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This paper presents numerical simulation of graphe nanoplatelet (GNP) – sodium dodecylbenzene sulfonate (SDBS) – water nanofluid with volumetric mass fractions of ϕ equal to 0–0.1%. The new microchannel is made of 2 layers and has sinusoidal cavities along with the heat sink. The study was conducted for Re = 50, 300, 700 and 1000 (laminar flow). Based on the results, higher Re leads to more convective heat transfer coefficient. Therefore, the value of temperature gradients decreases and on the other hand the effect of cooling fluid temperature in warm areas near solid wall becomes important. Using a higher value of Re results in the penetration of heat in the fluid layer decreases which in general will reduce the temperature of the outlet section in larger Re values. Also, larger Re value results in larger development length which is also a cause for lack of thermal development and dominance of the temperature of the coolant flow in the heat sink resulting in decreased outlet section temperature for higher Reynolds numbers. For Re = 50 and 300 because of lower fluid velocity, the effect of surface geometry factors such as sinusoidal paths or hollow parts (cavities) has a smaller influence on the pressure loss or friction factor of the flow. [ABSTRACT FROM AUTHOR]

Highlights • Anisotropic heat transfer and natural convection of a ferro-nanofluid are studied. • Based on frame indifference rule, anisotropic thermal conductivity tensor is derived. • Due to the magnetic field, the isotherms show significant anisotropy. • The Nusselt number increases significantly as the Rayleigh number increases. • The Hartmann number may enhance or diminish the thermal performance. Abstract In this paper, effects of anisotropic thermal conductivity and the Lorentz force in a ferro-nanofluid induced by external magnetic fields are investigated. The nanofluid is modeled as a non-linear single-phase fluid, where the viscosity is considered to depend on the nanoparticle concentration; the thermal conductivity shows anisotropy due to the existence of the magnetic field. The anisotropic thermal conductivity tensor, which depends on the magnetic field vector, is derived by considering the principle of material frame indifference of Continuum Mechanics. Numerical simulations are performed in a horizontal annulus enclosure. Effects of the nanoparticle concentration, magnetic distribution, and the dimensionless parameters, such as the Rayleigh number and the Hartmann number, are studied. The numerical results indicate that due to the anisotropic thermal conductivity, the isotherms become elliptic and deviate significantly from a circle which is a typical distribution with isotropic thermal conductivity; furthermore the elliptic shape changes as the direction of the magnetic field varies while the heat transfer is always much faster in the direction parallel to the magnetic field. For the range of the dimensionless parameters studied here, the Nusselt number increases significantly as the Rayleigh number (ranging from 2500 to 50,000) increases; depending on the situation, the magnetic field (the Hartmann number which ranges from 0 to 1) may enhance or diminish the thermal performance. In addition, the streamlines are more organized and less wavy when there exists a magnetic field; this could be attributed to the suppressive effect of the Lorentz force. [ABSTRACT FROM AUTHOR]

In the present paper, a numerical and experimental study has been performed to investigate the heat transfer and pressure drop properties of Al 2 O 3 and SiO 2 /Base oil nanofluid flow in a helical tube under constant heat fluxes. The nanofluids were prepared by using SN-300 base oil as a working fluid for 0.05%, 0.1%, 0.3%, and 0.5% mass concentrations. The experiments were carried out with two constant heat fluxes of 3950 W/m2 and 5280 W/m2 at 30, 40, 50, and 60 °C. The impact of various parameters, including flow Reynolds number, fluid temperature, two different nanoparticles, and various weight concentrations, on the heat transfer factor and pressure drop of the flow, are investigated. To examine the impact of different geometries on the heat transfer rate, simulations were conducted over four different helical tubes by changing the pitch circle diameter and steps. The results indicated that the heat transfer factor and pressure drop were increased by utilizing nanofluid instead of the base fluid. In addition, in the same mass concentration, the Al 2 O 3 nanofluid increased the heat transfer coefficient more than the SiO 2 nanofluid. The maximum heat transfer rate corresponds to 0.5% mass concentrations of Al 2 O 3 and SiO 2 nanofluids, which are 41.4% and 27.3% more than base oil, respectively. The helical tube compared to the straight tube increased heat transfer by 19.5%. Moreover, heat transfer was improved by 6% and 16.5%, respectively, by reducing helical pitch and pitch circle diameter. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, a three-dimensional analysis is used to study the heat transfer and entropy generation inside a helically coiled tube-in-tube heat exchanger in laminar flow regime using two different types of nanofluids. Overall heat transfer coefficient, effectiveness, Nusselt number, and entropy generation of helically coiled tube-in-tube heat exchanger were investigated considering the nanoparticle volume concentrations between 0 and 2.0 vol.%. The mass flow rate of the nanofluid from the inner tube was kept and the mass flow rate of the water from the annulus was set at either half, full, or double the value. The present contribution is a companion paper of Huminic and Huminic [1]. The numerical results reveal that the use of nanofluids in a helically coiled tube-in-tube heat exchanger improves the heat transfer performances. Thus, the maximum effectiveness was 91% for 2% CuO nanoparticles and 80% for 2% TiO 2 nanoparticles. Also, the increase of nanoparticles volume concentration leads to the Nusselt number increase and the reduction of the entropy generation due heat transfer effects, the viscous effects to entropy generation being negligible. [ABSTRACT FROM AUTHOR]

In this paper, heat transfer performance was experimentally tested in a helically coiled pipe using three types of nanofluids, TiO 2 , ZnO and Ag water-based nanofluids. TiO 2 , ZnO and Ag nanoparticles were characterized by X -ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). The XRD results showed that the purity of ZnO and TiO 2 were obtained. TEM and SEM results showed that the mean particles size of TiO 2 , ZnO and Ag are 14, 20 and 16 nm respectively. The three types of nanofluids, TiO 2 /water, ZnO /water and Ag /water were prepared with a volume concentration of 0.25%. To ensure a good mixture and measure particles distribution in each nanofluid, Zetsizer test was performed and showed a good distribution of nanoparticles in all tested nanofluids. The three different nanofluids have been thermally tested in helical coil with a flow rate from 1 to 3.5 L/s with different inlet temperatures in the range of 30 °C and 60 °C. The experimental results showed an enhancement in Nusselt number up to 27.31%, 16.03%, and 10.38% with augmentation in the heat transfer coefficient up to 32%, 21% and 16% utilizing TiO 2 , ZnO and Ag nanoparticles respectively. [ABSTRACT FROM AUTHOR]

In this paper, 3D analysis of forced convection of Newtonian and non-Newtonian nanofluids through a horizontal pipe using single- and two-phase mathematical models is performed. The models include the Newtonian single-phase model, non-Newtonian single-phase model, Newtonian two-phase mixture model and finally non-Newtonian two-phase mixture model. The geometry of the problem is a horizontal pipe that is filled with Al 2 O 3 /water nanofluid. The effects of particle volume fraction and the Reynolds number on the heat transfer and hydrodynamic characteristics of the flow are examined. Results indicate that for the volume fraction of 0.01, the non-Newtonian mixture model gives more accurate results in comparison with the other models. By increasing the solid volume fraction, the mixture models give a higher heat transfer coefficient in comparison with that of the corresponding single-phase model; however, by comparing the results of Newtonian and the corresponding non-Newtonian models, no meaningful relationship can be obtained. Furthermore, for all the investigated models, the Nusselt number is increased with increasing the Reynolds number. [ABSTRACT FROM AUTHOR]

• Heat transfer performance of nanofluids in a plate heat exchanger is investigated. • The maximum enhancement in average Nu is 22.6% for 1.0 wt.% Fe 3 O 4 -water nanofluid. • The optimum concentration for thermal enhancement is 0.5 wt.% for CuO nanofluid. • Empirical formulas of experimental Nu are derived based on experimental data. • Fe 3 O 4 -water nanofluid is a promising heat transfer medium for solar energy systems. In this paper, a corrugated plate heat exchanger in solar energy systems is used to investigate heat transfer and fluid flow characteristics of various nanofluids. By adding various nanoparticles (Al 2 O 3 -30 nm, SiC-40 nm, CuO-30 nm and Fe 3 O 4 -25 nm) into the base fluid, effects of nanofluid types and particle concentrations (0.05 wt.%, 0.1 wt.%, 0.5 wt.% and 1.0 wt.%) on the thermal performance of the plate heat exchanger are analyzed at flow rates in the range of 3–9 L/min. Results indicate that both heat transfer enhancement and pressure drop for nanofluids show significant increases compared to the base fluid. The Fe 3 O 4 -water and CuO-water nanofluids show the best and the worst thermal performances of the plate heat exchanger, respectively. When 1.0 wt.% Fe 3 O 4 -water nanofluid is used as the working fluid, compared to DI-water, the convective heat transfer coefficient is increased by 21.9%. However, an increase of 10.1% in pressure drop is obtained for the 1.0 wt.% Fe 3 O 4 -water nanofluid. Finally, empirical formulas of experimental Nusselt number are obtained based on the experimental data. A new way to predict the thermal performance for various nanofluids in heat transfer systems is provided. [ABSTRACT FROM AUTHOR]

In this paper, an experimental investigation is carried out on internal convective heat transfer of SiO 2 /water nanofluids in a copper tube for a fully turbulent regime. Nusselt number and convective heat transfer coefficients of nanofluid at three different volumetric concentration (0.001%, 0.003%, 0.007%) of nanoparticles were estimated. Local convective heat transfer coefficient at different locations along the tube at varying Reynolds number was also observed. With volumetric concentration of 0.001% of SiO 2 nanoparticles, maximum enhancement observed was 8–9%. Whereas at 0.007% volumetric concentration of SiO 2 nanoparticles, a 27% enhancement in convective heat transfer coefficient was observed. The decrease in the heat transfer rate was observed in axial direction. Particle migration, chaotic movement of the nanoparticles and fluctuations in the fluid and increased thermal conductivity of the nanofluid are considered the possible reasons for this enhancement. • Internal convective heat transfer of SiO 2 /water nanofluid • Heat transfer coefficient at 0.001, 0.003 and 0.007 vol% of nanoparticles • Local convective heat transfer at different locations along the tube • Average and local Nusselt number at different locations along the tube • 0.007% SiO 2 nanofluid shows almost 27% enhancement in heat transfer. [ABSTRACT FROM AUTHOR]