# Fewer Dimensions for Higher Thermal Performance: A Review on 2D Nanofluids
## 2 Types of 2D Nanofluids
### Graphene/Graphene Oxide
[61] employed GO/water nanofluids to conduct flow boiling experiments in microchannels. The heat transfer capability was reduced as the concentration increased. The authors argued that the deposition process of GO nanoparticles was intensified with the increasing flow rate, operating temperature, and concentration of the nanoparticles. Table 2 summarizes some recent experimental works on 2D Gr family nanofluids. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Reference** & **Authors/Year** & **Concentration** & **Base Fluid** & **Main Findings** & **Remarks** \\ \hline
[62] & \begin{tabular}{c} **Ahammed et al., 2016** \\ \end{tabular} & \begin{tabular}{c} Gr at 0.05\%, 0.10\%, \\ and 0.15\% vol. \\ \end{tabular} & \begin{tabular}{c} Water \\ and 0.15\% vol. \\ \end{tabular} & \
\begin{tabular}{c} Viscosity increased \\ by approximately \\ 47\% at 0.15\% vol. \\ \end{tabular} &
\begin{tabular}{c} Surface tension \\ decrease of \\ approximately 19\% \\ at 0.15\% vol. \\ \end{tabular} \\ \hline
[16] & \begin{tabular}{c} Das et al., 2019 \\ \end{tabular} & Gr at 0.1\% wt. & Water & \
\begin{tabular}{c} 17\% increase in \\ the TC. \\ \end{tabular} &
\begin{tabular}{c} Considerable \\ increase in the \\ viscosity. \\ \end{tabular} \\ \hline
[63] & \begin{tabular}{c} Dong et al., 2021 \\ \end{tabular} & Gr at 0.2\% wt. & \begin{tabular}{c} Propylene \\ glycol–water \\ Mixture \\ \end{tabular} & \begin{tabular}{c} The TC increased \\ with increasing \\ concentrations \\ until 0.2\% wt. \\ \end{tabular} & \
\begin{tabular}{c} The ITC increased \\ with increasing \\ concentrations \\ until 0.2\% wt. \\ \end{tabular} &
\begin{tabular}{c} The ITC increased from \\ from \\ approximately 6\% \\ to 23\%, depending \\ on the added \\ surfactant. \\ \end{tabular} \\ \hline
[65] & \begin{tabular}{c} Kanti et al., 2022 \\ \end{tabular} & \begin{tabular}{c} GO from 0.05\% to \\ 1.0\% vol. \\ \end{tabular} & \
\begin{tabular}{c} Water \\ the TC at 1.0\% vol. \\ \end{tabular} &
\begin{tabular}{c} 14.4\% increase in \\ time with the PVP \\ surfactant. \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Recent works on Gr, GO, and hybrid 2D nanofluids. Further studies on the decrease in the elevated cost of Gr nanomaterials and their derivatives and corresponding nanofluids are highly recommended since the current processing methodologies are very complex and demand the intensive use of chemicals and are otherwise energy consuming. A profound benefit-cost analysis should be performed to evaluate the use of Gr family nanofluids considering the balance between the obtained improvements in the thermophysical properties versus the high initial investment associated with such heat transfer solutions. More experimental works on the high temperature stability of Gr and GO nanofluids are required. In addition, there is a lack of studies on Gr and GO hybrid nanofluids in certain types of nanomaterials, such as metallic and metallic oxides. Innovative techniques based on the surface modification of Gr nanomaterials with hydrophilic groups should be further developed to ameliorate the stability over time of the Gr nanofluids. Additionally, further experimental investigation should be carried out to evaluate conclusively the trade-off between the extremely high values of TC inherent to Gr and derivative nanofluids and the increased density and viscosity leading to higher pressure drops, which are typical in this type of fluid. In this regard, there is a need to pursue the optimal concentration of Gr nanostructures that maximizes the TC of the thermal fluids and, simultaneously, minimizes the density and viscosity enhancements which, considering the published background on the subject, represents a significant challenge. Finally, more life cycle assessments of Gr nanomaterials are required to mitigate the negative impacts on the environment and human health derived from the production, use, and disposal of such materials.