Dynamic Conductivity Research Articles

Productivity-Index Behavior for a Horizontal Well Intercepted by Multiple Finite-Conductivity Fractures Considering Nonlinear Flow Mechanisms under Steady-State Condition

In this paper, a mathematical model is proposed to investigate the effect of nonlinear flow mechanisms on productivity-index (PI) behavior in hydraulically fractured reservoirs during steady-state condition. This approach focuses on the fact that PI approaches a constant value at a certain time, indicating the beginning of steady state. In this model, the reservoirs are considered as an elliptical-shaped drainage with constant-pressure boundary, which is depleted by a multiple-fractured horizontal well (MFHW), and various nonlinear flow mechanisms, such as the non-Darcy flow effect and pressure-dependency effect, control flow patterns in the hydraulic fractures. Then, an exact algorithm of solving the resulting nonlinear equations is developed to obtain the PI of MFHW using a semi-analytical approach. Next, type curves are generated to investigate the influences of flow mechanisms and fracture properties on PI. The most interesting points in this study are the following: (1) PI is determined by the properties of MHFW (i.e., dimensions and configuration), the reservoir geometry, and flow mechanism; (2) PI is deteriorated by non-Darcy flow caused by inertial forces; and (3) PI is reduced under the influence of pressure sensitivity caused by the degradation of dynamic conductivity. Generally, this study provides a significant insight into understanding the factors affecting the productivity of a MFHW with nonlinear flow mechanisms.

Non-Parabolicity correction for fifty-nine solvents and a retention study for strongly distorted flow-profiles in thermal field-flow fractionation

The non-parabolicity correction of the laminar flow profiles was numerically calculated for fifty-nine solvents. The exact flow profiles were simulated based on sophisticated experimental literature data of dynamic viscosity and thermal conductivity and their dependency on the temperature in between cold wall temperatures of –10 °C up to 120 °C and temperature gradients up to ΔT = 120 K. Based on this computation the polynomial coefficients for the calculation of the non-parabolicity parameter ν is tabulated for each solvent. For this calculation a third-degree polynomial velocity profile was applied, which approximates in a good agreement the exact profile for moderately distorted flow profiles. Instead, for strongly distorted flow profiles a more exact solution with keeping ν as only adjustable parameter is proposed. Additionally, an empirically derived solution is presented to calculate the dimensionless retention parameter λ in fair accuracy directly from retention data.

Dual-MRT lattice Boltzmann method combined with experimental measurements of nanofluid’s properties for analysis of fin-orientation effect on natural convection heat transfer

Purpose Natural convection heat transfer during free convection phenomenon in a cavity included with active fins and pipes is investigated. The influence of the orientation of fins on the heat transfer between heat source (i.e. hot fins) and heat sink (i.e. cold pipes) is investigated by using numerical and experimental techniques. Design/methodology/approach For the numerical simulations, the multiple relaxation time (MRT) thermal lattice Boltzmann method (LBM) is used. In this numerical approach, two separated distribution functions are used to solve the flow and temperature distributions within the computational domain. Furthermore, the local/volumetric second law analysis is used to show the impact of evaluated parameters on the heat transfer irreversibility. In addition, the dynamic viscosity and thermal conductivity of TiO2-water nanofluid are measured by using Brookfield viscometer and KD2 pro conductmeter, respectively. Findings The examined range of Rayleigh number is from 103 to 106, and the nanofluid samples are provided in 0, 20, 40, 60, 80 and 100 ppm. Originality/value The originality of this work is use of dual-MRT thermal LBM and experimental measurements of rheological/thermal properties of nanofluid for investigation of free convection problem for the considered application.

A hierarchy of macroscopic models for phonon transport in graphene

In this work, we propose a hierarchy of macroscopic models for the description of phonon transport in graphene. They are devised starting from the phonon Boltzmann transport equation by using the moments method and the maximum entropy principle. The state variables are the phonon energy densities and the fluxes of integer powers of the energy. We underline that the full energy dispersion relations are used. We test the validity of the models by analysing the steady-state and dynamical thermal conductivity, and the heat transport in zigzag and armchair graphene nanoribbons under a fixed temperature gradient.

Analysis of Dynamical Heat Conductivity of the Reservoir and Fluid Evacuation Zone on the Gas Condensate Well Flow Rate

This study shows that the thermal conductivity of the rock borehole adjacent to the wells varies depending on the operation of the well. This is due to the fact that the actual temperature and temperature difference affect the humidity and other thermal properties of the rocks, which in turn affect the heat transfer coefficient across the section between the moving gas and the rocks. The static temperature field of primitive geothermal gradients acquires changes in a dynamic form. Theoretical consideration of changes in the thermal conductivity of rocks near the face and the wells is proposed to improve the prediction of gas condensate wells production. The result is achieved by introducing the specified equations of the thermal energy balance in the radial filtration and lifting of well products, which contain the coefficients of heat exchange and throttling. The refinement bias estimation of the 10%–15% level of gas condensate well extraction is shown using proposed methodological approach to relatively well-known (traditional in the field development practice) methods for estimating the extraction of a “medium well” from a particular oil and gas field evaluation. The results of this work demonstrate important scientific, applied, educational and methodological significance of using the methodology presented by the authors.

Presenting two new empirical models for calculating the effective dynamic viscosity and thermal conductivity of nanofluids

In this paper, two new empirical equations for calculating the effective dynamic viscosity and thermal conductivity of nanofluids are presented based on a high number of experimental data available in the literature. These two equations present the effective dynamic viscosity and thermal conductivity of nanofluids as a function of the volume fraction (0 ≤ ϕ ≤ 12%), size (10nm ≤ dp ≤ 5μm) and type (Ag, Cu, Al2O3, TiO2, CuO, SiO2, ZnO, MgO, Fe, Fe3O4, Al, AlN, CaCO3) of the nanoparticles, temperature and thermo-physical properties of the base fluid. The proposed models are compared with frequent used models in literature (Brinkman and Maxwell-Garnett models) and found that these classical models severely underestimate the effective viscosity and thermal conductivity of nanofluids. Two proposed models are also compared with some other theoretical models, as those of Chon, Patel, Corcione, Prasher, Koo, Maiga, Masoumi, etc. The results showed that, present models for spherical nanoparticle are in excellent agreement with experimental data and provide more accurate character predictions for thermos-physical properties of nanofluid in comparison with existing models. In addition, five new equations are also proposed using the least squares method for calculating the viscosity of five common working fluids (Water, Glycerol, Ethylene glycol (EG), Propylene glycol (PG) and Ethanol) as a function of the temperature. Beside the pure comparison between these models, two well-known benchmark cases of conjugate natural (Differentially Heated Cavity) and mixed convection (Two-sided Lid-driven Cavity) of nanofluid are chosen in order to investigate the effects of the volume fraction, size and type of the nanoparticles on the fluid flow and heat transfer performance of nanofluids. Easy to use for numerical simulation purposes, covering a wide range of the solid particle size and having high accuracy in predicting thermos-physical properties of nanofluids make these equations useful and practical for the design of various thermal engineering systems such as heat exchangers.

Dynamic chiral magnetic effect and anisotropic natural optical activity of tilted Weyl semimetals

We study the dynamic chiral magnetic conductivity (DCMC) and natural optical activity in an inversion-broken tilted Weyl semimetal (WSM). Starting from the Kubo formula, we derive the analytical expressions for the DCMC for two different directions of the incident electromagnetic wave. We show that the angle of rotation of the plane of polarization of the transmitted wave exhibits remarkable anisotropy and is larger along the tilt direction. This striking anisotropy of DCMC results in anisotropic optical activity and rotary power, which can be experimentally observed as a topological magneto-electric effect of inversion-broken tilted WSMs. Finally, using the low energy Hamiltonian, we show that the DCMC follows the universal frac{{bf{1}}}{{{boldsymbol{omega }}}^{{bf{2}}}} decay in the high frequency regime. In the low frequency regime, however, the DCMC shows sharp peaks at the tilt dependent effective chemical potentials of the left-handed and right-handed Weyl points. This can serve as a signature to distinguish between the type-I and type-II Weyl semimetals.

Effects of calcium oxide on the surface properties of industrial sludge by analyzing rheological and electrical properties

Rheological properties in the dynamic regime and complex conductivity measurements were performed on the wastewater sample containing different calcium oxide content. The complex viscosity (η*), the elastic (G’) and loss moduli (G’’) exhibited a linear behavior as a function of angular frequency. These rheological properties were well described by a power-law. Therefore; The values of G’0, G’’0 and η0 corresponding to angular frequency (ω = 1 rad/s) were extracted. Their evolution as a function of calcium oxide content showed that there is a critical amount of calcium oxide content (3 %), from which these parameters showed a net transition indicating the existence of two regions. Similar behavior has been observed from the analysis of the complex conductivity. The hopping conductivity, the ionic strength and the associated relaxation time showed also a net transition at (3 %). A conductivity relaxation behavior was observed in the high frequency and a more detailed analysis of such behavior is reported. This behavior was attributed to the localized relaxation process due to the short-range hopping motion of ions trapped inside the aggregations. The evolutions of the rheological and the electrical properties were analyzed by an equation including two power laws. This equation was able to fit very well their evolution as well to predict the optimal amount of calcium oxide (3 %) needed to achieve the coagulation process.

A comprehensive study of the thermophysical properties of reline and hydrated reline

In this work, a physicochemical characterization of the Deep Eutectic Solvent, reline (formed by chloline chloride and urea in a molar ratio 1:2) and one of its aqueous mixtures (xreline = 0.645) has been made at atmospheric pressure (0.1 MPa) in a wide range of temperatures (288.15–338.15) K for reline and (278.15–338.15) K for the aqueous mixture. The measured properties were: density, speed of sound, refractive index, isobaric molar heat capacity, surface tension, kinematic and dynamic viscosity and electrical conductivity. Additionally, from these experimental results, some derivate properties such as isobaric thermal expansibility, isentropic compressibility, molar refraction, free volume and entropy and enthalpy of surface formation have been obtained. Taking into account the observed behaviour the introduction of water, at the considered composition, only modify drastically the dynamic viscosity and electrical conductivity.

Force Fields with Fixed Bond Lengths and with Flexible Bond Lengths: Comparing Static and Dynamic Fluid Properties

This study investigates the equivalence or differences between classical force fields with rigid bond lengths and the same models but with (harmonic) bond length potentials. For ethane, propane, and dimethyl ether described with the Transferable Anisotropic Mie potential, we vary the force constant of the harmonic bond length potentials and analyze static and dynamic physical properties, namely pressure, viscosity, self-diffusion, and thermal conductivity of homogeneous phases. We find a range of values for the force constant of the bond length potentials (expressed in terms of the period-length of bond-oscillations) where force fields with harmonic bond lengths give equivalent results as the model with rigid bond lengths for static properties, for viscosity, and for self-diffusion coefficients. The thermal conductivity of the force field with rigid bond lengths has an offset compared to the harmonic bond length models, which can be approximated through an analytic correction term. After adding the correction term, results of the rigid model and the flexible models are in rather close agreement. Our study varies time-steps for solving the equations of motion and investigates whether the rRESPA integrator with a small time step associated to the (rather high frequency) bond length potentials has advantages compared to a simple velocity Verlet integrator. Furthermore, this work proposes a fast and memory-efficient prescription to calculate autocorrelation functions for the calculation of Green–Kubo integrals. We then estimate average values and meaningful error bars for dynamic physical properties based on the time-decomposition approach Zhang, Y.; Otani, A.; Maginn, E.J.: Reliable Viscosity Calculation from Equilibrium Molecular Dynamics Simulations: A Time Decomposition Method, J. Chem. Theory Comput. 2015, 11, 3537–3546.

Spin transport properties of anisotropic Heisenberg antiferromagnet on honeycomb lattice in the presence of magnetic field

We have addressed the spin conductivity of a two-dimensional anisotropic antiferromagnet on honeycomb lattice in the presence of a longitudinal magnetic field. A spatial anisotropy in the form of a weak Dzyaloshinskii-Moriya interaction is considered in the model Hamiltonian. Next nearest neighbor exchange coupling has been added to the model Hamiltonian. We have investigated both dynamical and static spin conductivities in terms of the excitation spectrum by means of a hard core bosonic representation. The effects of next-nearest-neighbor coupling and the Dzyaloshinskii-Moriya interaction on the spin transport properties have also been studied via the bosonic model by a Green’s function approach. We have found the temperature dependence of static spin conductivity in the field induced gapped spin-polarized phase for various magnetic field and anisotropy parameters. Furthermore we have studied the magnetic field dependence of the static spin conductivity for various Dzyaloshinskii-Moriya interaction strength and the frequency dependence of the dynamical spin conductivity for various next nearest neighbor coupling constants. We find that the peak in the static spin conductivity moves to higher temperature upon increasing the magnetic field at fixed anisotropy parameter. The static spin conductivity is found to be monotonically decreasing with magnetic field due to increase of the energy gap in the excitation spectrum. Furthermore we have studied the temperature dependence of the spin conductivity for different magnetic field and various next nearest neighbor coupling constants.

Appraising conjugate heat transfer, heatlines visualization and entropy generation of Ag-MgO/H2O hybrid nanofluid in a partitioned medium

Purpose This paper aims to perform the lattice Boltzmann simulation of conjugate natural convection heat transfer, heat flow visualization via heatlines approach and entropy generation in a partitioned medium filled with Ag-MgO (15-85%)/water. Design/methodology/approach The lattice Boltzmann method (LBM) is used to predict the dynamic and thermal behaviors. Experimental correlations for dynamic viscosity and thermal conductivity versus solid volume fraction are used. The study is conducted for the ranges of Rayleigh number 103 ≤ Ra ≤ 106, the partitioner thickness 0.01 ≤ δ ≤ 0.9, its position 0.15 ≤ Xs ≤ 0.85 and the hybrid nano-suspensions volume fraction 0% ≤ ϕ ≤ 2%. Findings The effects of varying of controlling parameters on the convective flow patterns, temperature contours, heat transfers, the heatlines and the entropy generation are presented. It has been found that the maximum rate of heat transfer enhancement occurs for low Ra numbers (103) and is close to 13.52%. The solid thickness d and its horizontal position Xs have a substantial influence on the heat transfer rate, flow structure, heatline, total entropy generation and Bejan number. Besides, the maximum heat transfer is detected for high Ra and δ ≈ 1 and the percentage of augmentation is equal to 65.55% for ϕ = 2%. According to the horizontal position, the heat transfer remains invariant for Ra = 103 and takes a maximum value near the active walls for Ra ≥ 104. The total entropy generation increases with Ra and decreases with ϕ for Ra = 106. The increase of ϕ from 0 to 2% leads to a reduction in close to 40.76%. For this value of Ra, the entropy is the maximum for δ = 0.4 and Xs = 0.35 and Xs = 0.65%. Moreover, as the Ra increases the Bejan number undergoes a decrease. The Bejan number is the maximum for Ra = 103 independently to δ and Xs. The superior thermal performance manifests at low Ra and high value of δ independently to the positions of the conducting body. Originality/value The originality of this paper is to analyze the hybrid nano-additive effects on the two-dimensional conjugate natural convection in a partitioned medium using the LBM. The experimental correlations used for the effective thermal conductivity and dynamic viscosity give credibility to our study. Different approaches such as heatlines and entropy generation are used.

Enhancement of thermo-mechanical stability for nanocomposites containing plasma treated carbon nanotubes with an experimental study and molecular dynamics simulations

This study investigated differences in the thermo-mechanical properties of thermosetting polymer EPON 826 nanocomposites reinforced by modified nanofillers. Carbon nanotubes (CNTs) were modified by environmentally friendly plasma treatments. Composites containing various nitrogen doped CNTs were investigated by morphological and structural analysis, which confirmed that they provided better dispersion and stronger interfacial interaction with the epoxy matrix. In addition, the dynamic mechanical behavior and thermal conductivity were analyzed to understand the energy transfer mechanism in the nanocomposites. The thermal and mechanical properties of the Inductively coupled plasma treated CNTs (ICP-CNT) reinforced nanocomposites containing a high concentration of quaternary and pyridinic types were higher than that of mechanical shear force plasma treated CNTs (MSF-CNT). A molecular dynamics (MD) simulation was performed to support the experimental results and confirmed that controlling the type of nitrogen doping groups was important for improving the thermo-mechanical characteristics of CNT/epoxy nanocomposites.

Effects of Functionalized Nano-TiO2 on the Molecular Motion in Epoxy Resin-Based Nanocomposites.

Epoxy resin-based nanocomposites have been widely researched for being potential insulating materials in high voltage power equipment. In this paper, nano-TiO2 particles were chosen and surface-modified by a silane coupling agent containing an epoxy group. The effect of functionalized nano-TiO2 doping on the physical properties of epoxy resin was studied. The results of differential scanning calorimetry show that Tg increased significantly and can be increased by up to 35 °C. Therefore, it is believed that the suppression of molecular motion by the addition of nanofillers works effectively in the case of this functionalized nano-TiO2 and a strong interaction between the epoxy resin and the nano-TiO2 was formed after surface modification. Consequently, dynamic mechanical properties, thermal conductivity, electrical conductivity, and trap characteristics of epoxy resin are all adjusted after introducing functionalized nano-TiO2. All of these physical properties were analyzed from the perspective of suppression of molecular motion, and it is of significance to establish the theory of a nanocomposite dielectric. Besides, the results show that the epoxy/TiO2 nanocomposite is expected to be applied in the insulation system of electrical equipment.

Graphene nanofl akes and hybrid nanocomposites with gold and silver nanoparticles: optical and thermal properties

New technologies for the preparation of graphene nanofl akes (GNF) with noble metal nanoparticles (NPs), specifi cally Au and Ag, as well as hybrid nanocomposites composed of metal microspheres coated with nanostructures [GNF+metal NPs], were considered. The optical properties of metal nanoparticles, their adsorption characteristics with respect to graphene fl akes, and the thermophysical properties of the obtained functional nanomaterials were studied. The obtained data on dynamic optical absorption and thermal conductivity makes it possible to propose new fi elds of application of graphene materials.

Terahertz Electrodynamics in Transition Metal Oxides

AbstractTransition metal oxides (TMOs) are among the most contemporary topics in condensed matter research. For over the past three decades, the most astounding discoveries of high temperature superconductivity, colossal magnetoresistance, multiferroics, topological matter, and several other novel electronic and magnetic phases have been realized and hosted in the TMOs. Almost simultaneously and specifically during the past 5 years, the implementation of terahertz (THz) spectroscopy to unveil the complexity of such materials has delivered unprecedented success. THz spectroscopy extracts material parameters such as dynamic conductivity, dielectric constant, and magnetic permeability in spectral range of 1–20 meV. This imparts the capability to probe a variety of quasiparticles emerging from the electrodynamics of collective, bound and free charge carriers, and complex spin orders, which is the key to decode the complex phases of TMOs class of quantum matter. Herein, the THz spectroscopic investigations of quasiparticle electrodynamics of correlated TMOs are reviewed. Several long‐standing issues are resolved and there is enormous potential for a lot more to offer, emphasizing the growing indispensability of THz technology in condensed matter.

Dynamical conductivity in the multiply degenerate point-nodal semimetal CoSi

We investigate the dynamical conductivity in multiply-degenerate point-nodal semimetal CoSi. In the semimetal, the band structure holds point nodes at the $\Gamma$ and R points in the Brillouin zone and more than three bands touch at the nodes. Around the nodes, electronic states are predicted to be described as the multifold chiral fermion, a new class of fermion. We show that the dynamical conductivity exhibits a characteristic spectrum corresponding to the band structure and the chiral fermionic states. The dynamical conductivity of CoSi is calculated as a function of photon energy by using the first-principles band calculation and linear response theory. We show that a dip structure in the low photon-energy region is attributed to not only the band structure but also the chirality of electronic states. The chirality leads to the prohibition of transition between the lower and upper bands of threefold chiral fermion and thus the transition between the middle and lower bands is relevant to the dynamical conductivity. This transition property is different from the Dirac and Weyl semimetals, the other point-nodal semimetals, where the excitation between the upper and lower bands is relevant to the dynamical conductivity. We discuss the relation between the prohibition and the dip structure by using an effective Hamiltonian describing threefold chiral fermion.

Quantum coherence and the localization transition

A dynamical signature of localization in quantum systems is the absence of transport which is governed by the amount of coherence that configuration space states possess with respect to the Hamiltonian eigenbasis. To make this observation precise, we study the localization transition via quantum coherence measures arising from the resource theory of coherence. We show that the escape probability, which is known to show distinct behavior in the ergodic and localized phases, arises naturally as the average of a coherence measure. Moreover, using the theory of majorization, we argue that broad families of coherence measures can detect the uniformity of the transition matrix (between the Hamiltonian and configuration bases) and hence act as probes to localization. We provide supporting numerical evidence for Anderson and Many-Body Localization (MBL). For infinitesimal perturbations of the Hamiltonian, the differential coherence defines an associated Riemannian metric. We show that the latter is exactly given by the dynamical conductivity, a quantity of experimental relevance which is known to have a distinctively different behavior in the ergodic and in the many-body localized phases. Our results suggest that the quantum information-theoretic notion of coherence and its associated geometrical structures can provide useful insights into the elusive nature of the ergodic-MBL transition.

On evaluation of thermophysical properties of transformer oil-based nanofluids: A comprehensive modeling and experimental study

Transformer oil-based nanofluids are known to have higher thermal conductivity and heat transfer performance compared to conventional transformer oils. In this study, four different types of transformer oil-based nanofluids are synthesized using the well-known two-step method. The first nanofluid contains pure multi-walled carbon nanotubes (MWCNTs), while other samples consist of 20 Vol% of MWCNTs and 80 Vol% of different oxide nanoparticles (i.e., Al2O3, TiO2, and SiO2). The dynamic viscosity and thermal conductivity of prepared samples are investigated in seven different volume fractions of 0.001, 0.0025, 0.005, 0.01, 0.025, 0.05, and 0.1%. Besides, the breakdown voltage of the pure transformer oil and nanofluids containing 0.05 and 0.1 Vol% of nanoparticles is investigated. The outcomes show that dielectric properties of hybrid carbon-based nanofluids are far better compared to those properties of the pure MWCNTs nanofluids. Finally, eight different soft computing approaches, including group method of data handling (GMDH), support vector machine (SVM), radial basis function (RBF) neural network, multilayer perceptron (MLP), and MLP and RBF models optimized with bat and grasshopper optimization algorithm (GOA), are used to model the viscosity and thermal conductivity of synthesized nanofluids. The outcomes show that the GMDH approach significantly outperforms all other models in terms of predicting the thermal conductivity and dynamic viscosity of transformer oil-based nanofluids.

Ab initio simulations for expanded gold fluid in metal-nonmetal transition regime

Ab initio simulations based on quantum molecular dynamics have been performed to study the electrical and optical properties of expanded gold fluids from one to a sixth of the normal solid density and with temperatures varying from 5000 to 20 000 K. With decreasing density, the dynamic conductivity evolves from the characteristic of a metal to that of a nonmetal. The DC conductivity is given by fitting the dynamic conductivity using the Drude or Drude-Smith model. According to the shift of the central peak of dynamic conductivity, the change of the slope of DC conductivity with respect to temperature, and the appearance of the disconnected network in the charge density distribution, the metal-nonmetal transition of expanded gold fluids occurs in the vicinity of one-third of the normal solid density. In addition, as the density decreases, the localization of 6s and 5d states is observed in the density of states.