Temperature Relaxation Time Research Articles

Intelligent Predictive Networks for Cattaneo-Christov Heat and Mass Transfer Dissipated Williamson Fluid Through Double Stratification

This study aims to develop an efficient predictive model for Cattaneo-Christov heat and mass transformation of dissipative Williamson fluid with the effects of double stratification (CCHMT-DWF-DS) using the Levenberg-Marquardt Backpropagation (LMA-BP) algorithm. The under-consideration Williamson fluid flow is magneto-hydro-dynamic, incompressible and two-dimensional through a stretching sheet. The mathematical model of nonlinear partial differential equations for physical phenomena is transformed into ordinary differential equations by means of renowned similarity transformations. The solutions of physical problem are computed by bvp4c technique through MATLAB. The LMA-BP is employed to train a backward neural network capable of accurately predicting velocity, temperature, and concentration profiles under various physical conditions such as changes in the Hartmann number , Prandtl number , Schmidt number , Williamson parameter , the relaxation time of temperature , the relaxation time of concentration , temperature stratification , and concentration stratification for generating a variety of graphical outcomes and statistics. This research is significant for its innovative use of the LMA-BP in analyzing the complex dynamics of non-Newtonian fluids specifically the Williamson fluid, alongside the Cattaneo-Christov heat and mass flux model. The obtaining graphs have been discussed in detail. The thermal and solutal relaxation factors reduce heat and mass flow while fluid motion is delayed by the time-dependent parameter and further reduced by the Hartman number. The Cattaneo-Christov heat flux model enhances simulation accuracy by integrating temporal delays in heat transfer, proving beneficial for sophisticated industrial and scientific endeavors related to non-Newtonian fluids. This analysis offers a powerful predictive tool for applications in thermal management, industrial cooling systems, and biomedical fluid dynamics, advancing machine learning in fluid mechanics.

Physics-informed neural networks approach for pollutant dispersion flow caused by magnetic dipole

Abstract Research on the liquid flow and distribution of waste discharge concentration over cylindrical surfaces might lead to the growth of efficient waste management and pollution controlling strategies. In view of this, the pollutant concentration and magnetic dipole impact on the liquid flow through the cylinder with a porous medium are explored in the present analysis. Moreover, Fourier’s and Fick’s laws are considered to explore heat transport features. The governing partial differential equations (PDEs) of the present study are converted into non-dimensional ordinary differential equations (ODEs) utilizing similarity variables. Also, the current study proposes a novel implementation of neural networks based on physics knowledge for the liquid flow past a cylinder. The self-updating weights and bias facilitate the network to satisfy the minimization objective function and provide accurate results. Additionally, the solution obtained by Runge Kutta Fehlberg's fourth-fifth order (RKF-45) method is utilized to validate the physics-informed neural network (PINN) results, presenting mean squared errors from 10-9 to 10-11. Furthermore, it is found that the increase in temperature relaxation time parameter decreases the Nusselt number gradually at the rate of 1 to 5%. An upsurge in the values of the pollutant external source parameter and the pollutant external source variation parameter decreases the concentration profile.

Dynamics of Fourier's and Fick's laws on the convectively heated oscillatory sheet under Arrhenius kinetics: The finite-difference technique

The significance of chemical reaction with activation energy and convective boundary conditions on the fluid flow via an oscillatory stretchy surface in the presence of permeable media and radiation is analyzed in this study. This inspection presents Fourier and Fick's laws-based equations for heat, mass transport, and liquid flow through an oscillating stretchy sheet. Understanding these dynamics aids in the optimisation of catalytic reaction settings, where gradients greatly influence reaction rates in concentration and temperature. The governing differential equations of the current study are modelled and changed into their non-dimensional form by employing suitable similarity variables. The finite difference method (FDM) is also used to numerically solve the obtained dimensionless equations. The influence of many factors on the several profiles is portrayed with graphical representations. The outcome of the unsteadiness and porosity parameters on the velocity profile with time coordinate is depicted. The increase in the radiation parameter and Biot number upsurges the thermal profile. The temperature reduces as the unsteadiness parameter and temperature relaxation time parameter grow. The upsurge in the activation energy parameter intensifies the mass transport. The rise in concentration relaxation time parameter diminishes the concentration profile.

Thermal Relaxation in Janus Transition Metal Dichalcogenide Bilayers.

In this work, we employ molecular dynamics simulations with semi-empirical interatomic potentials to explore heat dissipation in Janus transition metal dichalcogenides (JTMDs). The middle atomic layer is composed of either molybdenum (Mo) or tungsten (W) atoms, and the top and bottom atomic layers consist of sulfur (S) and selenium (Se) atoms, respectively. Various nanomaterials have been investigated, including both pristine JTMDs and nanostructures incorporating inner triangular regions with a composition distinct from the outer bulk material. At the beginning of our simulations, a temperature gradient across the system is imposed by heating the central region to a high temperature while the surrounding area remains at room temperature. Once a steady state is reached, characterized by a constant energy flux, the temperature control in the central region is switched off. The heat attenuation is investigated by monitoring the characteristic relaxation time (τav) of the local temperature at the central region toward thermal equilibrium. We find that SMoSe JTMDs exhibit thermal attenuation similar to conventional TMDs (τav~10-15 ps). On the contrary, SWSe JTMDs feature relaxation times up to two times as high (τav~14-28 ps). Forming triangular lateral heterostructures in their surfaces leads to a significant slowdown in heat attenuation by up to about an order of magnitude (τav~100 ps).

Механический тепловой ключ криогенного магнитного рефрижератора

This work study the operating parameters of a cryogenic mechanical thermal switch, a detachable contact pair made of a alloy GdNi2 disk and a copper cylinder. The mechanical thermal switch operates in a vacuum in the temperature range of 8-325 K with a pressure of 250-350 kPa. The time of thermal equilibrium is studied at different contact areas with and without an indium thermal interface at an initial temperature difference of 0.8-10 K in the contact pair in the temperature range from 8 to 122 K. The temperature relaxation value is 33.7...39.9 seconds at a temperature difference of 3±0.14 K in the range of 50...122 K. Reducing the nominal contact area from 177 mm2 to 2.5 mm2 increases the temperature relaxation time at a temperature of 73.3 K from 36.6 to 63.5 seconds. This temperature range corresponds to the maximum magnetocaloric effect near the Curie temperature of the GdNi2 alloy. The values of the heat that must be removed to maintain the required temperature of the cooling object in a cryogenic magnetic refrigerator have been obtained.

The distributed order models to characterize the flow and heat transfer of viscoelastic fluid between coaxial cylinders

The distributed order fractional derivatives can describe complex dynamic systems. In this paper, considering the periodic pressure gradient and magnetic field, the time distributed order fractional governing equations are established to simulate the two-dimensional flow and heat transfer of viscoelastic fluid between coaxial cylinders. Numerical solutions are obtained by the L1 approximation for the Caputo derivative (L1-scheme) and the finite difference method, and the effectiveness of numerical method is verified by a numerical example. Results demonstrate that the time distributed fractional Maxwell model can promote the flow while the distributed Cattaneo model can weaken heat transfer than the fractional Maxwell and Cattaneo model, and different weight coefficients have different effects on the fluid. The effect of physical parameters, such as the relaxation time of velocity and temperature λ 1, λ 2, the magnetic parameter M, the amplitude P 0 and frequency w of pressure gradient, and the Prandtl number Pr on velocity and temperature are discussed and analysed in detail.

Interplay between dynamic heterogeneity and interfacial gradients in a model polymer film.

Glass-forming liquids exhibit long-lived, spatially correlated dynamical heterogeneity, in which some nm-scale regions in the fluid relax more slowly than others. In the nanoscale vicinity of an interface, glass-formers also exhibit the emergence of massive interfacial gradients in glass transition temperature Tg and relaxation time τ. Both of these forms of heterogeneity have a major impact on material properties. Nevertheless, their interplay has remained poorly understood. Here, we employ molecular dynamics simulations of polymer thin films in the isoconfigurational ensemble in order to probe how bulk dynamic heterogeneity alters and is altered by the large gradient in dynamics at the surface of a glass-forming liquid. Results indicate that the τ spectrum at the surface is broader than in the bulk despite being shifted to shorter times, and yet it is less spatially correlated. This is distinct from the bulk, where the τ distribution becomes broader and more spatially organized as the mean τ increases. We also find that surface gradients in slow dynamics extend further into the film than those in fast dynamics-a result with implications for how distinct properties are perturbed near an interface. None of these features track locally with changes in the heterogeneity of caging scale, emphasizing the local disconnect between these quantities near interfaces. These results are at odds with conceptions of the surface as reflecting simply a higher "rheological temperature" than the bulk, instead pointing to a complex interplay between bulk dynamic heterogeneity and spatially organized dynamical gradients at interfaces in glass-forming liquids.

Amendments of weld formation in human skin laser soldering.

A computational modeling is employed for quantitative assessment of weld formation and area of tissue temperature necrosis during the human skin laser soldering. The evaluation is carried out depending on the components composition of using solders, including bovine serum albumin (BSA), indocyanine green (ICG), and carbon nanotubes (CNT), as well as the angle of incidence of laser light and its pulse duration. The influence of CNT on the change of thermodynamic characteristics of albumin denaturation and the rate of formation of the laser weld is investigated. The obtained results suggest to limit the duration of laser light pulse by temperature relaxation time to minimize transfer of thermal energy to reduce the heating of human skin tissues. The developed model has a great potential for further optimization of laser soldering of biological tissues technology with greater efficiency in minimizing the weld area. This article is protected by copyright. All rights reserved.

Magnetic diffusion of time distributed-order Maxwell fluid in boundary layer under the action of induced magnetic field

Hydrogel has been widely used in energy storage devices and flexible electronic equipment. To promote its applications, a laminar boundary layer model is proposed to analyze the velocity and temperature distributions in the mold. Based on the time distributed-order Maxwell and Cattaneo constitutive relations, the research establishes governing equations of unsteady two-dimensional incompressible viscoelastic electrically conducting hydrogel taking into account the induced magnetic field. When the magnetic Reynolds number is large enough, it is necessary to consider the magnetic diffusion in the boundary layer. The effects of thermal radiation and velocity slip are also considered at the same time. The Gauss quadrature rule is used to approximate the distributed-order integral, and then the numerical solution of the model is obtained by using the finite difference method and the L1-algorithm. The analytical solution is constructed to verify the effectiveness of the numerical solution. The results show that the fluid velocity decreases with the increment of magnetic parameter, while the induced magnetic field increases. The boundary layer thickness of velocity, induced magnetic field, and thermal becomes thinner with the enlargement of velocity and temperature relaxation time parameters. Moreover, the distributed-order and the fractional constitutive models are compared through different weight coefficients, and it is found that the fractional constitutive model obtains larger velocity and temperature distributions.

Generalized thermoelastic dissipation in micro/nano-beams with two-dimensional heat conduction

The precise prediction of quality factor based on thermoelastic dissipation (TED) is of great importance for the optimal design of micro/nano-resonators. In this work, employing the nonlocal-dual-phase-lag (NDPL) model and the modified-couple-stress (MCS) model, analytical TED expressions are developed for the first time for micro/nano-beam resonators with two-dimensional (2D) heat conduction along the thickness and length directions. Initially, the governing equation of NDPL coupled thermoelasticity is established, and then the solutions of 2D fluctuation temperature are obtained by utilizing the Galerkin approach. Subsequently, the natural frequency involving the MCS size-dependence length-scale parameter is achieved based on the governing equation of vibration. Finally, analytical generalized TED models are attained according to the energy-definition approach. Three representative types of constraint boundary conditions for the beam resonator, namely, clamped-clamped, clamped-free, and simply supported, are considered in this study. And the present developed TED models are confirmed to possess perfect generality and excellent convergence performance. Moreover, an expression of equivalent thermal relaxation time in the 2D case is introduced and expressed in terms of the length- and thickness-directional thermal relaxation times. Two typical materials, silicon and gold, are selected in the simulation part. The exploration of fluctuation temperature, TED spectra, and thermal relaxation times considering multiple physical effects is conducted as an emphasis. Results reveal that the effect of heat-conduction dimension is crucial for micro/nano-beams with a small ratio of length to thickness, while the significant NDPL effect is dependent upon the ultra-high vibration frequency. Additionally, the MCS size-dependence effect can enhance the natural frequency and improve the quality factor of micro/nano-beam resonators.

SOLAR ENERGY ENCOURAGEMENT IN SOLAR HVAC USING EYRING-POWELL TERNARY-HYBRID NANOFLUID FLOW IN POROUS MEDIUM WITH CATTANEO-CHRISTOV HEAT AND MASS FLUXES

This study presents a new 3D mathematical model to analyze rotating Eyring-Powell ternary-hybrid nanofluid flow in solar HVAC systems. The study examines the flow of a mixture of tri-hybrid nanoparticles inserted into ethyl glycol over a stretching sheet through a porous medium. The model considers solar thermal radiation, activation energy impact, and boundary qualifications. Similarity variables are used to transform governing equations into a set of nonlinear coupled ordinary differential equations, which are solved numerically using the Runge-Kutta-Fehlberg approach in MAPLE 2022 software. The results are shown graphically to investigate the impacts of regulating parameters on skin friction, heat, and mass transfer. It is demonstrated that an increase in the Eyring-Powell fluid and rotation parameters increases radial skin friction. Furthermore, the temperature slip and relaxation time parameters tend to reduce the Nusselt number, while the radiation parameter boosts the Nusselt number. The use of ternary nanofluids results in the highest Nusselt numbers. The study has importance in engineering applications such as the dying of metals and extrusion processing.

Shear viscosity of hadronic matter at finite temperature and magnetic field

We calculate the transport coefficient of hadronic matter in the presence of temperature and magnetic field using the linear sigma model. In the relaxation time approximation, we estimate the shear viscosity over entropy density $\eta/s$. The point-like interaction rates of hadrons are evaluated through the $S$-matrix approach in the presence of a magnetic field to obtain the temperature and magnetic field-dependent relaxation time. We observe that the transport coefficients are anisotropic in the presence of the magnetic field. We calculate the temperature and magnetic field-dependent anisotropic shear viscosity coefficients by incorporating the estimated relaxation time. The value of viscosity over entropy density is lower in the presence of a magnetic field than the value of it in a thermal medium. The behavior of the perpendicular components of the shear-viscous coefficient is also discussed. We consider the temperature-dependent hadron masses from mean-field effects in this work.

Bitumen-polymer compositions for asphalt concrete

AnnotationOne of the criteria for the level of development of countries is the condition of the road network. At present, the transport and operational characteristics of the majority of domestic highways lag behind the world level. Therefore, the need to create road surfaces with increased durability is very urgent. As a result of this research bitumen modified with polymers have been investigated. Based on measurements of time-dependent viscosity parameters (melting temperature, penetration and spin-spin relaxation time T2), it was found that at a thiol content of more than 25%, a continuous phase can form, which manifests itself as a sharp change in the properties of bitumen and is associated with phase inversion. A good compatibility of thermoplastic elastomers with a bituminous binder was revealed, and the resulting modified systems have high technical characteristics The proposed method for modifying bitumen can be recommended for obtaining roofing materials.

Kinetic model for electron-ion transport in warm dense matter.

We present a model for electron-ion transport in warm dense matter that incorporates Coulomb coupling effects into the quantum Boltzmann equation of Uehling and Uhlenbeck through the use of a statistical potential of mean force. Although the model presented here can be derived rigorously in the classical limit [S. D. Baalrud and J. Daligault, Phys. Plasmas 26, 082106 (2019)PHPAEN1070-664X10.1063/1.5095655], its quantum generalization is complicated by the uncertainty principle. Here we apply an existing model for the potential of mean force based on the quantum Ornstein-Zernike equation coupled with an average-atom model [C. E. Starrett, High Energy Density Phys. 25, 8 (2017)1574-181810.1016/j.hedp.2017.09.003]. This potential contains correlations due to both Coulomb coupling and exchange, and the collision kernel of the kinetic theory enforces Pauli blocking while allowing for electron diffraction and large-angle collisions. We use the Uehling-Uhlenbeck equation to predict the momentum and temperature relaxation times and electrical conductivity of solid density aluminum plasma based on electron-ion collisions. We present results for density and temperature conditions that span the transition from classical weakly-coupled plasma to degenerate moderately-coupled plasma. Our findings agree well with recent quantum molecular dynamics simulations.

Periodic stick–slip mode of ice surface premelting during friction

The rheological nonlinear model of ice surface softening during friction is developed. Analytical and numerical schemes describing stick–slip frictional oscillations for three boundary relations between the shear strain, stress, and temperature relaxation times are built. The phase portraits and time dependencies of friction force are calculated. The random force (additive uncorrelated noise) effect on found damped oscillation mode is revealed. It is shown that white noise influence leads to an undamped oscillation mode corresponding to a periodic intermittent (stick–slip) regime of friction that is basically responsible for destruction of rubbing surfaces. The most pronounced such oscillatory behavior occurs if relaxation time of the temperature is much longer that its value for shear strain and stress.

High-Temperature Magic-Angle Spin Nuclear Magnetic Resonance Reveals Sodium Ion-Doped Crystal-Phase Formation in FLiNaK Eutectic Salt Solidification

The new salt heating magic-angle spin (MAS) system for high-temperature nuclear magnetic resonance (HT-NMR) is achieved by a laser heating beam coupled with optical fiber. The formation of a sodium ion-doped crystal KF phase is revealed in FLiNaK ternary eutectic salt (46.5%LiF–11.5%NaF–42.0%KF), which is considered unable to exist at room temperature according to its phase diagram. Density functional theory (DFT) simulation proved that Na+ ion-doped crystal is clearly ascertained to develop with the solidification of the melt. Temperature dependence, relaxation, and variable contact time cross-polarization NMR studies provide insights into the unique dynamics and the spatial scale of the doped Na+ ions in KF crystals, which exhibit faster ionic vibration due to the weakening of coordinated interactions from the ambient F– ions.

Optical absorption window in Na3Bi based three-dimensional Dirac electronic system

We present a detailed theoretical study of the optoelectronic properties of a Na3Bi based three-dimensional Dirac electronic system (3DDES). The optical conductivity is evaluated using the energy-balance equation derived from a Boltzmann equation, where the electron Hamiltonian is taken from a simplified k⋅p approach. We find that for short-wavelength irradiation, the optical absorption in Na3Bi is mainly due to inter-band electronic transitions. In contrast to the universal optical conductance observed for graphene, the optical conductivity for Na3Bi based 3DDES depends on the radiation frequency but not on temperature, carrier density, and electronic relaxation time. In the radiation wavelength regime of about 5μm<λ<200 μm, an optical absorption window is found. This is similar to what is observed in graphene. The position and width of the absorption window depend on the direction of the light polarization and sensitively on temperature, carrier density, and electronic relaxation time. Particularly, we demonstrate that the inter-band optical absorption channel can be switched on and off by applying the gate voltage. This implies that similar to graphene, Na3Bi based 3DDES can also be applied in infrared electro-optical modulators. Our theoretical findings are helpful in gaining an in-depth understanding of the basic optoelectronic properties of recently discovered 3DDESs.

Fluence and wavelength dependent ultrafast differential transmission dynamics in graphene

We performed degenerate pump-probe transmission measurements of graphene supported on glass for a range of pump fluences that enable us to observe both positive and negative deferential transmission dynamics. Our results show that at an intermediate pump fluence, where a transition from negative to positive response occurs, the differential transmission dynamics is an order of magnitude faster than at higher and lower pump fluences. This effect can be explained by equal contributions of inter- and intraband transitions with opposite signs to the transient optical conductivity of graphene at an intermediate pump fluence. Moreover, the intermediate threshold pump fluence is shown to increase with decreasing probe energy, which is in agreement with the theoretical model. Furthermore, we show that the relaxation time of the electronic temperature increases monotonically over the range of fluences studied. In perspective, this work is of importance to graphene-based opto-electronic applications such as light modulators.

Dynamic relaxations of a metallic glass studied on cooling

Metallic glasses have many intrinsic and universal dynamic relaxations observed below the glass-transition temperature. However, these relaxations have mostly been studied on heating and seldom investigated on cooling. In the present work, the slow β and fast β′ relaxations of La60Ni15Al25 metallic glass are studied in sequential heating and cooling experiments under continuous mechanical vibration using a dynamic mechanical analyzer. A slow β relaxation peak is observed on cooling, and compared with the preceding heating step, its peak temperature, activation energy and characteristic relaxation time are all shifted to lower values. On the contrary, a fast β′ relaxation peak is always present on heating, but undetectable on consequent cooling. Only when the metallic glass is cooled below a critical temperature, a certain value of supercooling is achieved, then the fast β′ relaxation is found during subsequent reheating. The work introduces a new approach to investigate dynamic relaxations in metallic glasses and discusses a new possibility of the origin of the fast β’ relaxation.

Numerical Simulations of Shock Waves in Viscous Carbon Dioxide Flows Using Finite Volume Method

An efficient numerical tool for studying shock waves in viscous carbon dioxide flows is proposed. The developed theoretical model is based on the kinetic theory formalism and is free of common limitations such as constant specific heat ratio, approximate analytical expressions for thermodynamic functions and transport coefficients. The thermal conductivity, viscosity and bulk viscosity coefficients are expressed in terms of temperature, collision integrals and internal energy relaxation times. Precomputed in the wide temperature range thermodynamic functions and transport coefficients are implemented to the numerical code which is used for the simulations of the shock wave structure. Including the bulk viscosity to the kinetic model results in the increasing shock width and improves the agreement with experimental data.