Minimum Entropy Production Research Articles

Turbulent forced convection and entropy production of a nanofluid in a solar collector considering various shapes for nanoparticles

In the current study, the two-phase mixture model is employed to assess the influences of nanoparticle shape on the hydrothermal aspects and entropy production of turbulent forced convection of MoS2/water nanofluid (NF) flow through a flat plate solar collector. The considered nanoparticle shapes include blade, brick, platelet and cylinder. The studied performance features include the heat transfer, outlet fluid temperature, pressure loss, friction factor, performance evaluation criterion (PEC) and entropy production. In addition, the effect of volume fraction of nanoparticles (ϕ) on the above-mentioned parameters is evaluated at two different NF mass flow rates (ṁ). According to the results, the maximum PEC corresponds to the case of ϕ = 3%, ṁ = 0.5 kg/s and brick-shaped nanoparticles, while the minimum entropy production corresponds to the case of φ = 4%, ṁ = 0.5 kg/s and blade-shaped ones.

Can the law of maximum entropy production describe the field-induced orientation of ellipsoids of rotation?

Electrostatic approaches are successful in explaining the experimentally observed field-induced orientations of the axis with the highest Clausius-Mossotti factor. For conductive or nonconductive, prolate or oblate spheroids, this is always the longest axis when different frequency-dependent dispersions of their effective conductivity along the three principal axes are neglected. Here, it is shown that these orientations correspond to the ‘law of maximum entropy production’ (LMEP) by comparing the axes-ratio dependencies of the torques calculated with the electrostatic approach with the effective conductivity differences between a suspension with field-oriented and randomly oriented objects. At low volume fraction, the obtained conductivity differences, which enter the LMEP, predict almost exactly the torque curves when plotted over axis ratio of the objects. Since the field-induced orientation at constant field strength increases the effective conductivity, the suspension system obviously does not behave according to the Prigogine principle, which would demand the minimization of energy dissipation and entropy production through object orientation. However, the Prigogine principle requires the suspension system to be close to equilibrium in its linear range. These conditions must be rejected if the LMEP is to be applied. Apparently the LMEP provides a phenomenological criterion for axis orientation, even though it is not yet clear whether and how increased conductivity, power dissipation and entropy production can also be introduced as driving forces at the single object level. However, the results also indicate that the disregard of energy dissipation may not be a problem in the electrostatic description of field-induced object orientation.

Semitheoretical formulation of annular flow void fraction using the principle of minimum entropy production

The two-phase flow void fraction is a critical parameter for characterising the pressure drop as well as heat and mass transfer capability of the working fluid within thermal systems, the accurate estimation of which drives heat exchanger design and control optimisation. A semitheoretical expression for the void fraction of two-phase flows, also applicable to small-sized channels, is obtained from an analytical study based on the principle of minimum entropy production and the introduction of empirical coefficients to be fitted to experimental data available in the open literature. These coefficients embody the importance of the simplified physical terms of this formulation while recovering the accuracy loss owing to nonlinear phenomena, heat and mass transfer, and three-dimensional effects. By accounting for surface tension, this model generalises previous theories and describes the influence of smaller-sized channels in terms of the stable void fraction. This mathematical framework can be used to summarise data covering different refrigerants, channel diameters, and operating conditions.

Theoretical study on regular reflection of shock wave–boundary layer interactions

Abstract

Entropy production minimization and non-Darcy resistance within wavy motion of Sutterby liquid subject to variable physical characteristics

Non-Darcy resistance in peristaltic transport of Sutterby liquid in curved configuration is modeled. Variable characteristics of material (i.e., thermal conductivity and viscosity) are taken as temperature-dependent. Soret and Dufour features have also been retained. Problem is modeled by using conservation laws. Long wavelength and small Reynolds number have been invoked. Resulting problems have been solved numerically. Entropy optimization analysis is made. Axial velocity, temperature, concentration, entropy, Bejan number and heat transfer rate are examined for influential variables. It is found that velocity increases for variable viscosity coefficient and porous-space parameter. Temperature decreases for increased values of variable thermal conductivity. Opposite behavior of mass and energy is noted for Soret and Dufour parameters. Entropy minimized for thermal conductivity and viscosity coefficients. Entropy enhancement is noticed for Soret and Dufour parameters. Heat transfer rate at upper wall is enhanced for Soret and Dufour variables.

Entropy generation minimization and nonlinear heat transport in MHD flow of a couple stress nanofluid through an inclined permeable channel with a porous medium, thermal radiation and slip

AbstractIrreversible losses and heat transport in a magnetohydrodynamic flow of a viscous, steady, incompressible, and fully developed couple stress Al2O3–water nanofluid through a sloping permeable wall channel with porous medium and under the effect of radiation heat flux and slip were analyzed. The fundamental equations were solved numerically by using Runge‐Kutta together with the shooting technique and the results were in qualitative agreement with an exact solution obtained for a limit case. The impacts of couple stress, Darcy number, solid nanoparticle concentrations, conduction‐radiation parameter, Hartmann number and hydrodynamic slip on flow, temperature, heat transport, and entropy production were examined. It was possible to achieve values of minimum entropy production not yet reported in previous studies. In this way, optimal values of couple stress and slip were obtained. The heat transport was also explored and optimal values of slip flow and conduction‐radiation parameter with maximum heat transfer were found. Finally, in addition to the alumina, the distributions of velocity, temperature, and entropy generation in TiO2–water and Cu–water were presented for different solid nanoparticle concentrations. It was obtained that the local entropy of TiO2–water was lower than Cu–water and Al2O3–water in the channel bottom region while it was greater in the upper region.

Coupling loss at the end connections of REBCO stacks: 2D modelling and measurement

In high power density superconducting motors, superconducting tapes are usually stacked and connected together at terminals to improve the current capacity. When a parallel sinusoidal magnetic field is applied on this partially coupled stack, the coupling current is induced and causes additional coupling loss. Usually 3D modeling is needed to calculate the coupling loss but it takes too much computing resource and time. In this paper, a numerical 2D modeling by minimum electromagnetic entropy production (MEMEP) method is developed to speed up the calculation. The presented MEMEP model shows good accuracy and the capability to take the realistic resistance between tapes into account for coupling loss calculation with a high number of mesh element, which agrees to measurements.Thanks to the model, a systemic study of coupling loss on amplitude-dependence, frequency-dependence, resistance-dependence, and length-dependence, is presented and discussed. The results reveal the features of coupling loss which is very helpful devices with multi-tape conductors, such as the stator or rotor windings of motors.

Thermodynamics of computing with circuits

Digital computers implement computations using circuits, as do many naturally occurring systems (e.g., gene regulatory networks). The topology of any such circuit restricts which variables may be physically coupled during the operation of the circuit. We investigate how such restrictions on the physical coupling affects the thermodynamic costs of running the circuit. To do this we first calculate the minimal additional entropy production that arises when we run a given gate in a circuit. We then build on this calculation, to analyze how the thermodynamic costs of implementing a computation with a full circuit, comprising multiple connected gates, depends on the topology of that circuit. This analysis provides a rich new set of optimization problems that must be addressed by any designer of a circuit, if they wish to minimize thermodynamic costs.

Robotic Unicycle Intelligent Robust Control Pt I: Soft Computational Intelligence Toolkit

The concept of an intelligent control system for a complex nonlinear biomechanical system of an extension cableless robotic unicycle discussed. A thermodynamic approach to study optimal control processes in complex nonlinear dynamic systems applied. The results of stochastic simulation of a fuzzy intelligent control system for various types of external / internal excitations for a dynamic, globally unstable control object - extension cableless robotic unicycle based on Soft Computing (Computational Intelligence Toolkit - SCOptKBTM) technology presented. A new approach to design an intelligent control system based on the principle of the minimum entropy production (minimum of useful resource losses) determination in the movement of the control object and the control system is developed. This determination as a fitness function in the genetic algorithm is used to achieve robust control of a robotic unicycle. An algorithm for entropy production computing and representation of their relationship with the Lyapunov function (a measure of stochastic robust stability) described.

Flow Field Patterns for Proton Exchange Membrane Fuel Cells

Flow field designs for the bipolar plates of the proton exchange membrane fuel cell are reviewed; including the serpentine, parallel, interdigitated, mesh type or their mixtures, furthermore 2D circular and 3D tubular geometries, porous, fractal and biomimetic flow fields. The advantages / disadvantages and tendencies from field optimizations are discussed. The performance of each flow field design is compared to the conventional serpentine flow field. Good flow field plates give uniform gas distributions, low pressure drop for transport and sufficient rib area to provide high electronic conductivity. A good field should also prevent water condensation, remove water efficiently, and provide sufficiently high moisture content in the membrane. The demands on design are sometimes contradictory. Future work should aim for a flow field geometry and topology that produces uniform gas delivery at a low pressure-drop, and at the same time has an optimal channel shape for better water removal. It is concluded that for an area-filling gas distributor, the developments should aim to find a flow field in accordance with minimum entropy production, making an emphasis on multi-criteria optimization methods.

Information geometry aspects of minimum entropy production paths from quantum mechanical evolutions.

We present an information geometric analysis of entropic speeds and entropy production rates in geodesic evolution on manifolds of parametrized quantum states. These pure states emerge as outputs of suitable su(2;C) time-dependent Hamiltonian operators used to describe distinct types of analog quantum search schemes. The Riemannian metrization on the manifold is specified by the Fisher information evaluated along the parametrized squared probability amplitudes obtained from analysis of the temporal quantum mechanical evolution of a spin-1/2 particle in an external time-dependent magnetic field that specifies the su(2;C) Hamiltonian model. We employ a minimum action method to transfer a quantum system from an initial state to a final state on the manifold in a finite temporal interval. Furthermore, we demonstrate that the minimizing (optimum) path is the shortest (geodesic) path between the two states and, in particular, minimizes also the total entropy production that occurs during the transfer. Finally, by evaluating the entropic speed and the total entropy production along the optimum transfer paths in a number of physical scenarios of interest in analog quantum search problems, we show in a clear quantitative manner that to a faster transfer there corresponds necessarily a higher entropy production rate. Thus we conclude that lower entropic efficiency values appear to accompany higher entropic speed values in quantum transfer processes.

Minimum entropy production in a distillation column for air separation described by a continuous non-equilibrium model

In this work, we apply the rate-based model of Taylor and Krishna to describe the separation of air in a low-pressure, packed distillation column. By use of numerical optimization, we identify the temperature profile for heat exchange with the column and its surroundings that minimizes the total entropy production. Optimal operation of the column reduces the entropy production by nearly 50%, and the total heating- and cooling duties by 30% and 50%, respectively. We find that the local entropy production is more uniform for the optimal solution than in the adiabatic column, a property that may be helpful for new designs. Using the equilibrium stage model, the state of minimum entropy production has higher cooling/heating duties than in the rate-based model case. This shows that more sophisticated models can be beneficial for the development of reliable strategies to improve the energy efficiency of distillation columns.

Modeling of airgap influence on DC voltage generation in a dynamo-type flux pump

High-temperature superconducting (HTS) flux pumps are promising devices to maintain steady current mode in HTS magnets or to energize rotor windings in motors and generators in a contactless way. Among different types of flux pumps, the dynamo-type flux pump has been very common due to its simple structure and ease of maintenance. However, understanding the principle of dynamo-type flux pump has been challenging despite the recent progress. This article employs an efficient numerical model based on minimum electromagnetic entropy production method to analyze the performance of the flux pump in open-circuit mode. This model is much faster and efficient than previous works on flux pumps. In addition to the main behavior of the flux pump, this work investigates the influence of airgap and critical current density on open-circuit DC voltage of the flux pump. We compare the modeling results of open-circuit DC voltage for different airgaps to experimental ones obtained in (Bumby et al 2016 Appl. Phys. Lett. 108 122601), showing good agreement. Modelling results show that with increasing airgap, pumping voltage in the superconducting tape does not cease, but only reaches to insignificantly low values, which is not measurable via experiments. In addition, the voltage in open-circuit does not depend on the critical current density, as long as the superconducting tape is fully saturated with screening currents.

Numerical study of entropy production minimization in Bödewadt flow with carbon nanotubes

This work aims to analyze three-dimensional Bödewadt nanofluid flow. An infinite disk in Bödewadt flow is stationary while fluid very far away from the disk rotates with uniform angular velocity. Water and kerosene oil are treated as base liquids. Both single-wall (SWCNTs) and multiple-wall (MWCNTs) carbon nanotubes are employed. Viscous dissipation effect is addressed. Entropy generation is analyzed by implementing second law of thermodynamics. The governing non-linear PDEs are converted into non-dimensional ODEs using transformation process. Shooting technique subject to Runge–Kutta fifth order algorithm (bvp4c) is implemented for the solution process. Velocities (radial, tangential and axial), temperature, entropy production rate, Bejan number, skin friction and Nusselt number are addressed for impact of involved variables. Velocity components (axial, radial and tangential) intensify with higher nanoparticle volume fraction while it reduces for higher ratio of radial stretching rate to rotation rate parameter. Enlargement in temperature of fluid is observed against higher estimations of nanoparticle volume fraction, Eckert number and ratio of radial stretching rate to rotation rate parameter. Entropy production rate is minimized via higher nanoparticle volume fraction. Bejan number is an increasing function of Eckert number, ratio of radial stretching rate to rotation rate parameter and nanoparticle volume fraction. Higher values of ratio of radial stretching rate to rotation rate parameter and nanoparticle volume fraction lead to an increment in Nusselt number. Moreover impact of multiple-wall CNT is efficient when compared with single-wall CNT.

Morphology of the Macrocrystals of Minerals: Empirical Principle of Complete Faceting

An empirical principle of complete faceting of crystals, implemented during evolution of their free shape in nature, has been formulated: the set of polyhedra that can be used to describe the free shape of macrocrystals of minerals tends to the class of holohedral morphological types, formed by the symmetry-equivalent surfaces dominant on the crystal, and their probabilities cease to depend on time. This principle, which is applicable both to the growth forms and crystal dissolution, is a macroscopic consequence of the main principle of nonequilibrium thermodynamics: the tendency of an open system to the minimum production of entropy.

Errata: Formulation of steady-state void fraction through the principle of minimum entropy production [Journal of Thermal Science and Technology (2020jtst0025)

Errata: Formulation of steady-state void fraction through the principle of minimum entropy production [Journal of Thermal Science and Technology (2020jtst0025)

Formulation of steady-state void fraction through the principle of minimum entropy production

Formulation of steady-state void fraction through the principle of minimum entropy production

Seeking minimum entropy production for a tree-like flow-field in a fuel cell.

Common for tree-shaped, space-filling flow-field plates in polymer electrolyte fuel cells is their ability to distribute reactants uniformly across the membrane area, thereby avoiding excess concentration polarization or entropy production at the electrodes. Such a flow field, as predicted by Murray's law for circular tubes, was recently shown experimentally to give a better polarization curve than serpentine or parallel flow fields. In this theoretical work, we document that a tree-shaped flow-field, composed of rectangular channels with T-shaped junctions, has a smaller entropy production than the one based on Murray's law. The width w0 of the inlet channel and the width scaling parameter, a, of the tree-shaped flow-field channels were varied, and the resulting Peclet number at the channel outlets was computed. We show, using 3D hydrodynamic calculations as a reference, that pressure drops and channel flows can be accounted for within a few percents by a quasi-1D model, for most of the investigated geometries. Overall, the model gives lower energy dissipation than Murray's law. The results provide new tools and open up new possibilities for flow-field designs characterized by uniform fuel delivery in fuel cells and other catalytic systems.

Evolution of Agricultural Technologies: from “Gray” to “Green”

The evolution of agricultural technologies in the development of human civilization is considered. Based on this example, it is shown that a new stage in soil cultivation technology began in the 20th century. It is associated with the transition from extensive “gray” technologies for the management of natural resources, which are strictly oriented only by momentary economic feasibility, to nontraditional (“nature-based”) “green” farming technologies. A natural transition has taken place from the strategy of its development based on Ziegler’s principle of maximum entropy production to Prigogine’s strategy of minimum entropy production, which is based on the rationalization of the use of available resources for a dissipative structure on the planet, such as the human population. The foundation for the rationalization is nature-based technology for human use of natural resources. The theoretical justification of the inevitability of “green farming” is confirmed by the example of a long-term biosphere experiment on the development of agricultural technologies. This type of farming is characterized by a more economical method of tillage: partial or complete rejection of soil-turn plowing, the absence of vertical mixing of the arable layer, minimal disturbance of the soil cover by agricultural machines, and mandatory soil mulching (“no-till” or “mulch tillage”) in order to preserve the soil moisture and reduce soil erosion. The no-till soil processing system, i.e., the absence of interference in the natural processes of soil formation, is a modern farming system in which the soil is not processed and its surface is covered with specially crushed plant residues (mulch). It is illustrated that the no-till technology of direct sowing and mulching is currently being introduced in various regions of the planet with shallow, surface loosening or even complete rejecting tillage. It is shown that the application of the green farming technologies leads to rationalization of the use of not only energy and soil resources but also water resources, for which the situation is becoming increasingly tense for human civilization.

Numerical simulation of nanofluid convective heat transfer in an oblique cavity with conductive edges equipped with a constant temperature heat source: Entropy production analysis

In the present work, the entropy production of Al2O3-water nanofluid in an oblique cavity enclosure is examined. The side edges of the enclosure are at lower temperature and the top and down ones are insulated. Two thick conductive walls are placed on the low temperature edges. Furthermore, the center of the enclosure is equipped with a constant high temperature heat source. The enclosure is exposed to an inclined magnetic field. The governing nonlinear partial differential equations are continuity, Navier–Stokes and energy equations. These equations are solved using an open-source CFD software package (OpenFOAM). The influence of effective parameters includes Ra number, Hartman number, the angles of magnetic field and enclosure, nanoadditives concentration, and aspect ratio on the entropy production and the Bejan (Be) number are investigated. The results show that the minimum entropy production happened at low power magnetic fields. With the increase of the slope of the cavity, the entropy production rises. The addition of nanoadditives leads to an intensification in the entropy production and a reduction in the Be number.