**8. Discussion and Future Directions**

This review article has covered carbon-based nanofluids, from the fabrication stages of the raw nanoparticles materials (i.e., ND, graphene, and CNT) and up to their employment in some of the commonly known thermal applications in the energy industry. In addition, it was shown how dispersions made of carbon allotropes possess the most favorable thermal properties and, when well handled, physical properties compared to any other type of nanofluids or conventional fluids. This is because these carbon-based materials, when dispersed in a base fluid attain unique features such as high thermal conductivity and specific heat capacity, high heat transfer rate, and lower pressure drop in the working system compared to other types of dispersed nanomaterials. Furthermore, the aforementioned suspensions cause the least corrosion and erosion effects on the hosting device [483], all of which are crucial parameters for the operation cycle. Moreover, the influence of the stability of these suspensions on their thermophysical properties was also highlighted along with the development in these properties prediction correlations. Nevertheless, there

are still some challenges and gaps in the scientific knowledge that need to be tackled for further advancement in the field and the possible industrial viability of such advanced fluids. Some of these issues are pointed out in this section.
