractions between 0.01% vol. and 0.2% vol. of the referred composite nanoparticles suspended in water and studied the TC and viscosity of the nanofluids at temperature values ranging from 25 \({}^{\circ}\)C to 40 \({}^{\circ}\)C. In addition, a study of convective heat transfer was also performed considering the 0.01% vol. and 0.02% vol. of the rGO-Fe\({}_{3}\)O\({}_{4}\) nanofluid and a pressure-drop analysis comparing the water and the 0.01% vol. nanofluid. The authors found that the developed nanofluids exhibited a significant enhancement in the TC of 83.4% for the 0.2% vol. nanofluid at 40 \({}^{\circ}\)C. It was also confirmed that for a given volume fraction of the nanoparticles in the base fluid, the TC increased with the rising temperature values. This evidence was interpreted based on the intensification of the Brownian motion associated with the nanoparticles with increasing temperature, resulting in greater heat dissipation induced by the nanoparticles.