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[en] Nanofluid slip flow with distinct solid particles past a wedge with convective surface and high order slip is discussed in this paper. The wedge model is modified by considering the effects of Brownian motion and thermophphoresis together with the high order velocity slip and temperature jump. In this study, the governing fundamental equations are first transformed into third-order ordinary differential equations and solved by using the homotopy analysis method (HAM). Through error analysis and comparison with previous research, the effectiveness of HAM is ascertained, and the crucial influence of nanoparticles and high-order slip on the fluid skin-friction coefficient and heat transfer coefficient is analysed. Thermophphoresis parameter and suction/injection parameter are found to cause an increase in velocity and temperature. The rate of heat transfer in the Cu-water nanofluid is found to be higher than the others. (author)
[en] Magnetic nanofluids are colloidal mixtures of ferromagnetic nanoparticles dispersed in a base fluid. They can be actuated and manipulated under the influence of the external magnetic field. This makes them especially attractive to be employed in microfluidics and nanofluidics. In the presence of the external magnetic field, thermal conductivity and viscosity of the magnetic nanofluids can be tuned, hence magnetic field dependent thermal conductivity and viscosity measurements have become a hot topic for the researchers. In this paper, studies in the available literature on the thermal conductivity and the viscosity of the magnetic nanofluids in the presence of the magnetic field have been collected, compared and discussed. The observations reveal that there is a contradiction between the results which were presented in the literature. The differences between the available experimental results which may be caused by the application of the external magnetic field have been discussed by categorizing and comparing the studies which investigated the influence of the similar parameters by using most similar samples. Additionally, magnetic field dependent thermal conductivity and viscosity models available in the literature have been reviewed. (topical review)
[en] This study examines the thermal behavior of a hemispherical electronic component subjected to a natural nanofluidic convective flow. During its operation, this active dome generates a high power, leading to Rayleigh number values reaching 4.56×109 . It is contained in a hemispherical enclosure and the space between the dome and the cupola is filled with a monophasic water-based copper nanofluid whose volume fraction varies between 0 (pure water) and 10%. According to the intended application, the disc of the enclosure may be tilted at an angle ranging from 0° to 180° (horizontal disc with dome facing upwards and downwards, respectively). The numerical solution has been obtained by means of the volume control method. The surface average temperature of the dome has been determined for many configurations obtained by combining the Rayleigh number, the cavity’s tilt angle and the nanofluid volume fraction which vary in wide ranges. The temperature fields presented for several configurations confirm the effects of natural convection. The results clearly highlight the effects of these influence parameters on the thermal state of the assembly. The study shows that some combinations of the Rayleigh-tilt angle-volume fraction are incompatible with a normal operating system at steady state and that a thermoregulation is required. The correlation of the temperature-Rayleigh-Prandtl-angle type proposed in this work allows to easily carry out the thermal dimensioning of the considered electronic assembly.
[en] The evaporation of the nanofluids based on Al2O3 nanoparticles and different fluids was experimentally investigated. The distilled water and isopropyl alcohol were used as base fluids. The average diameter of Al2O3 particles was 100 nm. The investigations of fluids evaporation rates were carried out using the Simultaneous Thermal Analyzer STA 449 C Jupiter (NETZSCH). The investigation of the evaporation rate dependence on the carrier media was carried out. It was found that the average relative evaporation rate of fluids increased, and the time of complete evaporation accordingly decreased with an increase in the volume concentration of nanoparticles. In addition, the absolute value of the evaporation rate was found to significantly depend on the type of base fluid. However, the relative value of the evaporation rate for different base fluids remains approximately the same. (paper)
[en] In the present work, an investigation on the relationship between clustering phenomenon and thermal conductivity of nanofluids is presented. Particularly, an experimental campaign was carried out to correlate mean dimension of cluster, ranging from 168 to 20,933 nm, to nanofluid’s thermal behavior. A further objective of this study was to evaluate how the stability of nanofluid can affect thermal conductivity measurements, carried out by means of hot-wire technique. Experimental results showed that thermal conductivity, measured at constant volume concentration of nanoparticles as a function of cluster dimension, first decreases and then augments, as it was under a dual effect: negative in case of small clusters and positive with big clusters within nanofluid. Actually, further measurements of zeta potential and backscattered light demonstrated that clustering reduces nanofluid’s thermal conductivity, while its increment can be related to sedimentation of clusterized particles, which produces convective motion around the hot wire, generating overestimated measurements.
[en] Highlights: • Synthesis of XC-treated GNPs using simple and economical method was successful. • High stability of XC-treated GNPs nanofluids were recorded after 15 days. • XC-treated GNPs nanofluids shows good performance for thermophysical properties. • A potentially material to be used in thermal applications was introduced.
[en] Highlights: • Au, Au/Pt and Au/Pt/Ag nanofluids were prepared by microwave irradiation method. • The Au/Pt/Ag nanofluid revealed an alloy core surrounded by metallic shell. • Antibacterial activity was evaluated by MIC and zone inhibition. • Trimetallic Au/Pt/Ag showed superior biocidal activity compared to Au and Au/Pt.
[en] In the current study, sway of nanofluid on peristaltic transport of a hyperbolic tangent fluid model in the incidence of tending magnetic field has been argued. The governing equations of a nanofluid are first modeled and then simplified under lubrication approach. The coupled nonlinear equations of temperature and nano particle volume fraction are solved analytically using a homotopy perturbation technique. The analytical solution of the stream function and pressure gradient are carried out using perturbation technique. The graphical results of the problem under discussion are also being brought under consideration to see the behavior of various physical parameters. - Highlights: • The main motivation of this work is that we want to see the behavior of nanofluids in peristaltic flows. • In literature few articles are available on this, but no article is available in asymmetric channel on the new fluid model hyperbolic tangent fluid. • So we want to fill the gap in literature studying this
[en] A numerical approach is adopted to explore the analysis of combined convection and thermal radiation on molecular theory of liquid originated nanofluid over an extendable surface. The temperature-dependent viscosity is considered through Vogel’s and Renold’s model. The physical problem gains more significance in the presence of temperature-dependent thermal conductivity. Nanofluid attributes are explored through thermophoresis and Brownian motion effect. Radiative heat flux is also taken into account to study the thermal radiation aspects. Characteristics of sundry physical parameters on the velocity, thermal energy and mass transfer are computed numerically and graphically. Velocity pattern expands for growing the size of thermophoresis diffusion and decline by the expanding amount of fluid parameter for Vogel’s and Renold’s model. Temperature fluctuation rises when the quantity of variable thermal conductivity parameter getting up and falls for radiation parameter. Concentration curve increases if the values of Prandtl number enlarge for Renold’s model. Concentration boundary layer thickness declines for inclining in Brownian diffusion, radiation and Prandtl number for Vogel’s model. (paper)