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The present study analyzes on the reviews carried out by the previous researchers on the entropy generation caused by the flow and heat transfer of several composite nanofluids subject to varieties of geometries under the influence of several constraints of motions. The composite nanofluids include binary hybrid nanofluids and ternary hybrid nanofluids involving disparate base fluids with different suitable nanoparticles. The geometries considered are deformed surfaces (stretched/shrunk sheets, cylinders, and disks), channels and cavities. Several numerical techniques such as Runge-Kutta method and finite element/difference/volume methods are implemented in the investigations. The major and significant outcome of the review analysis is the entropy comparison for different types of nanofluids. Growth of the volume percentage of nanoparticles at a fixed mass flow rate enhances entropy formation. When porosity strength increases, the irreversible entropy production caused by fluid friction results in increased thermal efficiency of certain systems than magnetic entropies. Compared to single nanofluids, hybrid nanofluids display the maximum entropy. With increasing Rayleigh numbers, the frictional and magnetic entropies in composite nanofluids ameliorate significantly than thermal entropy.

To improve the efficiency of coal seam water injection, the influence of nanofluids on coal surface wettability was studied based on the nano drag reduction and injection enhancement technology in the field of tertiary oil recovery. The composition optimization and performance evaluation of nanofluids with nano-silica and sodium lauryl sulfate as the main components were carried out, and the effects of the nanofluid with the optimal ratio on coal wettability were studied through spontaneous upward imbibition experiments. The results show that the composite nanofluid has a lower surface tension, and the lowest value of the interfacial tension is 15.79 mN/m. Therefore, the composite nanofluid can enhance the wettability of coal. However, its effects on coal samples with different metamorphic degrees is different, that is, low rank coal is the largest, middle rank coal is the second, and high rank coal is the least. In addition, a functional relationship between time and imbibition height is found for pulverized coal with different particle sizes. When the particle size of pulverized coal is 60–80 mesh, the wettability of nanofluid to coal is best. The findings in this paper provide a new perspective for improving the water injection efficiency for coal seams with low permeability.

A two-phase lattice Boltzmann method (LBM) is used to study the natural convection heat exchange characteristics of Al2O3–H2O nanofluids and (Al2O3/Cu)–H2O composite nanofluids in a rectangular cavity in this paper. It can be found that the two-phase LBM is suitable for the study on natural convection heat exchange characteristics of nanofluids, and its correctness is verified. Firstly, the effects of temperature differences (∆T = 1 K and ∆T = 11 K), nanofluids volume fractions (φ = 0.01, 0.03 and 0.05) and kinds of fluid (water, Al2O3–H2O nanofluids and Al2O3/Cu–H2O nanofluids) on the free convection are researched. Then, temperature and streamline distributions of Al2O3/Cu–H2O nanofluids are investigated, respectively. Lastly, local Nusselt number and average Nusselt number distributions of different nanofluids along with Y direction are investigated. It can be found that Al2O3/Cu–H2O nanofluids show a larger enhancement than Al2O3–H2O nanofluids and water. Al2O3/Cu–H2O and Al2O3–H2O nanofluids can strengthen the heat transfer performance by 9.9% and 5% at the extreme compared with deionized water, respectively. Besides, the maximum enhancement ratio of Al2O3/Cu–H2O and Al2O3–H2O nanofluids is 9.8% and 4.5% at small temperature difference (ΔT = 1 K), respectively, which is greater than that (1.6% and 0.36%) at big temperature difference (ΔT = 11 K). [ABSTRACT FROM AUTHOR]

The working fluids with higher solar thermal conversion performance within broadband spectrum ranges are of great concern for direct absorption solar collectors (DASCs). Both metal nanoparticles with localized surface plasmon resonance (LSPR) effects and carbon nanomaterials have unique spectral absorption behaviors and have shown better photothermal performance in DASCs. In this paper, we attempted to prepare composite nanofluids including plasmonic bimetallic alloy and carbon nanomaterials to realize enhanced solar absorption and photothermal conversion performance. By taking ZIF-8-derived nitrogen-doped graphitic polyhedrons (ZNGs) as carrier, plasmonic bimetallic Ag-Au alloy nanoparticles were loaded on them by an impregnation-reduction method successfully. Ag-Au/ZNGs ethylene glycol nanofluids showed significant broadband absorption in the visible and near-infrared spectrum range at a lower concentration. Comparing to ethylene glycol, the photothermal conversion effeiency of all ZNGs nanofluids increased remarkablely. Plasmonic bimetallic Ag-Au alloy nanoparticles further improved the photothermal conversion efficiency, which was up to 74.35% for Ag-Au ZNGs nanofluids compared with 72.41%, 70.35% for Au/ZNGs, Ag/ZNGs respectively. This work presents a new way to enhance solar energy absorption and improve solar thermal conversion efficiency of nanofluids for DASCs. • Dual plasmonic Ag-Au/nitrogen-doped graphitic polyhedrons (ZNGs) nanofluids were designed in solar thermal application. • Ag-Au/ZNGs nanofluids show significant broadband absorption in the visible and near-infrared spectrum. • Photo-thermal conversion efficiency of the Ag-Au/ZNGs nanofluids increased remarkably due to synergistic effect. [ABSTRACT FROM AUTHOR]