Recent reports that a host liquid's thermal properties can be augmented by dispersal of small quantities of nanoparticles have stimulated intense interest as an intriguing avenue to produce advanced heat transfer fluids. But effects are challenging to exploit in practical settings because it is difficult to prepare refrigerant-based dispersions displaying sufficient long-term stability. Moreover, the most dramatic enhancements in thermal conductivity obtained using anisotropic nanomaterials (e.g., carbon nanotubes) are achieved at the expense of a severe viscosity increase. Here we overcome these limitations by introducing a robust surfactant-mediated dispersal method that enables stable suspensions containing a range of nanomaterials to be straightforwardly prepared as additives to ordinary commercial refrigerants. We apply this approach to formulate a new class of nanorefrigerants containing graphene nanosheets that uniquely match the superior thermal conductivity enhancements attained in carbon nanotube suspensions without their accompanying viscosity penalty. These suspensions can be directly substituted for conventional refrigerants to inexpensively achieve increased efficiency in many thermal management applications.
