# Fewer Dimensions for Higher Thermal Performance: A Review on 2D Nanofluids
## 6 Limitations and Future Prospects  
The fundamental limitations and future prospects related to 2D nanofluids are summarized in the following points:* The measurement of the thermophysical properties of 2D nanofluids should be further improved. For instance, the actual TC data may be erroneous since incoming data from identical thickness samples differ appreciably from each other, which is not surprising given the lateral sides and the operating conditions considerably, hindering an accurate measurement and the comparison of results. * The results on the TC of 2D nanofluids show that the maximum TC enhancement did not correspond to the maximum zeta potential. Hence, a precise concentration level optimization is the main factor for achieving the optimal heat transfer nanofluid. * Regarding the tungsten disulfide nanofluids with the addition of surfactants (e.g., SDS), the enhanced amount of SDS reduced the TC of 2D nanofluids. However, under high temperature values the behavior oscillates. The reason behind this fact could be the detachment of the molecules of the surfactant and the consequent interaction between the WS\({}_{2}\) nanosheets. Thus, further studies are required to better understand this high-temperature behavior. * Further experimental evaluation studies of 2D nanofluids are recommended to stablish a database with the stability over time, specific heat, TC, and rheological characteristics for comparison purposes. * More experimental and numerical works on the size reduction possibility when using 2D nanofluids in heat transfer equipment and in systems such as PV/T are required such as those analyzed in the work conducted by Sreekumar et al. [142]. * Despite the extremely high intrinsic TC of Gr, the verified increases in the TC of Gr nanofluids were up only by 50%. This fact should be further investigated with the aid of numerical modeling and in-depth theoretical studies to achieve a better TC. * Since it was already reported that the viscosity of the Gr nanofluids is higher than that of other metals and metallic oxide nanofluids that may result in enhanced flow friction and pumping power needs, an accurate investigation of the friction, pressure drop, and pumping power needs is recommended to fully interpret the tradeoff between the improved TC and the augmented friction and pumping requirements. * The economic feasibility of Gr nanofluids should be further evaluated to identify the balanced commitment between the technical and economic feasibility of Gr nanofluid solutions. Most of the economic challenges are associated with current Gr synthesis procedures, which are expensive, material intensive, and energy demanding. Consequently, welcome advancements in Gr manufacturing would relieve the technical and economic limitations for the practical application of Gr nanofluids. * Further hybrid evaluation methods should be implemented through the combined usage of molecular dynamic numerical simulations and fluid dynamic laboratory experiments to achieve a better understanding the behavior of 2D nanofluids. * Studies on the impact of the hybrid approach of the inclusion of metal (e.g., copper, gold) or metal oxides (e.g., iron oxide) into Gr nanosheets should be undertaken in order to improve the thermal characteristics of Gr nanofluids. * More research on the stability, TC, and viscosity of WS\({}_{2}\) nanoparticles suspended in ethylene glycol nanofluids with the addition of surfactants should be conducted. Playing the role of stabilizers and rheological modifiers, the careful use of surfactants such as SDBS and CTAB can improve suspension stability over time and reduce the viscosity of 2D nanofluids. * Further studies are recommended to evaluate as accurately as possible the real electronic contribution of phonon transport to the TC of Gr. Definitive laboratory data supporting the electronic contribution are still missing. * Further experiments should be conducted on the interfacial thermal conductance of 2D nanofluids and nanomaterials.