Local Non-equilibrium State Research Articles

Natural convection pump having local nonequilibrium states with heaters for microfluidic circuits

A small pump with a simple structure that can be driven at low voltage remains under development in the research stage. In this study, we propose a small natural convection pump that has local nonequilibrium states with heaters for microfluidic circuits, and experimentally examine its pumping performance. In other words, by setting four small units comprising a hot fluid region with a buoyancy force and a cold fluid region in a circular channel, we obtained a maximum pumping velocity of ∼0.6 mm s−1 with an applied voltage of 3 V. Our device is beneficial as microfluidic circuits because the performance of our device is sufficiently practical.

Modeling rarefied gas-solid surface interactions for Couette flow with different wall temperatures using an unsupervised machine learning technique.

In rarefied gas flows, discontinuity phenomena such as velocity slip and temperature jump commonly appear in the gas layer adjacent to a solid boundary. Due to the physical complexity of the interactions at the gas-solid interface, particularly in the case of systems with local nonequilibrium state, boundary models with limited number of parameters cannot completely describe the reflection of gas molecules at the boundary. In this work, the Gaussian mixture (GM) model, which is an unsupervised machine learning technique, is employed to construct a statistical gas-solid surface scattering model based on the collisional data obtained from molecular dynamics (MD) simulations. The GM model is applied to study Couette flow for different inert gases (Ar and He) confined between two parallel infinite gold walls at different temperatures. A direct comparison between the results obtained from the GM model and the Cercignani-Lampis-Lord (CLL) scattering kernel against the MD collisional data in terms of the distribution of the predicted postcollisional velocities, and accommodation coefficients has shown that the results from the GM model are an excellent match with the MD results outperforming the CLL scattering kernel. As an example, for He gas, while the predicted energy accommodation coefficient by the CLL model is more than two times higher than the MD predictions, the value computed by the GM model is in excellent agreement with the MD results. This superior performance of the GM model confirms its high potential to derive a generalized boundary condition in systems encountered with highly nonequilibrium and complex gas flow conditions.

Numerical study of fast transient non-diffusive heat conduction in a porous medium composed of solid-glass spheres and air using fractional Cattaneo subdiffusion model

This research aims to carry out the fast-transient process of heat flow in a porous medium, proposing the Caputo-type fractional Cattaneo subdiffusion model to study the anomalous diffusion process in the temperature response of the two-phase system. It has been shown that during the short thermal disturbance of porous medium, the solid-fluid interactions in microscale, energy swap through the solid-glass spheres and air, the local non-equilibrium state, and also the fast transient process can be simulated by use of fractional calculus approach. The classical Fourier model fails to interpret such effects, because it is assumed that the thermal wave propagates with infinite speed, and also the thermal interactions between phases occur simultaneously. The energy equation has been developed upon the Caputo fractional derivative, then numerically solved and it has been observed that its results are comparable to the measured data, which reveals the accuracy of the time-fractional model proposed. The numerical results exactly follow the experimental data, which illustrates the applicability of fractional Cattaneo subdiffusion model for examining the transient process in a porous medium at the short temporal scales, and also its capability to interpret the solid-fluid interactions in microscale.

Biological systems as nonequilibrium structures described by kinetic methods

Traditionally biological objects are described by means of methods of the macroscopic physics, but the kinetic approach allows us to understand deeper the essence of living systems. A special problem is formulated for the kinetic equation to simulate the basic features of the biological systems related to local nonequilibrium states. The biological system is treated as the dissipative structure which “feeds” the negentropy, and the statistical entropy expressed through the distribution function for the nonequilibrium open system supports this viewpoint. Sizes of a biostructures as the regions of spatially nonuniform nonequilibrium distributions of the open system are estimated. These evaluations are compared with empirical evidence concerning the dependence of the sizes of mammals and green leaves on the intensity of the metabolism.

Photoinduced Local Nonequilibrium States in Superconductors: Hot Spot Model

The so-called hot spot model is often used to study problems concerning the local heating of electrons and phonons and local suppression of superconductivity by electromagnetic radiation. This model implies that the dynamics of a system in a certain time interval can be described by a locally equilibrium electron distribution function, but the electron temperature Te differs from the equilibrium value. Such an assumption makes it possible to use the heat equation to study the temporal and spatial dynamics of Te and significantly simplifies the study of the dynamic response of a superconductor. Examples of the use of this model to describe nonequilibrium effects occurring in systems with different types of superconducting pairing under electromagnetic irradiation have been presented in this work.

T0501-2-4 ナノ構造が固液界面熱抵抗に及ぼす影響に関する分子動力学的研究([T0501-2]マイクロ・ナノスケールの熱流体現象(2))

The nonequilibrium molecular dynamics simulation was conducted in order to clarify the effects of the surface adherent structures in nanometer scale on a thermal resistance at a liquid-solid interface as well as the reduction mechanism. The surface structural clearances and the potential parameter between liquid molecules and solid atoms were changed as the calculation parameters in order to discuss general nanostructural effects on the interfacial thermal resistance. The local nonequilibrium behaviors were observed between the nanostructures depending on the degrees of freedom of the liquid molecules and the diffusion coefficients of liquid molecules at the interface are enhanced by the local nonequilibrium state depending on the surface adherent structures in nanometer scale only in the case of Lennard-Jones potential liquid model.

A nonequilibrium irreversible thermodynamics model for material damping

Material damping in a continuum, which inherently involves multiple coupled irreversible thermodynamic processes, is associated with irreversible interchanges of various forms of energy. In this paper, a hybrid framework of internal state variables and extended state variables is proposed to formulate a material damping model for complex materials. For a typical simple material, damping model is developed in the framework of extended irreversible thermodynamics. Nonequilibrium quantities, i.e. thermodynamic fluxes, are introduced as extended state variables to supplement for the description of a local nonequilibrium state. The relaxation characteristics of these thermodynamic fluxes, which are a symbol of nonequilibrium characteristics, are modeled by first-order relaxation equations. For a typical system, we introduced heat flux and nonequilibrium (viscous) stresses as thermodynamic fluxes corresponding to irreversible heat transport and viscous processes. Coupling between equilibrium and nonequilibrium mechanical and thermal fields are modeled. Explicit expressions for specific free energy, specific entropy, and specific internal energy are derived. The energy balance equation that governs interchanges of various forms of energy is then obtained to complete the formulation. We have investigated various limiting cases of the developed model and related these limiting cases to typical thermodynamic damping models. We have applied the model to study the dissipation characteristics of longitudinal vibrations of a rod and then compared with other damping models.

The joint analysis of general aspects of the phenomenological thermodynamics and the kinetic Boltzmann theory

The question of agreement of the kinetic moment theory with the first principle continuum thermodynamics is considered. The characteristics of distribution function describing local non-equilibrium state of monatomic gases are analyzed. In the first approach on non-equilibrium variables the equations making more exact the results of Chapman and Enskog are received. The paradox of heat conduction is eliminated and the coincidence of theoretical and experimental data on dispersion of sound speed in inert gases is improved.

Universal inaccessibility principle

The universal inaccessibility principle (UIP) which was previously used in developing the generalized phenomenological irreversible thermodynamic theory (GPITT) is discussed at length. UIP provides both the thermodynamic temperature and the corresponding entropy function for a local nonequilibrium state without involving any physical device. The Caratheodory principle is obtained as a particular case of the equilibrium part of UIP. The system with negative temperatures are also covered by UIP. It is revealed that the use of UIP is implied in the De Donderian thermodynamic description of irreversibility due to chemical reactions and also in the classical irreversible thermodynamic description of Onsager-Prigogine-Meixner-de Groot. The reversible adiabatic paths of a chemically reactive closed system remain perfectly isentropic even if concomitantly a chemical conversion takes place within the system.

Unsteady heat conduction by internal-energy waves in solids

The propagation of thermal waves at finite speed is analyzed both for processes which fulfill the local equilibrium hypothesis and for processes which do not fulfill this hypothesis. A modified form of the Cattaneo-Vernotte constitutive equation for the heat-flux-density vector is proposed. The constitutive equation does not require the definition of a thermodynamic temperature field for local nonequilibrium states and, for a homogeneous medium, relates the heat-flux-density vector to the internal-energy distribution. The proposed model is applied to investigate the propagation of axisymmetric thermal waves in an infinite solid medium.

Scalar Fluctuations from Extended Non-equilibrium Thermodynamic States

In the framework of extended non-equilibrium thermodynamics, the local non-equilibrium state of a liquid is described by the density, temperature, and a structural variable, ζ, and its rate-of-change. ζ is the ensemble average of a function A (Q) of the configuration co-ordinates, and it is assumed to relax to local equilibrium in a time short compared to the time for diffusion of an appreciable number of particles into the system. By a projection operator technique of Grabert, an equation is derived from the Liouville equation for the distribution of fluctuations in TV, the particle number, and in A and Ȧ. An approximate solution is proposed which exhibits nonequilibrium corrections to the Einstein function in the form of a sum of thermodynamic forces. For a particular structural model, the corresponding non-Einstein contributions to correlation functions are estimated to be very small. For variables of the type considered here, the thermodynamic pressure is found to equal the pressure trace.