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Abstract

We use the Shannon (information) entropy to define an “entropic” temperature for 1D nonequilibrium system with heat flux. In contrast to the kinetic temperature, which is related to the average kinetic energy, the nonequilibrium entropic temperature is related to the changes in entropy and serves as a criterion for thermalization. However, the direction and value of the heat flux is controlled by the gradient of the kinetic temperature, whereas space-time evolution and the space-time evolution of the heat flux are governed by the hyperbolic heat conduction equation. The extended nonequilibrium variables, namely, entropy, entropic temperature, thermal conductivity, and heat capacity demonstrate a third-law-like behavior at high deviation from equilibrium when the heat flux tends to its maximum value, even at nonzero value of the kinetic temperature. The ratio of the heat flux to its maximum possible value plays a role of an order parameter – it varies from zero in the equilibrium (disordered) state to unity in the nonequilibrium (ordered) state.

Abstract

Thermodynamic performance analysis of microscopic Feynman’s engine has always been a hot topic, since it can reveal the operating mechanism of the system and give out the suggestions of performance improvement. The present work explores the optimal performance regions of the ratchet operating, respectively, as heat engine and refrigerator. The major purpose is to obtain the optimal performance bunds and provide theoretical guidelines for the designs of practical microscopic ratchet engine systems. Based on an irreversible Feynman’s ratchet engine, the optimal power output versus thermal efficiency performance and the optimal cooling load versus COP performance in different operation modes are analyzed. The effects of irreversible heat leakage and major design parameters are also explored. By further introducing the ecological function, efficient power, and figure of merit criteria, performance characteristics of ratchet device with different optimization indexes are analyzed and compared with each other. The optimal performance regions concerning different optimization criteria are obtained. The results show that by reasonably selecting design parameters, Feynman’s ratchet can attain the optimal operation conditions for different design purposes.

Abstract

Momentum and thermal transport through open-celled metallic foams filled in a channel of small height is studied in the present technical brief. Fully developed momentum and thermal layers via the Brinkman–Darcy model enable us to obtain closed-form solutions regarding the fluid velocity and temperature distributions of metal and fluid, all depending upon a factor related to the wall slip velocity. A comparative study on the pertinent physical parameters helps us conclude that the wall slip cools the porous channel, enhancing the rate of heat transfer. In addition to this, increasing pore density leads to an effective reduction in the entropy generation number, followed by further reduction with the nonzero slip velocity, except the near-wall regions.

Abstract

The question of frame-indifference of the thermomechanical models has to be addressed to deal correctly with the behavior of matter undergoing finite transformations. In this work, we propose to test a spacetime formalism to investigate the benefits of the covariance principle for application to covariant modeling and numerical simulations for finite transformations. Several models especially for heat conduction are proposed following this framework and next compared to existing models. This article also investigates numerical simulations using the heat equation with two different thermal dissipative models for heat conduction, without thermomechanical couplings. The numerical comparison between the spacetime thermal models derived in this work and the corresponding Newtonian thermal models, which adds the time as a discretized variable, is also performed through an example to investigate their advantages and drawbacks.

Abstract

The main aim of this research work is to show the simultaneous effects of ferro-particles (Fe3O4) and thermal radiation on the natural convection of non-Newtonian nanofluid flow between two vertical flat plates. The studied nanofluid is created by dispersing ferro-particles (Fe3O4) in sodium alginate (SA), which is considered as a non-Newtonian base fluid. Resolution of the resulting set of coupled non-linear second order differential equations characterizing dynamic and thermal distributions (velocity/temperature) is ensured via the Adomian decomposition method (ADM). Thereafter the obtained ADM results are compared to the Runge–Kutta–Feldberg based shooting data. In this investigation, a parametric study was conducted showing the influence of varying physical parameters, such as volumic fraction of Fe3O4 nanoparticles, Eckert number (Ec) and thermal radiation parameter (N), on the velocity distribution, the skin friction coefficient, the heat transfer rate and the temperature distribution. Results obtained also show the advantages of ferro-particles over other types of standard nanoparticles. On the other hand, this investigation demonstrates the accuracy of the adopted analytical ADM technique.

Abstract

In this study, the effect of magnetic field on an incompressible ferrofluid flow along a vertical wavy surface saturated in a porous medium is investigated. Ferrofluid is made by incorporating magnetic particles, in this case cobalt, at the nanoscale level into a base fluid. For the study of porous medium two well-known models, namely, Darcy and non-Darcy, are used. The mathematical model in terms of governing partial differential equations which are based on conservation laws in mechanics according to the assumption is developed, and this model is converted into a dimensionless form by suitable transformations. Due to the complex non-linear partial differential equations, the numerical solution is calculated by using an implicit finite difference scheme. The impact of involved parameters, namely, magnetic parameter, nanoparticle volume fraction parameter, the amplitude of the wavy surface, and the Grashof number, on Nusselt and average Nusselt numbers are studied through graphs and tables.

The results show that for large values of the magnetic parameter, both the Nusselt number and the average Nusselt number decrease in ferrofluid flow. The value of the Nusselt number in the Darcy model is higher than the value of the Nusselt number in the non-Darcy model.

Abstract

First, the special-relativistic Theory of Irreversible Processes for a multi-component fluid is formulated. It is based on (i) the balance equations of the particle number and the energy-momentum for the total system (i. e., the mixture of the components) as well as the sub-systems (i. e., the components) and (ii) the dissipation inequality and the Gibbs equation for the mixture. In order to allow for reactions between the single components, in contrast to the total system, the sub-systems are assumed to be open, which means that their particle number and energy-momentum are not constrained by conservation laws. Without making any assumptions on the thermodynamic behavior of the interacting components, one arrives at a thermodynamic description of the mixture showing now heat conduction and viscosity. In particular, this makes it possible to calculate the entropy production and, thus, to identify thermodynamic currents and forces. In a second part, the post-Newtonian limit of this theory is calculated to show that for the mixture there result relations known from classical Extended Thermodynamics that partly are corrected by entrainment terms. The mathematical origin and physical consequences of these terms are discussed.

Abstract

In order to meet the current challenges in the fabrication of nanobiomaterials and enhancement of thermal extrusion systems, current theoretical continuation is targeted at the rheology of couple stress nanofluid by exploiting activation energy, porous media, thermal radiation, gyrotactic micro-organisms, and convective Nield boundary conditions. The heat and mass performances of nanofluid are captured with an evaluation of the famous Buongiorno model, which enables us to determine the attractive features of Brownian motion and thermophoretic diffusion. The couple stress fluid is beneficial to examine multiple kinds of physical problems because this fluid model has the capability to describe the rheology of various complex fluids, e. g., fluids having long-chain molecules as a polymeric suspension, liquid crystals, lubricants, and human and animal blood. Simultaneous behavior of the magnetic field and porosity are studied with thermal radiation effects. The distribution of velocity has been conducted by using second-order velocity slip (Wu’s slip) and activation energy features. For the dimensionless purpose, the similarity variable has been initiated, and the modeled equations are renovated sufficiently. A famous shooting method is used to determine the numerical solutions, and accurate results have been obtained. A variety of critical flow parameters is graphically illustrated with physical significance.

Abstract

Non-equilibrium thermodynamics provides a general framework for the description of mass and thermal diffusion, thereby including also cross-thermal and material diffusion effects, which are generally modeled through the Onsager coupling terms within the constitutive equations relating heat and mass flux to the gradients of temperature and chemical potential. These so-called Soret and Dufour coefficients are not uniquely defined, though, as they can be derived by adopting one of the several constitutive relations satisfying the principles of non-equilibrium thermodynamics. Therefore, mass diffusion induced by a temperature gradient and heat conduction induced by a composition gradient can be implicitly, and unexpectedly, predicted even in the absence of coupling terms. This study presents a critical analysis of different formulations of the constitutive relations, with special focus on regular binary mixtures. It is shown that, among the different formulations presented, the one which adopts the chemical potential gradient at constant temperature as the driving force for mass diffusion allows for the implicit thermo-diffusion effect to be strictly absent while the resulting Dufour effect is negligibly small. Such a formulation must be preferred to the other ones since cross-coupling effects are predicted only if explicitly introduced via Onsager coupling coefficients.

Abstract

In this work, the effect of temperature-dependent thermal conductivity (k(T)) and viscosity (μ(T)) variation on entropy generation in circular channels with an approach from macro- to micro-scale is numerically investigated. Thermally as well as hydrodynamically fully developed flow of water through the fixed length channels with constant total heat flow rate and total mass flow rate is considered. The effects of k(T) variation and μ(T) variation on entropy generation are analyzed individually as well as collectively. It is observed that in the case of Constant Property Solutions (CPS) Sgen,tot is maximum at the macro-level; however, in the case of combined k(T) and μ(T) variations it is maximum at the micro-level. The Bejan number (Be) and irreversibility distribution ratio (φ) are also calculated for asserting the dominance of frictional irreversibility and conduction heat transfer irreversibility. Additionally, the optimum diameter (D) corresponding to the optimum number of channels is calculated at minimum total entropy generation. It is observed that D is minimum for k(T) variation followed by CPS, μ(T) variation, and combined k(T) and μ(T) variations.