Dynamic Conductivity Research Articles

Mixed Convection of Hybrid Nanofluid in Inclined Annulus Subjected to Solar Radiation

The problem investigated in this paper consists of the mixed convection of the Ag–ZnO (50%–50%)/water hybrid nanofluid in an inclined annular space; the upper part of the outer wall is exposed to solar radiation. Based on experimental data, new temperature-dependent expressions have been developed in this work to calculate dynamic viscosity and thermal conductivity. The governing equations were solved using the Fluent solver based on the finite volume method. Results show that Ag–ZnO/water has the highest Nu number compared to pure water and ZnO/water for all studied values of Ri number (0.3, 0.7, 1, 1.3, 1.7, 2) and volume concentration (0.01 and 0.02). However, the volume concentration effect on the friction coefficient is negligible for less than 0.15. Inhomogeneous solar radiation distribution at the wall has a very strong effect on the variation of the dynamic and thermal quantities. Temperature variations are more important above the horizontal diameter. In addition, the secondary flow has a direct impact on velocity variations. This effect results in the appearance of two symmetric vortices above the horizontal diameter. Vortices velocity increases with the Ri number increase. Considering tilt angle, obtained results show that its effect on dynamic quantities is more important.

An improved correlation for thermophysical properties of binary liquid mixtures

This paper presents an improved correlation for thermophysical properties of binary mixtures. The new correlation permits calculation of excess properties and property deviations, and it has the capability of correlating and predicting different functional forms of the thermophysical properties within the experimental uncertainties. This paper contains examples for: molar volume, kinematic and dynamic viscosity, surface tension, refractive index, heat capacity and thermal conductivity.

On the mathematical model of Eyring–Powell nanofluid flow with non-linear radiation, variable thermal conductivity and viscosity

It is well known that the significance of dynamic viscosity and thermal conductivity cannot be overemphasized in the movement of any fluid. In the present investigation, the impact of variable viscosity, variable thermal conductivity, Brownian motion, thermophoresis, heat and chemical reaction effects on an unsteady Eyring–Powell nanofluid flow in a stretching sheet is extensively discussed. The governing non-linear coupled partial differential equations describing the problem were derived. Similarity variables were used to transform the governing partial differential equations into ordinary differential equations. After which the Spectral quasi-linearization method (SQLM) was employed to numerically handle the emerging governing differential equations after validating the convergence of the method with existing results in literature. The novel flow features which include fluid velocity, skin friction, heat transfer coefficient and rate of mass transfer were discussed therein as a function of sundry parameters entering flow formation. Findings reveal that the Brownian motion and thermophoresis parameters increase the temperature profile. Also, fluid concentration was found to be a decreasing and increasing function of Brownian motion parameter and thermophoresis parameter respectively. For accuracy check, tabular representations are carried out with published work in the literature; excellent agreement were found.

Influence of Nanoparticle Shapes of Boehmite Alumina on the Thermal Performance of a Straight Microchannel Printed Circuit Heat Exchanger

The efficiency and irreversibility defined based on the second law ofthermodynamics provide a new path for heat exchangers design and makeperformance analysis more straightforward and elegant. The second lawof thermodynamics is applied in a Straight Microchannel Printed Circuitheat exchanger to determine the thermal performance of different shapes ofBoehmite Alumina compared to Al2O3 aluminum oxide. The various formsof non-spherical Boehmite Alumina are characterized dynamically andthermodynamically through dynamic viscosity and thermal conductivity,using empirical coefficients. The non-spherical shape includes platelet,cylindrical, blades, and bricks forms. Graphical results are presented forthermal efficiency, thermal irreversibility, heat transfer rate, and nanofluidexit temperature. The non-spherical shapes of Boehmite Alumina showdifferent thermal characteristics concerning the spherical shape whenthere are variations in fluid flow rates and the nanoparticles fraction.Furthermore, it was theoretically demonstrated that non-spherical particleshave higher heat transfer rates than spherical particles, emphasizingplatelets and cylindrical shapes for the low volume fraction of nanoparticlesand bricks and blades for high volume fraction.

Hybrid nanocellulose/carbon nanotube/natural rubber nanocomposites with a continuous three‐dimensional conductive network

AbstractIn this study, the hybrid effect of nanocellulose/carbon nanotube (NCC/CNT) reinforcement on natural rubber (NR) nanocomposites was investigated. To this end, three series of NR nanocomposites were prepared: NCC/NR, CNT/NR and NCC/CNT/NR. First, the nanocomposites morphology and the filler–rubber interactions were studied using scanning electron microscopy (SEM) and the swelling behavior in toluene, respectively. The results showed that the presence of NCC improved the NCC/CNT hybrid filler dispersion forming a 3D network, while the presence of CNT increased the filler–matrix interaction. The curing results also confirmed that the degree of crosslinking increased when hybrid fillers were used, but the curing time was not modified. In addition, it was observed that using a NCC/CNT hybrid system led to superior mechanical properties, dynamic mechanical properties and thermal conductivity than each material used separately. When 10 phr hybrid filler (with a filler ratio of 1) was added to NR, the tensile strength, modulus at 300% elongation (M300), storage modulus at 10% strain and thermal conductivity were all increased by 57%, 137%, 120%, and 30%, respectively. The results also showed that the NR nanocomposites properties can be controlled by tuning the NCC/CNT filler ratio.

The Potential for the Direct and Alternating Current-Driven Electrospinning of Polyamides.

The paper provides a description of the potential for the direct current- and alternating current-driven electrospinning of various linear aliphatic polyamides (PA). Sets with increasing concentrations of selected PAs were dissolved in a mixture of formic acid and dichloromethane at a weight ratio of 1:1 and spun using a bar electrode applying direct and alternating high voltage. The solubility and spinnability of the polyamides were investigated and scanning electron microscopy (SEM) images were acquired of the resulting nanofiber layers. The various defects of the spun fibers and their diameters were detected and subsequently measured. Moreover, the dynamic viscosity and conductivity were also subjected to detailed investigation. The most suitable concentrations for each of the PAs were determined according to previous findings, and the solutions were spun using a NanospiderTM device at the larger scale. The fiber diameters of these samples were also measured. Finally, the surface energy of the fiber layers produced by the NanospiderTM device was measured aimed at selecting a suitable PA for a particular application.

Controllable nonreciprocal optical response and handedness-switching in magnetized spin-orbit coupled graphene

Starting from a low-energy effective Hamiltonian model, we theoretically calculate the dynamical optical conductivity and permittivity tensor of a magnetized graphene layer with Rashba spin orbit coupling (SOC). Our results reveal a transverse Hall conductivity correlated with the usual nonreciprocal longitudinal conductivity. Further analysis illustrates that for intermediate magnetization strengths, the relative magnitudes of the magnetization and SOC can be identified experimentally by two well-separated peaks in the dynamical optical response (both the longitudinal and transverse components) as a function of photon frequency. Moreover, the frequency dependent permittivity tensor is obtained for a wide range of chemical potentials and magnetization strengths. Employing experimentally realistic parameter values, we calculate the circular dichroism of a representative device consisting of magnetized spin orbit coupled graphene and a dielectric insulator layer, backed by a metallic plate. The results reveal that this device has different relative absorptivities for right-handed and left-handed circularly polarized electromagnetic waves. It is found that the magnetized spin orbit coupled graphene supports strong handedness-switchings, effectively controlled by varying the chemical potential and magnetization strength with respect to the SOC strength.

Experimental study and computational intelligence on dynamic viscosity and thermal conductivity of HNTs based nanolubricant

PurposeThis paper aims to evaluate the dynamic viscosity and thermal conductivity of halloysite nanotubes (HNTs) suspended in SAE 5W40 using machine learning methods (MLMs).Design/methodology/approachA two-step method with surfactant was selected to prepare nanolubricants in concentrations of 0.025, 0.05, 0.1 and 0.5 wt%. Thermal conductivity and dynamic viscosity of nanofluids were ascertained over the temperature range of 25–70 °C, with an increment step of 5 °C, using a KD2-Pro analyser device and a digital viscometer MRC VIS-8. Additionally, four different MLMs, including Gaussian process regression (GPR), artificial neural network (ANN), support vector machine (SVM) and decision tree (DT), were used for predicting dynamic viscosity and thermal conductivity by using nanoparticle concentration and temperature as input parameters.FindingsAccording to the achieved results, the dynamic viscosity and thermal conductivity of nanolubricants mostly increased with the rise of nanoparticle concentration in the base oil. All the proposed models, especially GPR with root mean square error mean values of 0.0047 for dynamic viscosity and 0.0016 for thermal conductivity, basically showed superior ability and stability to estimate the viscosity and thermal conductivity of nanolubricants.Practical implicationsThe results of this paper could contribute to optimising the cost and time required for modelling the thermophysical properties of lubricants.Originality/valueTo the best of the author’s knowledge, in this available literature, there is no paper dealing with experimental study and prediction of dynamic viscosity and thermal conductivity of HNTs-based nanolubricant using GPR, ANN, SVM and DT.

Properties of water-based fly ash-copper hybrid nanofluid for solar energy applications: Application of RBF model

The hybrid nanofluids were used as absorber fluids in solar energy applications, which could further increase the efficiency of solar devices. The use of nanofluids in solar devices with the laminar and turbulent flow has received much attention. Presently, the effect of temperature and concentration on thermal conductivity and viscosity of fly ash-copper (80:20% by volume) hybrid nanofluid is investigated. The thermal conductivity and viscosity measurements were carried in the temperature range of 30–60 °C for a concentration range of 0–4.0 vol%. The nanoparticles and nanofluids were characterized by XRF, XRD, SEM, TEM, zeta potential, and DLS techniques. The maximum augmentation in the hybrid nanofluid's dynamic viscosity and thermal conductivity at a concentration of 4 vol% is 45.18% and 49.8%, respectively, at 30 and 60 °C. Correlations to estimate the hybrid nanofluid's dynamic viscosity and thermal conductivity have been proposed considering the results obtained from the present study. A radial basis function-based neural network is used to model nanofluids' effective thermal conductivity and relative viscosity. The outcomes of the experiments were used to calculate the Mouromtseff number and heat transfer efficiency for solar energy applications. • HyNF shows Newtonian behavior in the studied range. • The maximum augmentation in viscosity is 45.2%. • The highest amplification in thermal conductivity is 49.8%. • Radial basis function based neural network was used.

Ethyl-, vinyl- and ethynylcyanoborates: room temperature borate ionic liquids with saturated and unsaturated hydrocarbon chains.

Ethyl-, vinyl- and ethynyltricyano and dicyanofluoroborates were prepared on a gram scale from commercially available potassium trifluoroborates and trimethylsilylcyanide. Salt metathesis resulted in the corresponding EMIm-salts that are hydrophobic room-temperature ionic liquids (RTILs). The new RTILs exhibit unprecedented large electrochemical windows in combination with high thermal stabilities, low dynamic viscosities and high specific conductivities. These properties make them promising materials, especially for electrochemical applications.

Intrinsic toughened conductive thermosetting epoxy resins: utilizing dynamic bond and electrical conductivity to access electric and thermal dual-driven shape memory

Epoxy resins are currently the most widely used thermosetting polymers due to their high thermal stability, excellent electrical insulation, and chemical resistance.

FULLY DEVELOPED TEMPERATURE PROFILE FOR A POWER-LAW LAMINAR NANOFLUID FLOW IN A CIRCULAR DUCT SUBJECT TO A UNIFORM HEAT FLUX

In the present work, we develop a theoretical analysis of a fully developed laminar nanofluid flow in a circular duct in steady state, subject to a uniform heat flux condition. The rheological behavior of the base fluid is described by the power-law model and the nanofluid properties such as dynamic viscosity, thermal conductivity, density and specific heat are assuming as constants for a fixed value of the volumetric fraction. An analytical solution can be obtained by the mean temperature concept. The Nusselt number was defined and depends on the dimensionless parameter of the viscosity and the power-law index. The main results reveals that, for a maximum value of the volumetric fraction, the Nusselt number decreases drastically for shear-thinning base fluids, for shear-thickenning base fluids tends asymptotically to a constant value. For an increase in the volumetric fraction value, the dimensionless velocity profiles shown lower values for shear-thinning base fluids and the dimensionless temperature profiles showed a greater difference between the dimensionless wall temperature and the nanofluid stream temperature.

Real-fluid thermophysicalModels: An OpenFOAM-based library for reacting flow simulations at high pressure

Although OpenFOAM is a widely-used open source computational fluid dynamics (CFD) tool, it is limited to numerical simulations of multi-dimensional reacting/nonreacting flows at relatively-low pressures. This is not only because real-fluid models that can evaluate thermophysical properties at high pressures are not available in the thermophysicalModels library of OpenFOAM, but also because the existing mixing model cannot handle various mixing rules of real-fluid models. In the present study, we develop a novel algorithm applicable for a mixture model incorporating various mixing rules in OpenFOAM. Based on the new algorithm, we update the thermophysicalModels library of OpenFOAM 6.0 by implementing a set of real-fluid models such as the Soave-Redlich-Kwong/Peng-Robinson equation of state, Chung's model for dynamic viscosity and thermal conductivity, mixture averaged model for mass diffusivity using Takahashi's correction for binary diffusion coefficients at high pressure. The new library is validated against experimental data and is further assessed for compressible reacting flows by performing two-dimensional numerical simulations of axisymmetric laminar non-premixed counterflow flames and one-dimensional numerical simulations of premixed CH4/air flames at high pressures. The developed library can be used for any reacting flow solvers in OpenFOAM 6.0 that adopt a set of implemented real-fluid models. Program summaryProgram title: Real-fluid thermophysicalModelsCPC Library link to program files:https://doi.org/10.17632/n8zb2wpjp6.1Developer's repository link:https://github.com/danhnam11/realFluidThermophysicalModels-6Licensing provisions: GPLv3Programming language: C++Nature of problem: The mixing rules required for evaluating the real-fluid based thermophysical properties of mixtures are relatively complicated and different from each other, while the existing thermophysicalModels library offers only a mixing rule based on the mass fraction weighted average of each species, for which overloading operator functions (“*” and “+=”) are utilized to update parameters for a mixture. However, this approach is not applicable for complicated mixing rules in the real-fluid models.Solution method: To build a mixture class containing different mixing rules in different models such as the equation of states and thermodynamics/transport properties in OpenFOAM, we adopt void-type functions (parameter updating functions) to update parameters of a mixture instead of the original overloading operator functions in OpenFOAM. The parameters in the mixing rules that depend on pressure and temperature are handled by decomposition such that they can be updated in the mixture class.

Transport on the ferromagnetic Lieb lattice

Each unit cell on the Lieb lattice contains three atoms, and its energy spectrum has a three-band structure, with a flat band touching two dispersive bands at a single point. A Dzyaloshiskii-Moriya term does not affect the flat band. Still, it opens the gap between the flat and upper and lower dispersive bands generating a nontrivial intrinsic Berry phase that leads to topological features of spin transport. A nonzero Berry curvature leads to a spin current perpendicular to an applied magnetic field or temperature gradient. The lattice is of great interest because several materials have their atoms arranged on the Lieb lattice. We calculate the transverse spin Hall conductivity, the spin Nernst coefficient, the dynamical longitudinal spin conductivity, and the Drude weight.

Effect of highly thermally conductive Ag@BN on the thermal and mechanical properties of phthalonitrile resins

Ag@BN/phthalonitrile resin composites were prepared using highly thermally conductive BN modified by Ag plating. The effects of different contents of Ag@BN particles on the dynamic mechanical properties, thermal stability, and thermal conductivity of composites were examined. The results of Fourier-transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy analyses showed that Ag was successfully deposited on the surface of BN. The prepared Ag@BN was subjected to KH550 grafting treatment. With the increase in the content of Ag@BN/KH550, the storage modulus, thermal stability, and thermal conductivity of the composite increased. The storage modulus, decomposition temperature, and thermal conductivity of the Ag@BN/phthalonitrile composite with 20 wt.% Ag@BN/KH550 were 5.0 GPa, 539°C, and 0.80 W/(mK), respectively, which are 1.35, 1.18, and 3.33 times higher than those of pure resin, respectively. The compatibility and dispersibility of BN modified by Ag plating in phthalonitrile resin were effectively enhanced, thereby providing a potential candidate to be used at high-temperature devices with high thermal conductivity.

A fully analytical solution of convection in ferrofluids during Couette-Poiseuille flow subjected to an orthogonal magnetic field

We report the transport of thermal energy during a hydrodynamically as well as thermally developed Couette-Poiseuille flow of ferrofluid (FF) through parallel-plate channels subjected to a constant magnetic field, orthogonal to the channel axis. The fluid motion is imparted by a combination of tangential stress, attributable to the motion of one of the plates, and a constant pressure gradient present in the direction of the channel axis. Apart from imparting a body force and torque, the application of an external magnetic field increases both the dynamic viscosity and effective thermal conductivity of the FF. As a result, thermal energy transport is uniquely affected. The complex coupling of magnetics with hydrodynamics results in implicit governing equations, which cannot be solved analytically in their full form. On the basis of logical reasoning, the governing equations are simplified to generate closed-form solutions of temperature profiles and Nusselt numbers. For a comprehensive study, we consider three different sets of thermal boundary conditions amenable to analytical solutions. Till the saturation of magnetization, we observe an increase in the local temperature as the strength of the applied magnetic field increases. The effects of particle loading in FF, Brinkman number, and heat flux ratio on the temperature field are also discussed.

Production performance analysis of multi-fractured horizontal well in shale gas reservoir considering space variable and stress-sensitive fractures

Multi-stage fracturing technology makes shale gas production economically viable. In this paper, an innovative model incorporating space variable and stress-sensitive fractures is established for the production of MFHW in shale. Multi-transport mechanisms including Darcy flow, Knudson diffusion, Surface diffusion are considered in the mathematical model. Three space variable conductivity patterns (Linear, Exponential, and Logarithmic variations) are introduced and adopted. Based on the discretization method, a novel method is proposed which can simulate uniform and space varying fractures conveniently. Then the semi-analytical solution is obtained by Stehfest numerical inversion and an iteration method. And good agreements with previous models are observed in the validation. Afterward, the pressure transient type curve is generated and eight flow periods are identified. Subsequently, the influences of several vital parameters are discussed in detail. The results show that space varying fracture enlarges the pressure drop and decreases the productivity of early time. Such an effect is enhanced as the space variable coefficient is increased. And this influence decreases with the increase of initial conductivity. Considering stress-sensitive fractures, a ‘hump’ appears in the pressure derivative curve and the early time productivity decreases. A bigger stress-sensitive coefficient accelerates the appearance of the ‘hump’ and makes the ‘hump’ sharper. The ‘hump’ and productivity decline caused by dynamic conductivity becomes more obvious with the decrease of the minimum conductivity. Complex transport mechanisms enhance inter-porosity flow. The inter-porosity flow would appear earlier with complex transport mechanisms. The model can simulate the gas flow of MFHW more realistically. It can help for better understanding of the production dynamic of MFHW in shale. • A semi-analytical approach is established for the pressure and rate transient of MFHW in shale gas reservoir. • Space variable and stress-sensitive fractures and multi-transport mechanisms of shale gas are considered. • A new solution and an iteration method are utilized to solve the space varying fracture and nonlinear problem. • Effects of some vital parameters on production performance are analyzed.

The paradox of heat conduction, influence of variable viscosity, and thermal conductivity on magnetized dissipative Casson fluid with stratification models

The boundary layer flow of temperature-dependent variable thermal conductivity and dynamic viscosity on flow, heat, and mass transfer of magnetized and dissipative Casson fluid over a slenderized stretching sheet has been studied. The model explores the Cattaneo-Christov heat flux paradox instead of the Fourier’s law plus the stratifications impact. The variable temperature-dependent plastic dynamic viscosity and thermal conductivity were assumed to vary as a linear function of temperature. The governing systems of equations in PDEs were transformed into non-linear ordinary differential equations using the suitable similarity transformations, hence the approximate solutions were obtained using Chebyshev Spectral Collocation Method (CSCM). Effects of pertinent flow parameters on concentration, temperature, and velocity profiles are presented graphically and tabled, therein, thermal relaxation and wall thickness parameters slow down the distribution of the flowing fluid. A rise in Casson parameter, temperature-dependent thermal conductivity, and velocity power index parameter increases the skin friction thus leading to a decrease in energy and mass gradient at the wall, also, temperature gradient attain maximum within 0.2 - 1.0 variation of Casson parameter.

Electrical conductivity of Sn at high pressure and temperature

To date, temperature and conductivity have many outstanding implications in extreme environments but are yet to be fully understood under high pressure and temperature dynamic conditions. Here, we introduce an approach to provide high quality electrical conductivity results under dynamic loading conditions. Emphasis is given to address the skin depth effect's influence in a dynamic loading experiment by using thin films. The thin film samples in this study were at least 100 times thinner than previous samples in dynamic electrical conductivity experiments, increasing the current density to its full potential across the sample's entire cross section. Consideration of the skin depth accounts for at minimum a $4\ifmmode\times\else\texttimes\fi{}$ scaling factor to the final electrical conductivity result that has been neglected in previous dynamic electrical conductivity studies. We also obtained improved signal-to-noise ratio with custom diagnostics optimized for better electrical impedance matching. These considerations were applied to Sn to assess electrical conductivity at elevated pressure and temperature. The high signal-to-noise ratio with reduced skin depth influence results in Sn allowing observation of the conductivity changes related to solid-to-solid and solid-to-liquid phase transitions. Additionally, we calculate the Sn thermal conductivity using the Wiedemann-Franz law for our experiments and compare against thermal transport dependent temperature measurements from previous work.

Comparison of analysis methods for determination of dynamic tissue conductivity during microseconds-long pulsed electric fields

Objective: High-frequency irreversible electroporation (H-FIRE) is an emerging therapy which uses bursts of high-voltage, bipolar pulses to ablate tissue. This paper aims to quantify electric-field-dependent material properties of select tissues for computational models. The results show that tissues treated with 5 and 10 μs H-FIRE can be approximated as purely resistive, simplifying analysis and numerical modeling. Methods: Parallel-plate electrodes were used to apply H-FIRE waveforms (5-5-5 and 10-1-10) to samples of porcine pancreas, liver, prostate, brain, and patient-derived prostate tumor. Resistance of each sample during pulsing was calculated from captured current waveforms using two methods for comparison: one assuming a purely resistive response from tissue and the other assuming dispersion. Results: Conductivity versus electric field (EF) behavior is reported for all five tissue types. There was little dependence of conductivity on EF magnitude for most tissues except for prostate and prostate tumor tissue. Additionally, the study found that differences between the two resistance analysis methods were less than 10% except for prostate (<30%) and liver and pancreas at lower EF magnitudes. Conclusion: Prostate and prostate tumor tissues are expected to undergo more EF redistribution during H-FIRE as compared with the other tissues. Also, in most cases under study, the results suggest that frequency effects are minimal using these particular waveforms. Significance: Currently, high-frequency effects on tissue properties that occur during microseconds-long bipolar pulses are not yet clear and quantified. This work reports these properties while also assessing whether approximation of the tissue as resistive is appropriate.