Thermophysical properties of base ionic liquids (ILs) and nanoparticle enhanced ionic liquids (NEILs) were measured experimentally. NEILs are formed by dispersing different wt% (0.5, 1.0, and 2.5) of Al 2 O 3 nanoparticles in four base ILs. NEILs show enhanced thermal conductivity, viscosity, and heat capacity compared to the base ILs. NEILs show shear thinning behavior at all the measured temperatures and the enhancement of viscosity was predicted by the aggregation model with high aggregation factor. Maximum thermal conductivity enhancement was observed by ~11% for 2.5 wt% NEILs. The experimental effective thermal conductivity could not predicted by the aggregation model with the same aggregation factor. However, the theoretical model considering interfacial layer of the particle/liquid interface (with interfacial layer thickness 2 nm and interfacial layer thermal conductivity,) could predict the effective thermal conductivity of NEILs. Heat capacity of NEILs shows much higher value compared to the base ILs and the theoretical model could not predict that enhancement. The strong interaction between the nanoparticles surface to ions of the ionic liquids was considered as the potential factor for those enhancements of thermophysical properties.

Experimental investigations were carried out regarding natural convection heat transfer of Nanoparticle Enhanced Ionic Liquids (NEILs) in rectangular enclosures of two different sizes with dimensions length×width×height, 50×50×50mm and 50×50×75mm in heated from below. The NEILs were synthesized by dispersing different wt% (0.5, 1.0, and 2.5) of alumina (Al 2 O 3) nanoparticles of two different particle shapes (spherical and whiskers) into N-butyl-Nmethylpyrrolidinium bis{(trifluoromethyl)sulfonyl} imide, ([C 4 mpyrr][NTf 2 ]) ionic liquid (IL). Heat transfer related thermophysical properties, i.e. density, viscosity, thermal conductivity, and heat capacity of base IL and NEILs were also measured and reported. The experimental measurement shows enhanced density, thermal conductivity, viscosity, and heat capacity of NEILs compared to the base IL and they increase with the nanoparticle concentration. However natural convection heat transfer coefficient was observed to deteriorate for the NEILs compared to the base IL irrespective of the shapes of the particles and aspect ratio of the enclosure and the deterioration increases with the increase of nanoparticle concentration. Interestingly spherical Al 2 O 3 NEILs was observed to affect more adversely compared to the whiskers Al 2 O 3 NEILs. The observed degradation of the heat transfer performance of the NEILs could not fully be explainedby the change ofthermophysical properties, which indicates that other factors may playsignificant roles in this phenomenon and the possible reasons of the degradation is discussed in this paper.

Nanoparticle Enhanced Ionic Liquids (NEILs) were synthesized by dispersing aluminum oxide (Al 2 O 3) nanoparticles in 1-butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide, ([C 4 mim][NTf 2 ]) ionic liquids (ILs). The experimental assessment of NEILs includes investigating the effective thermophysical properties and forced convection heat transfer under laminar and turbulent flow regime. The results show that thermal conductivity and heat capacity enhanced up to ~11% and ~49% respectively for 0.9 vol% NEILs. The rheological behavior of NEILs shows non-Newtonian shear thinning behavior with shear viscosity decreasing with increasing shear rate. The viscosity of NEILs shows much higher value compared to the base ILs for a small amount of nanoparticles dispersion and also has a strong temperature dependency. Measured viscosity and thermal conductivity were found to be much higher than predicted by the well-established model for dilute suspensions. The convective heat transfer performance increases with the nanoparticles concentration within the measured nanoparticles vol%; up to ~27% and ~40% enhancement in heat transfer coefficient was found in laminar and turbulent flow regime respectively. The possible mechanisms of the enhanced thermal performance are discussed.

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a b s t r a c tExperimental investigations were carried out to evaluate thermophysical properties, i.e. density, viscosity, heat capacity, and thermal conductivity and high temperature forced convection behavior of N-butyl-N,N,N-trimetylammoniumbis(trifluormethylsulfonyl)imide ([N 4111 ][NTf 2 ]) ionic liquid (IL) for its potential application in concentrated solar power (CSP). Results from the experiments will be useful in assessing the potential of using ILs for solar thermal collectors. Experimental results show that thethermal conductivity was slightly decrease with the increase of temperature; vary from 0.124 to 0.121 W/m K for a change in temperature of 283-343 K, strong temperature effect on the viscosity of IL was observed and maintain an exponential relationship with the temperature; heat capacity increases linearly with temperature measured from 298 to 618 K. Forced convection performance of the IL was studied in a circular tube under both in laminar and turbulent conditions. Although the heat transfer coefficient of the IL was found to be lower compared to the De-Ionized (DI) water, its thermal stability and other attractive properties may make it a viable candidate for solar collector use. Our experimental results also established that Shah's equation and Gnielinski's equation can predict forced convection performance of IL for both the laminar region and turbulent region respectively.

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This paper presents an experimental study of natural convection heat transfer for an Ionic Liquid. The experiments were performed for 1-butyl-2, 3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, ([C4mmim][NTf2]) at a Rayleigh number range of 1.13×107 to 7.7×107. In addition to determining the convective heat transfer coefficients, this study also included experimental determination of thermophysical properties of [C4mmim][NTf2] such as, density, viscosity, heat capacity, and thermal conductivity. The results show that the density of [C4mmim][NTf2] varies from 1.437–1.396 g/cm3 within the temperature range of 10–50°C, the thermal conductivity varies from 0.125–0.12 W/m.K between a temperature of 10 to 70°C, the heat capacity varies from 1.015 J/g.K–1.760 J/g.K within temperature range of 25–340°C and the viscosity varies from 243cP–18cP within temperature range 10–75°C. The results for density, thermal conductivity, heat capacity, and viscosity were in close agreement with the values in the literature. Measured dimensionless Nusselt number was observed to be higher for the ionic liquid than that of DI water. This is expected as Nusselt number is the ratio of heat transfer by convection to conduction and the ionic liquid has lower thermal conductivity (approximately 20% of DI water) than DI water.