Enhanced thermophysical properties of NEILs as heat transfer fluids for solar thermal applications

Abstract

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.

A review on molten-salt-based and ionic-liquid-based nanofluids for medium-to-high temperature heat transfer

“…Only Liu et al [33] tested data above 80°C, and they found that the k enhancement of the high concentration (0.06 mass%) increases with the increase in temperature, while for the low concentrations (0.01 mass% and 0.03 mass%) the enhancements are almost independent on temperature. The results by Chen et al [96] also showed that the enhancement at 0.01 mass% is steady, and the [90] and [94] with the permissions from Elsevier increase trend of SiC with 0.03 mass% is quite similar to the data of 0.03 mass% MWCNT by Wang et al [32]. By comparing between the experimental data from these three works, it reveals that the effective order is: GE [ MWCNT [ SiC.…”

“…Most experimental data indicate that l increases with the increase in NP concentration, but only Liu et al [33] found that the l is slightly decreased when adding the NPs. Paul et al [94] found that the Krieger-Dougherty model can also fit well with the experimental data of l, as shown in Fig. 3b.…”

“…Fox et al [95] realized that the enhancement ratio of k increases significantly with the increase in temperature, which is quite different from the results by Paul et al [94]. They found that the whisker-shaped NP (Al 2 O 3 ) is more beneficial than the sphere shape.…”

“…4. Nieto de Castro et al [93] and Paul et al [94] found that the enhancement ratio of k is nearly independent of the temperature, and it increases clearly with the increase in NP mass fraction. From Castro's work, it can be seen that the effective order to increase k for ILs is:…”

Thermal energy storage of molten salt –based nanofluid containing nano-encapsulated metal alloy phase change materials

“…The addition of nanoparticles to a base fluid implies an increment in the thermal conductivity of the nanofluid due to the higher thermal conductivity of the solid. Furthermore, although according to the mixture rule the specific heat of the nanofluid should decrease due to the lower specific heat of the nanoparticles, abnormal enhancements in the specific heat capacity of molten salts and ionic liquids have been reported [14][15][16][17][18][19][20][21][22][23][24][25][26]. This enhancement provides an increase in the sensible heat storage capacity of the TES material thus improving the efficiency of the storage system.…”