# Fewer Dimensions for Higher Thermal Performance: A Review on 2D Nanofluids
## 7 Conclusions  
The fundamental conclusions of this review can be summarized in the following points:  
* The employment of 2D nanofluids can improve the thermal performance of heat transfer systems and devices. Hence, the dimensions of heat changers, heat pipes, and thermosyphons, among others, can be noticeably reduced, resulting in greater efficiency, reliability, reproducibility, and less associated EI. * The results of the TC measurement of 2D nanofluids with the addition of nanosheets revealed that the maximum TC enhancement did not coincide with the zeta potential maximum. Consequently, an accurate concentration of the nanoparticles is one of the most important factors for achieving the optimal heat transfer performance when employing 2D nanofluids. * The size reduction in heat transfer and storage equipment and systems using 2D nanofluids is an issue of relevance and has been studied previously. For instance, in the study performed by Sreekumar et al. [142] it was demonstrated that, from the same thermal output of a PV/T system, the MXene 2D nanofluids achieved a reduction in the solar collector area between 4.5 and 14.5%, depending on the concentration of the MXene in reference to a water-based operating PV/T system. * The rheological analysis suggested the formation of a structured network in the nanofluids of the WS\({}_{2}\) nanoparticles and showed that there was a transition from the viscous behavior to the elastic behavior in WS2 nanofluids with the addition of surfactants. This transition usually requires a higher initial pumping power in the system. * Gr nanofluids revealed a higher TC at much lower concentrations in comparison to those of the metallic and metallic oxides, such as silver, copper, alumina, and silica, exhibiting enhancements between 40% and 50% at only 0.1% wt. weight fraction. However, Gr nanofluids possess a higher density and viscosity, with the latter reported to be higher than that of the other mentioned nanofluids even at lower concentrations. * The improved thermophysical characteristics of the rGO are related to its monolayer or multi-layered nanostructures. Nonetheless, the adjacent rGO nanosheets cause them to aggregate into macro-scaled carbon allotropism. Consequently, the assurance of a homogeneous dispersion of the nanosheets is pivotal for the synthesis of rGO 2D nanofluids. * Two-dimensional nanofluids with the incorporation of Gr nanosheets are commonly found to exhibit higher convective heat transfer parameters than GO nanosheets. The difference may be related to the diverse order of the molecules in the base fluid in the proximity of the Gr nanosheets, parallel structure, and \(\pi\)-\(\pi\) plan stacking. * It is important to prevent the agglomeration and sedimentation of 2D nanoparticles in base fluids by modifying the charge distribution of their surface. The scientific community have used different technological solutions to tackle this limitation, including covalent functionalization by the modification of the chemical structure, non-covalent functionalization with the incorporation of surfactants, and plasma functionalization. Plasma functionalization usually involves very complex processes and overall costs. * The possibility of studying the thermal characteristics and mechanisms rarely detected in the bulk nanomaterials is one of the most remarkable characteristics of 2D nanomaterials and corresponding nanofluids. One example is the electronic contribution of the TC of the ballistic and hydrodynamic phonon transport in Gr. This contribution is as high as 10% and is important in thermoelectric applications. * Regarding 2D hybrid nanoparticles, the thermal contact resistance between the different components may limit the heat transfer capability in thermal management applications. This is the case in CNT/Gr nanofluids, where the thermal contact resistance between the individual Gr nanoflakes and the CNTs remains a problem that should be solved.