Nowadays, different types of strategies are proposed and tested to find the best scenario for upgrading the productivity of heat transfer fluids, especially nanofluids. Some optimum empirical conditions demonstrated that the best size, shape, and nature of nanoparticles and their dispersion have positive influences on nanofluid thermal conductivity improvements. Therefore, the specific physicochemical properties of the base fluid can be taken into account as one of the decisive factors in heat transfer operations. Deep eutectic solvents (DESs) are nominated as valuable materials to meet the demands for sustainable ecological processes and open opportunities for overcoming the limitations of conventional fluids. The purpose of this study is to briefly introduce the DESs for evaluating their thermal potential applicability and their use to produce nanofluids. DES-based nanofluids represent a new and creative type of heat transfer fluids that possess high potential in different target applications and are not harmful to the environment. This type of nanofluid has higher thermal properties than the base DESs. Increasing the temperature and the volume fraction of nanoparticles lead to further increment in their thermal properties. In this study, the chemical structure and preparation method have been addressed for the DES and DES-based nanofluids. Also, the theoretical approaches have been considered for modeling and predicting their behavior. A discussion was extended to investigate the usage of DES as host fluid for producing nanofluids, and its advantages and drawbacks are also presented. It is deduced that the DES-based nanofluids are one of the smart choices for the progression of nanofluids and give the most promising results for application in heat transport fluids. The contents may shed light on a detailed awareness of the heat transfer potential of the DESs.
