Thermal Conductivity and Viscosity of Ionanocolloids for Applications in Thermal Energy Systems

Abstract

The efficiencies of the heat transfer processes and systems are directly conditioned by the applied heat transfer fluid. Despite the great technological advances in energy-related areas, the performance of the conventional fluids is way below the required by demand and thus innovative and more efficient fluids must be developed. In this sense, the use of ionic liquids as base fluids combined with nanoparticles having excellent thermal conductivities emerge as attractive alternatives to replace the commonly used heat transfer fluids such as water or ethylene glycol. These new ionic liquid-based nanofluids, termed here as "ionanocolloids" have recently gained increasing attention and lot of research have been performed studying their thermophysical properties for applications in diverse energy fields. Ionanocolloids have the remarkable chemical and physical features of the ionic liquids, such as negligible vapor pressure, high ionic conductivity and thermal stability, that make them more sustainable, eco-friendly and of safer operation. Additionally, given the large variety of cations and the organic and inorganic anions available, there are infinite types of ionic liquids and they can be tailored to have specific desired characteristics. In this work, an overview of the state of art concerning the thermal conductivity and viscosity of ionanocolloids has been done comparing the available literature results and providing a critical analysis of the impact of different operational conditions on each of these important properties. This systematic evaluation gives extreme valuable insights about the behaviour of different ionanocolloids under different conditions and it is essential for the consideration of the ionanocolloids for real-world applications, particularly in thermal energy systems.