A review of the thermophysical properties and potential of ionic liquids for thermal applications

In recent years ionic liquids have received tremendous attention from researchers and industries mainly due to their unique properties, such as low vapor pressure, low toxicity, high thermal stability and recyclability. These liquids are also recognized as sustainable liquids with great potential for a wide range of applications. This article presents a critical review of the main thermophysical properties such as viscosity, density, specific heat capacity, thermal conductivity, thermal stability, and melting point of ionic liquids for their potential application as heat transfer fluids. Although there are a number of studies available in the literature in this regard, far fewer are the studies that consider thermal conductivity, and to the best of our knowledge, this is the first review that compiles an extensive number of studies and presents the main properties under the same conditions for a better comparison between the various ionic liquids available. From an engineering point of view, this article provides a critical and systematic overview of the different types of ionic liquids, and the influences of their structure and composition on the main properties that significantly impact their performances and applications. This review reveals that the structural composition and characteristics of ionic liquids make them excellent alternatives as heat transfer fluids and the knowledge of the tendency of their main properties under different conditions can facilitate not only their task-specific selection but also exploring their numerous potential applications particularly in thermal energy systems. This article is expected to provide knowledge to overcome the limitations of ionic liquid industrial applications in the very near future.