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Concentrated Solar Power (CSP) is one of the developing alternative energy technology, where mirror or lenses are used to concentrate sunlight from a large area and stored in collector filled with heat transfer fluid (HTF). The stored energy from HTF is then used to produce steam for power generation. Nanoparticle Enhanced Ionic Liquids (NEILs), inclusion of nanoparticles into Ionic Liquids (ILs), are considered as a potential HTF for CSP applications. In this present paper, we have experimentally investigated the density, rheological behavior, and thermal conductivity of NEILs forming with N-butyl-N,N,N-trimetylammonium bis(trifluormethylsulfonyl)imide ([N 4111 ][NTf 2 ]) IL and 1 wt% Al 2 O 3 nanoparticles (spherical and whiskers) and carbon black. The experimental results show that NEILs with whisker-shape nanoparticles show highest thermal conductivity enhancement, which is ∼7%. The rheological behavior of NEILs shows the shear thinning behavior occurs at all the measured temperatures and the shear thinning increases with temperature. The inclusion of nanoparticles into ILs enhances the viscosity compared to the base IL and it is highly dependent on the temperature, where viscosity sharply decreases with the increase of temperature. The possible mechanisms of this enhancement are discussed in the paper. [ABSTRACT FROM AUTHOR]

Abstract: Next generation solar thermal collector requires working fluid with high heat storage capacity as well as high temperature thermal stability to reduce its operating cost. Ionic liquids (ILs) are considered as a potential working fluid for next generation solar collector due to suitable thermophysical properties. However, Nanoparticle Enhanced Ionic Liquids (NEILs), a class of nanofluids, can further enhance the thermophysical properties of ILs. In this study, an experimental assessment on NEILs was performed by measuring thermophysical property and evaluating forced convection performance. Experimental results show clear advantages of the NEILs over the base ILs both in heat storage capacity and heat transfer performance. Up to 6% enhancement in thermal conductivity, 23% enhancement in heat capacity, and 20% enhancement in convective heat transfer performance has been observed for the 1% (Weight%) aluminium oxide (Al2O3) enhanced ILs compared to the base ILs. Our current study lays the foundation for future studies to explore further investigation to evaluate NEILs as a potential working fluid for the next generation solar collectors. [Copyright &y& Elsevier]

Nanoparticle Enhanced Ionic Liquids (NEILs) are the new heat transfer fluids for direct absorption solar collectors and are comprised of small vol/wt percentage of nanoparticles in base ionic liquids (ILs). In the present paper, NEILs are synthesized by dispersing Al 2 O 3 nanoparticles in 1-butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonylimide ([C 4 mim][NTf 2 ]) ILs. The radiative properties of NEILs are investigated with different sizes and shapes (one rod-shaped type sized 10 × 100nm and four spherical sizes of 10 nm, 30 nm, 60 nm, and 90 nm) of Al 2 O 3 nanoparticles. Five different concentrations (0.02%, 0.04%, 0.06%, 0.08%, and 0.1% wt) of NEILs were synthesized to investigate the concentration effect on radiative properties. The addition of Al 2 O 3 nanoparticles greatly increased the light absorption capabilities of the ionic liquid [C 4 mim][NTf 2 ], with at least a 26% decrease in transmittance observed with only 0.02% wt of nanoparticles. Differences in UV–vis absorption were more apparent in smaller concentrations; as much as 20% difference between nanoparticle types and larger concentrations varied in transmittance by as little as 5% between nanoparticle types. Nanofluids made of rod-shaped nanoparticles typically generated higher percentage transmittance values in 0.02%, 0.04%, and 0.06% wt of nanoparticles and were therefore less able to absorb light. Nanofluids made of 10 nm spherical nanoparticles yielded smaller percentage transmittance values at higher concentrations, as little as 2.7% transmission at 0.1% wt, and were therefore better able to absorb light. After completing the nanoparticle size and shape studies, three more NEILs were created from the ideal nanoparticle size and concentration in [C 2 mim][NTf 2 ], [C 6 mim][NTf 2 ], and [C 10 mim][NTf 2 ] ILs. This investigation revealed an increase in percentage transmittance with increasing carbon chain length. [C 2 mim][NTf 2 ] was determined to be the best-absorbing NEILs transmitting as little as 2.2% of light. Plausible reasons for the experimental results are discussed. • Addition of nanoparticles enhances the absorption ability of the base ionic liquids. • NEILs made of 10 nm nanoparticles yielded smaller percentage transmittance values at 0.1% wt concentration. • A shorter carbon chain length on the cation of the ionic liquids corresponded to a smaller percent transmittance. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 × 50 mm and 50 × 50 × 75 mm in heated from below. The NEILs were synthesized by dispersing different wt% (0.5, 1.0, and 2.5) of aluminum oxide (Al 2 O 3 ) nanoparticles of two different particle shapes (spherical and whiskers) into N-butyl-N-methylpyrrolidinium 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 explained by the change of thermophysical properties, which indicates that other factors may play significant roles in this phenomenon and the possible reasons of the degradation is discussed in this paper. [ABSTRACT FROM AUTHOR]

Experimental 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. [ABSTRACT FROM AUTHOR]

• Based on the particles size, no significant difference was observed in the density and viscosity of ILs based nanofluids. • Average ∼ 13.71% enhancement of viscosity was recorded for 1 wt% ILs based nanofluids. • Maximum average 9.73% enhancement of thermal conductivity of ILs based nanofluids was found for 10 nm nanoparticles. Concentrated Solar Power (CSP) systems rely on stable heat transfer fluids (HTFs) with favorable thermophysical properties to uphold high energy storage capacity and reduce costs. Ionic Liquids (ILs) is one of the potential HTFs for the next generation CSP systems. Nanoparticles are often mixed with the ILs to enhance the thermophysical properties of the base ILs. This paper presents the experimental assessment of the nanoparticle's size effect on density, viscosity, and thermal conductivity of Ionic liquids (ILs) based nanofluids. ILs based nanofluids was synthesized by dispersing 1 wt% aluminum oxide (Al 2 O 3) nanoparticles with difference particle sizes:10 nm, 30 nm, 60 nm, and 90 nm into 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([C 4 mim][NTf 2 ]) IL. The density, viscosity, and thermal conductivity were measured within the temperature ranges of 20–70 °C, 10–90 °C, and 10–70 °C, respectively. The enhanced density of ILs based nanofluids was noticed, compared to the base ILs, however, no significant density difference was observed based on nanoparticles size. Based on the size of the nanoparticles, no significant difference was observed in the viscosity of ILs based nanofluids and average ∼ 13.71% enhancement of viscosity was recorded for 1 wt% ILs based nanofluids. However, a maximum 9.73% enhancement in the effective thermal conductivity of ILs based nanofluids was found for 10 nm nanoparticles for 1 wt% ILs based nanofluids. Depending on the nanoparticle's concentration, maximum viscosity and thermal conductivity enhancement was reported 30% and 11% respectively for 2 wt% ILs based nanofluids with 10 nm nanoparticles. [ABSTRACT FROM AUTHOR]