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The most important thermal and rheological properties of water-based CaCO3/SiO2 dual hybrid nanofluid (DHNF) at overall volumetric concentrations of the nanoparticles from 0.1 to 0.5 and different volume fractions at temperatures of 15–60 °C have been studied. Prepared DHNFs consisted using SDS and ultrasonic homogenizer. Stability analysis of the DHNFs performed by changing ultrasonication time and power. The optimum consistency conditions and volume fractions of the nanoparticles determined for the prepared DHNFs. Specific heat capacity, thermal conductivity and resistivity, usual viscosity and density of the DHNFs studied, experimentally, compared with preexisting models, and finally, theoretical models with 99% precisions suggested. Maximum augmentation in thermal conductivity attained to 21.8% for 80:20 corresponding volume ratio and 0.5 vol% total concentration. At these conditions, maximum reduction in heat capacity occurred as 1.08%, and the greatest reduction in thermal resistivity got about 22.2% at 60 °C. Usual viscosity and density increased as 36.9 and 1.2%, respectively. [ABSTRACT FROM AUTHOR]

The most currently used ionic liquids (ILs) are protic ionic liquids (PILs), subject to extensive investigation regarding their physical properties. These compounds along with their mixtures with other substances such as salts and solvents, serve as electrolytes in next generation electrochemical smart devices, and emerge as viable candidates to replace conventional Heat Transfer Fluids (HTFs) in various energy applications. Despite the extensive number of studies, important information about this kind of compounds is still unknown, such as the effect of alkyl chain length on thermal and thermophysical properties, as well as toxicity. This work, extending previous studies of our group, summarizes the liquid range, heat capacity and acute toxicity level of six ammonium ILs: specifically, n-alkyl-ammonium nitrate ILs with increasing alkyl chain length (n = 2, 3, 4, 5, 6, 8). For this study, the synthesis of the three ILs with the longest alkyl chain was performed, along with DSC, TGA and toxicity measurements. It was observed that an increase in alkyl chain length resulted in a decrease in short-term thermal stability and an increase in melting temperature, indicating a reduction in the liquid range. A compensation effect between enthalpy and entropy of melting was observed for the studied chain lengths. The isobaric specific and molar heat capacities increase with temperature for all the compounds studied here, and good correlations were obtained between molar heat capacity and the number of carbon atoms in the alkyl chain for every temperature. Finally, most of the ILs are non-toxic, although toxicity increases with alkyl chain length. [ABSTRACT FROM AUTHOR]