# Fewer Dimensions for Higher Thermal Performance: A Review on 2D Nanofluids
## 2 Types of 2D Nanofluids
### Titanium Carbide MXene
Considering they were working under a salinity gradient, performant directional ion transport was employed to obtain an enhanced osmotic energy conversion output exhibiting appreciable results, such as the output power density increase of 1.68 mW\(\cdot\)m\({}^{-2}\), which is a pathway towards better harvesting of the salinity gradient energy and towards promote the physical stimuli-facilitated, ion-related mass transport and energy conversion. Moreover, the stability over time, the TC, and electrical conductivity of MXene nanofluid would enable its wide application in advanced heat transfer systems. In the experimental work conducted by Rubbi et al. [103], a 2D nanofluid composed of MXene nanoparticles at weight fractions from 0.025 to 0.125% was developed, using soybean oil as the base fluid. The main steps of the preparation method used are presented in the schematic diagram of Figure 10.  
Considering the potential application of the developed nanofluid in a hybrid PV/T solar collector system, the investigation team reported that the nanofluid was thermally stable up to 320 \({}^{\circ}\)C and it possessed a TC value of 0.125% wt. that was 60.8% higher than that of the soybean oil base fluid. The maximum augmentation of the specific heat of the nanofluids was reported to be 24.5% at a 0.125 weight fraction. Furthermore, the density and viscosity of the nanofluid both changed with the inclusion of nanoparticles by 1% and 13.3%, respectively. Nevertheless, these properties decreased significantly at high temperatures and exhibited Newtonian behavior up to 100 s\({}^{-1}\) shear rates. Furthermore, the implementation of the prepared nanofluid on a PV/T system was tested using a numerical approach using COMSOL Multiphysics v. 5.5 software. The obtained results demonstrated that the use of the developed nanofluid resulted in a considerably improved performance  
Figure 10: Main steps of the preparation of the MXene/soybean oil 2D nanofluid. Adapted from [103]. compared with the operating fluids of water, alumina/water, and MXene/palm oil. One of the optimized outcomes was that the overall thermal efficiency achieved 84.3% using the developed nanofluid with a 0.07 Kg.s\({}^{-1}\) mass flow rate. Furthermore, the electrical output of the PV/T system was increased by 15.4% compared with the alumina in water nanofluids under an irradiance of 1000 W.m\({}^{-2}\) and a mass flow rate of 0.07 kg/s. The HTC was enhanced with rising mass flow rate and the maximum enhancement of 14.3% was found at 0.06 kg.s\({}^{-1}\) for the nanofluid compared with that of the alumina/water nanofluid. Additionally, Aslfattahi et al. [104] manufactured a nanofluid composed of MXene nanoparticles dispersed in silicone oil to be used in a concentrated solar photovoltaic thermal (CSPT) collector. The researchers found a considerable maximum TC enhancement of 64% at a 0.1% weight fraction of nanoparticles compared to that of the silicone oil itself. The authors also stated that the viscosity of the nanofluids was independent of the incorporation of MXene into the silicone oil and decreased with increasing temperature. Indeed, the viscosity was reduced by 37% in the case where the temperature was increased from 25 \({}^{\circ}\)C to 50 \({}^{\circ}\)C at different weight fractions of MXene, which was a promising result since the viscosity decrease will reduce the required pumping power in the system. Moreover, the research team also found that the synthesized nanofluid at a 0.1% weight concentration had thermal stability up to 380 \({}^{\circ}\)C. The most improved electrical efficiency of the CSPT collector was obtained when using the nanofluid with 0.1% wt. Adding more MXene nanoparticles into the silicone base oil will enhance the electrical efficiency of the PV cells because of the improved cooling of MXene nanofluids. Higher solar concentration resulted in a PV module with a higher average temperature, which in turn will raise the thermal energy gain. Table 5 presents some recently published works on 2D MXene nanofluids and hybrid forms.