Experimental measurements and molecular dynamics simulations are used to determine the density, heat capacity, self-diffusivity, shear viscosity, and thermal conductivity of six ionic liquids over a range of temperatures. The ionic liquids examined are 1-butyl-3-methylimidazolium bis[(perfluoroethyl). The results of this work suggest that several of these ionic liquids have properties that would enable them to be successful high temperature heat transfer fluids. In particular, their energy storage densities and thermal conductivities are quite favorable when compared to conventional heat transfer fluids. The low temperature viscosities of the ILs are significantly higher than conventional fluids, but the viscosities drop rapidly with increasing temperature. The simulations, which are purely predictive, agree quantitatively with the experimental data for density and qualitatively for other properties. It is shown that the simulated thermal conductivity can be adequately correlated with density and molecular weight of the [Tf 2 N]-based ionic liquids.
Solvent extraction of cesium ions from aqueous solution to hydrophobic ionic liquids without the introduction of an organophilic anion in the aqueous phase was demonstrated using calix[4]arene-bis(tert-octylbenzo-crown-6) (BOBCalixC6) as an extractant. The selectivity of this extraction process toward cesium ions and the use of a sacrificial cation exchanger (NaBPh(4)) to control loss of imidazolium cation to the aqueous solutions by ion exchange have been investigated.
803-507-8560 RECEIVED DATEKEYWORDS. Nanoparticle enhanced ionic liquid, heat transfer fluid, concentrating solar power, 1-Butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, nanofluid INTRODUCTIONInterest in capturing the energy of the sun is rising as demands for renewable energy sources increase. One area of developing research is the use of concentrating solar power (CSP), where the solar energy is concentrated by using mirrors to direct the sunlight towards a collector filled with a heat transfer fluid (HTF). 1 The HTF transfers the collected energy into pressurized steam, which is used to generate energy. The greater the energy collected by the HTF, the more efficent the electrical energy production is, thus the overall efficiency is controlled by the thermal fluid. Commercial HTFs such as Therminol ® (VP-1), which is a blend of biphenyl and diphenyl oxide, 2 have a significant vapor pressure, especially at elevated temperatures. 1 In order for these volatile compounds to be used in CSP systems, the system either has to be engineered to prevent the phase change (i.e., volatilization and condensation) through pressurization of the system, or operate across the phase change. 3 Over thirty years ago, a class of low-melting organic compounds were developed with negligible vapor pressure. 4 These compounds are referred to as ionic liquids (ILs), which are organic-based compounds with discrete charges that cause a significant decrease in their vapor pressure. 5 As a class, ILs are molten salts with a melting point below 100 o C and can have a liquidus range approaching 400 o C, and in several cases freezing points being below 0 o C. 6 Due to the lack of an appreciable vapor 1 pressure, volatilization of an IL is not possible at atmospheric pressure, 5 which would lead to a simplification of the design if used as a thermal fluid and for energy storage materials. 7 Though the lack of a vapor pressure does not make the use of ILs a better HTF, the lack of a vapor pressure is a compliment to their higher heat capacity, higher volummetric density, and thus higher volumetric heat capacity. 8 These favorable physical properties give ILs a pontential advantage over the current commerically used thermal fluids. Also within the past decade nanofluids have gained attention for thermal conductivity enhancment of fluids 9 , but little analysis has been completed on the heat capacity effects of the nanoparticle addition.The idea of ILs or nanofluids as a HTF is not new, as there are several references that have proposed the idea. 8, 10 However, the use of ionic liquid nanofluids containing nanomaterials other than carbon nanotubes has never before been studied. Here, for the first time, nano-particle enhanced ILs (NEILs) have been shown to increase the heat capacity of the IL with no adverse side effects to the ILs' thermal stability and, only at high nanoparticle loading, are the IL physical properties affected. An increase of volumetric heat capacity translates into a better heat transfer fluid as more energy i...
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