Ionic Liquids-Based Nanocolloids—A Review of Progress and Prospects in Convective Heat Transfer Applications

Abstract

Ionic liquids are a new and challenging class of fluids with great and tunable properties, having the capability of an extensive area of real-life applications, from chemistry, biology, medicine to heat transfer. These fluids are often considered as green solvents. Several properties of these fluids can be enhanced by adding nanoparticles following the idea of nanofluids. These ionic liquids-based nanocolloids are also termed in the literature as ionanofluids or nanoparticles-enhanced ionic liquids. This review summarizes the findings in both areas of ionic liquids and ionic liquids nanocolloids (i.e., ionic liquids with nanoparticles in suspension) with direct applicability in convective heat transfer applications. The review presents in a unified manner the progress and prospects of ionic liquids and their nanocolloids from preparation, thermophysical properties and equally experimental and numerical works. As the heat transfer enhancement requires innovative fluids, this new class of ionic liquids-based nanocolloids is certainly a viable option, despite the noticed drawbacks. Nevertheless, experimental studies are very limited, and thus, extensive experiments are needed to elucidate ionic liquids interaction with nanoparticles, as well as their behavior in convective heat transfer.

Appearance of a Solitary Wave Particle Concentration in Nanofluids under a Light Field

“…Without detailed knowledge of the optical properties of nanofluids, it is impossible to create next-generation solar collectors [ 11 , 12 , 13 , 14 , 15 ]. For example, [ 16 ] summarized the results of studies on the nanocolloids of ionic liquids (i.e., ionic liquids with nanoparticles in suspension), which can be directly applied to convective heat transfer. In [ 17 ], machine learning was used to develop Gaussian process regression models to describe the statistical correlations between the thermal conductivity and physical parameters of two-phase nanofluid components.…”

Thermophysical Properties of NH3/IL+ Carbon Nanomaterial Solutions

“…The experimental results related to the thermal conductivity of ionic liquids revealed the increase in thermal conductivity achieved by adding nanoparticles into the ionic liquid and the minor influence of temperature on several ionic liquids containing nanoparticles. The main arguments for these trends are thermal boundary resistance, layering phenomena, and clustering [33]. The thermal conductivity values are correlated by means of a linear equation as a function of temperature:…”

Design of concentrated colloidal dispersions of iron oxide nanoparticles in ionic liquids: Structure and thermal stability from 25 to 200 °C

“…The present study hypothesized that stable colloidal dispersions of nanoparticles (NPs) in ionic liquids (ILs) can be obtained by carefully adapting the NPs' interfacial properties with pure IL or adsorbed species and that they can be stable up to high temperatures, as high as 200 ˝C (473 K). Although such systems at high temperature are envisaged for heat transfer fluids [13] or lubricants [33], the charge of the NPs is seldom considered and never varied. Moreover, the nanostructure of the dispersion at high temperature has only been considered recently by DLS in molten salts [35].…”

“…The addition of charged nanoparticles to electrolytes of electrochemical devices can, for instance, improve the thermoelectric properties compared with the solvent alone [10] or improve electrochemical performance compared with the pure IL [11]. Such dispersions of NPs can also be considered as potential heat transfer fluids thanks to their improved thermal properties [12,13]. Other applications as the determination of ILs viscosities can be envisaged [14].…”

“…it decreases for mica surfaces in EMIM TFSI between 20 and 50 ˝C [31] whereas it increases or even appears for silica/mica surfaces in ethylammonium nitrate (EAN) between room temperature and 120 ˝C [32]. The use of ionic liquids at elevated temperatures is however extremely interesting for applications for example in the fields of heat transfer fluids [13], lubricants [33] or supercapacitors [11]. To be suitable, the ionic liquid-based systems need to be long-term stable at high temperature.…”