Hasil untuk "Thermodynamics"

Erhan Huang, Ying Chang, Yangzhao Liu et al.

Heliostats constitute essential elements within concentrating solar power (CSP), where their structure, load profiles, and operational environment render wind loads a critical factor in their design considerations, as these loads directly impact the cost of energy generation. The aerodynamics significantly influence wind-induced effects, resulting in considerable variability in wind loads among different heliostat geometries. This study utilizes the Computational Fluid Dynamics (CFD) methodology to systematically examine the aerodynamic behavior of an isolated pentagonal heliostat. Employing the Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations with an atmospheric boundary layer inlet condition, the investigation focuses on the flow field and wind load characteristics at four representative pitch angles: 0° (stow position), 30°, 60°, and 90°. Findings indicate that the pitch angle exerts a decisive impact on flow separation patterns. Specifically, as the elevation angle decreases, the flow regime shifts from being predominantly influenced by the mirror surface to being governed by the support structure, mediated through an interactive coupling between these components. At the 60° operational pitch angle, the pentagonal heliostat’s distinctive corner geometry induces an asymmetric vortex configuration—characterized by a smaller vortex at the top and a larger one at the bottom—thereby disrupting the conventional vortex distribution observed in symmetric heliostat designs. A further analysis of wind load characteristics indicates that, compared to a quadrilateral heliostat, the pentagonal mirror exhibits a significantly lower Elevation Moment Coefficient, despite a slight increase in the normal force coefficient. This reduction is attributed to a balancing mechanism: the “vortex structure asymmetry” creates an upper-large–lower-small distribution of absolute negative pressure on the support surface, while the “stagnation point position” shift with elevation angle produces an upper-small–lower-large distribution of absolute positive pressure on the reflector. The interaction between these opposing trends minimizes the net pressure differential across the mirror height, thereby contributing to superior overall aerodynamic performance. The reduction in the elevation moment coefficient contributes to enhanced structural wind resistance, thereby improving the overall energy efficiency and economic viability of concentrating solar power.

Eirini Sourtzinou, Charis Anastopoulos

This paper is part of a bottom-up approach to gravitational thermodynamics that is guided by the axiomatic frameworks of equilibrium thermodynamics. We identify a novel form of the microcanonical distribution for systems in background gravitational fields that respects the kinetic theory and the thermodynamic symmetries. Thermodynamic consistency dictates the treatment of the gravitational field as a thermodynamic variable. We introduce the thermodynamic conjugate to the gravitational field, the gravitational pull, an additive variable that is a structural element of our microcanonical distribution. We demonstrate the validity of our results to inhomogenous background fields, a class of self-gravitating systems, relativistic gases in Rindler spacetime, and quantum gases.

Akshay Balsubramani

We develop the laws of thermodynamics in terms of general exponential families. By casting learning (log-loss minimization) problems in max-entropy and statistical mechanics terms, we translate thermodynamics results to learning scenarios. We extend the well-known way in which exponential families characterize thermodynamic and learning equilibria. Basic ideas of work and heat, and advanced concepts of thermodynamic cycles and equipartition of energy, find exact and useful counterparts in AI / statistics terms. These ideas have broad implications for quantifying and addressing distribution shift.

Maite Arcos, Philippe Faist, Takahiro Sagawa et al.

In thermodynamics, an agent's ability to extract work is fundamentally constrained by their environment. Traditional frameworks struggle to capture how strategic decision-making under uncertainty, particularly an agent's tolerance for risk, determines the trade-off between extractable work and probability of success in finite-scale experiments. Here, we develop a framework for nonequilibrium thermodynamics based on adversarial resource theories, in which work extraction is modeled as an adversarial game for an agent extracting work. Within this perspective, we consider a Szilard-type engine as a game isomorphic to Kelly gambling, an information-theoretic model of optimal betting under uncertainty -- but with a thermodynamic utility function. Extending the framework to finite-size regimes, we apply a risk-reward trade-off to find an interpretation of the Renyi divergences in terms of extractable work for a given failure probability. By incorporating risk sensitivity via utility functions, we show that the guaranteed amount of work a rational agent would accept instead of undertaking a risky protocol is given by a Renyi divergence. This provides a unified picture of thermodynamics and gambling, and highlights how generalized free energies emerge from an adversarial setup.

Nikolaos Lampropoulos, Alexandros Vouros, Ioannis Templalexis et al.

A study on aerodynamic design studies of a blended wing–body (BWB) unmanned aerial vehicle (UAV) operating at low Mach numbers is presented. First, a parametric investigation based on analytical equations is carried out to identify the range of the necessary wetted area for the UAV to maximize endurance at a Mach number close to 0.1. A base-of-reference configuration is designed, and its aerodynamic performance is evaluated by utilizing a panel method in Xflr5. An optimization algorithm is then incorporated to trim the UAV and produce the ‘clean’ configuration. Computational fluid dynamics (CFD) simulations are performed within the OpenFoam environment to produce first the updated drag polars, and then, to analyze the integration of the nacelle and the pair of electric ducted fans (EDFs) used for the propulsion system. In particular, when examining the integration of the nacelle with a spinning electric ducted fan (EDF) standing as the propulsion system of the vehicle, a rotating, sliding mesh computational approach is adopted. Results indicate that the clean configuration is characterized by strong longitudinal stability so that the UAV has the potential to fly trimmed at very low speeds. Mounting EDFs on the back of the fuselage is conducive to higher loading with minimal drag penalty. An increased lift-to-drag ratio is achieved. Reduced wake mixing due to the EDF’s jet flow is observed. The spanwise flow that is conducive to pitch brake and loss of stability is also weak, as the suction produced by the EDF diverts the flow inboard.

Stefania Moioli, Valentina Schiattarella

Carbon Capture, Utilization and Storage (CCUS) is a topic of interest for its relevance in decreasing the emissions to the atmosphere of CO2, a powerful greenhouse gas, related to the industrial production and power generation by fossil fuels. Aqueous amine solutions can be used as chemical solvents for this aim, though the high energy consumption and the related operating costs, their toxicity and the corrosion issues related to their use do not favor their application on the large scale. The research on novel solvents for CO2 removal, that could overcome the disadvantages of the traditional solvents, requires the analysis of phase equilibria of systems for which physical-chemical properties cannot be found in detail in the literature. In particular, the solubility of gases, mainly CO2, in the mixture to be considered, is fundamental to understand the suitability of a new species as solvent for chemical or physical absorption. With the aim of overcoming the issues due to the lack of experimental data on novel systems, an experimental unit has been installed at the Process Thermodynamics laboratory (PT lab) of Politecnico di Milano aimed at collecting data of solubility and diffusivity of gases into low volatile liquids that could be used as solvents for CO2 capture. A detailed specific experimental procedure has been defined and the unit has been firstly operated for validation, by collection of solubility data of CO2 into a 30% wt. MonoEthanolAmine (MEA) solvent, one of the most developed solvents already industrially used. Both the conditions of the absorption section and of the regeneration section, operating at different temperatures, have been considered. Then, the description of the equilibrium attained in the experimental unit has been carried out, taking into account different thermodynamic models and selecting the one best describing the system.

Florian Pape, Belal G. Nassef, Stefan Schmölzer et al.

Metalworking fluids (MWFs) are crucial in the manufacturing industry, playing a key role in facilitating various production processes. As each machining operation comes with distinct requirements, the properties of the MWFs have to be tailored to meet these specific demands. Understanding the properties of different MWFs is fundamental for optimizing processes and improving performance. This study centered on characterizing the thermal behavior of various cutting oils and water-based cutting fluids over a wide temperature range and sheds light on the specific tribological behavior. The results indicate that water-based fluids exhibit significant shear-thinning behavior, whereas cutting oils maintain nearly Newtonian properties. In terms of frictional performance, cutting oils generally provide better lubrication at higher temperatures, particularly in mixed and full-fluid film regimes, while water-based fluids demonstrate greater friction stability across a wider range of conditions. Among the tested fluids, water-based formulations showed a phase transition from solid to liquid near 0 °C due to their high water content, whereas only a few cutting oils exhibited a similar behavior. Additionally, the thermal conductivity and heat capacity of water-based fluids were substantially higher than those of the cutting oils, contributing to more efficient heat dissipation during machining. These findings, along with the reported data, intend to guide future researchers and industry in selecting the most appropriate cutting fluids for their specific applications and provide valuable input for computational models simulating the influence of MWFs in the primary and secondary shear zones between cutting tools and the workpiece/chiplet.

Baydır Ayşegül Türk

Increasing drug pollution represents a substantial risk to the safeguarding of water resources. Favipiravir, a commonly used antiviral medication, is one of the pharmaceutical residues found in wastewater and poses a threat to the ecosystem. Favipiravir is classified as Category 2 for germ cell mutagenicity and reproductive toxicity and is a drug suspected of leading to genetic abnormalities and adverse effects on the developing fetus. In this study, hazelnut shell-derived activated carbon was utilized as an adsorbent for the removal of favipiravir from aqueous solutions. First, the produced activated carbon was characterized through various analyses. Then, during the adsorption process, key parameters such as initial favipiravir concentration, adsorbent dosage, solution pH, contact time, and temperature were optimized. The process was analyzed based on equilibrium, kinetics, and thermodynamics. Optimum conditions (30 μg/mL initial concentration, 15 mg adsorbent dose, 90 min contact time, pH 2) were determined, and the highest adsorption efficiency of 94.60% was obtained under these conditions. The adsorption mechanism was most accurately by the pseudo-second-order rate model (R²: 0.9998) and the Langmuir adsorption model (R 2: 0.9942). Moreover, thermodynamic studies have shown that the mechanism is spontaneous since the free energy change (ΔG < 0), exothermic since the enthalpy change (ΔH < 0), and the entropy change (ΔS < 0) reduce the disorder in the system. This study emphasizes the adsorbent’s potential as a green and economical treatment solution.

David S. Pereira, João Ferraz, Francisco S. N. Lobo et al.

This review delves into the pivotal primordial stage of the universe, a period that holds the key to understanding its current state. To fully grasp this epoch, it is essential to consider three fundamental domains of physics: gravity, particle physics, and thermodynamics. The thermal history of the universe recreates the extreme high-energy conditions that are critical for exploring the unification of the fundamental forces, making it a natural laboratory for high-energy physics. This thermal history also offers valuable insights into how the laws of thermodynamics have governed the evolution of the universe's constituents, shaping them into the forms we observe today. Focusing on the Standard Cosmological Model (SCM) and the Standard Model of Particles (SM), this paper provides an in-depth analysis of thermodynamics in the primordial universe. The structure of the study includes an introduction to the SCM and its strong ties to thermodynamic principles. It then explores equilibrium thermodynamics in the context of the expanding universe, followed by a detailed analysis of out-of-equilibrium phenomena that were pivotal in shaping key events during the early stages of the universe's evolution.

T. L. Campos, M. C. Baldiotti, C. Molina

In the present work we study the construction of different thermodynamic descriptions for the Kerr-anti-de Sitter (KadS) black holes. The early versions of the KadS thermodynamics are briefly discussed, highlighting some of its strong points and shortcomings. Isohomogeneous transformations, a procedure for generating new thermodynamics, are presented and geometrically interpreted for KadS. This tool is used to determine possible KadS thermodynamics that can be constructed to satisfy a Smarr formula, and the validity of the first law in the generated thermodynamics. The connection between new thermodynamic theories and early Hawking's approach is considered. In this new framework, the usual KadS thermodynamics is complemented with its geometric construction, and Hawking's proposal, which does not satisfy the first law, is improved to an alternative thermodynamic theory. With the quantum statistical relation, Hawking's and this alternative KadS thermodynamics are also generalized from four to higher dimensions.

Jan Karbowski

This paper provides a perspective on applying the concepts of information thermodynamics, developed recently in non-equilibrium statistical physics, to problems in theoretical neuroscience. Historically, information and energy in neuroscience have been treated separately, in contrast to physics approaches, where the relationship of entropy production with heat is a central idea. It is argued here that also in neural systems, information and energy can be considered within the same theoretical framework. Starting from basic ideas of thermodynamics and information theory on a classic Brownian particle, it is shown how noisy neural networks can infer its probabilistic motion. The decoding of the particle motion by neurons is performed with some accuracy, and it has some energy cost, and both can be determined using information thermodynamics. In a similar fashion, we also discuss how neural networks in the brain can learn the particle velocity and maintain that information in the weights of plastic synapses from a physical point of view. Generally, it is shown how the framework of stochastic and information thermodynamics can be used practically to study neural inference, learning, and information storing.

Patrick Palmetshofer, Anne K. Geppert, Jonas Steigerwald et al.

Abstract We experimentally observe a new phenomenon, the formation of a toroidal region of lower film thickness in the center of the lamella formed during high Weber number water droplet impacts onto smooth heated walls. This region forms around the air bubble, which is entrapped during the initial impact phase at the impact center. Our study encompasses a variation of the droplet size, impact velocity, surface wettability and temperature. We show how this phenomenon can be explained considering a two-step process involving thermocapillary convection in two separate regions: The temperature gradient along the surface of the entrapped air bubble caused by heat conduction induces flow that pumps warmer liquid to the lamella-ambient interface due to the Marangoni effect. The non-uniform temperature distribution along it then causes fluid acceleration in the radial direction, depleting the fluid volume around the bubble in a self-amplifying manner. We use direct numerical simulations of a stagnant liquid film with an enclosed bubble at the wall to confirm this theory.

Mohammed Z. Alqarni, Mohamed Akel, Mohamed Abdalla

This manuscript focuses on new generalizations of <i>q</i>-Mittag-Leffler functions, called generalized hyper <i>q</i>-Mittag-Leffler functions, and discusses their regions of convergence and various fractional q operators. Moreover, the solutions to the <i>q</i>-fractional kinetic equations in terms of the investigated generalized hyper <i>q</i>-Mittag-Leffler functions are obtained by applying the <i>q</i>-Sumudu integral transform. Furthermore, we present solutions obtained as numerical graphs using the MATLAB 2018 program.

Miguel Cruz, Samuel Lepe

This work is devoted to the thermodynamics description of a phantom scenario proposed previously by the authors. The presence of negative chemical potential is unavoidable if we allege for a well defined thermodynamics framework since the cosmological model passages from phantom stage at present time to a future de Sitter evolution. As noted earlier in other works, we find that the negativity of the chemical potential is necessary to save phantom dark energy from thermodynamics inconsistencies.

Carlos H. S. Vieira, Jefferson L. D. de Oliveira, Jonas F. G. Santos et al.

Quantum thermodynamics seeks to extend non-equilibrium stochastic thermodynamics to small quantum systems where non-classical features are essential to its description. Such a research area has recently provided meaningful theoretical and experimental advances by exploring the wealth and the power of quantum features along with informational aspects of a system's thermodynamics. The relevance of such investigations is related to the fact that quantum technological devices are currently at the forefront of science and engineering applications. This short review article provides an overview of some concepts in quantum thermodynamics highlighting test-of-principles experiments using nuclear magnetic resonance techniques.

Marc Cozannet, Sébastien Le Guellec, Karine Alain

The number of methanogenesis substrates known to date has increased more than six-fold since the late 80s, bringing to 152 the number of proven substrates for methanogenesis, plus 41 putative substrates predicted on the basis of ‘omic’ and biochemical data. In particular, it was demonstrated that new classes of substrates, such as halogenated compounds, sulfur compounds or aromatics, enable methanogenesis. In this article, which straddles the boundary between a scientific paper and a review, we take stock of all these known and putative substrates, and calculate Gibbs free energy changes under standard biological conditions for methanogenesis. Out of all the substrates for methanogenesis, two-thirds of the ΔGr0′ values calculated lie between 0 and –30 kJ mol−1 CH4. We discuss the sources of these substrates, the environments in which they occur and the taxa that use them to produce energy through methanogenesis. Given the diversity of anoxic environments in which these different substrates are found, methanogens could populate a greater number of ecological niches than previously thought.

Gerald E. Marsh

Modern developments in nonequilibrium thermodynamics have significant implications for the origins of life. The reasons for this are closely related to a generalized version of the second law of thermodynamics recently found for entropy production during irreversible evolution of a given system such as self-replicating RNA. This paper is intended to serve as an introduction to these developments.

Jinfei Chai

Based on the basic principle of thermodynamics, an elastoplastic damage constitutive model of concrete is constructed in this paper. The model is realized and verified in FLAC3D, which provides a solid foundation for the study of dynamic response and fatigue damage to the base structure of a heavy haul railway tunnel. The dynamic response and damage distribution of the base structure of a heavy-duty railway tunnel with defects were numerically simulated by the concrete elastic-plastic damage constitutive model. Then, by analyzing the response characteristics of the tunnel basement structure under different surrounding rock softening degrees, different foundation suspension range and different foundation structure damage degree are determined. The results show the following: (1) The elastoplastic damage constitutive model of concrete can well describe the stress–strain relationship of materials, especially with the simulation results of post peak softening being in good agreement with the test results, and the simulation effect of the unloading–reloading process of the cyclic loading and unloading test also meet the requirements. (2) The initial stress field and dynamic response of the tunnel basement structure under the action of train vibration load are very different from the ideal state of the structure design when the surrounding rock of the base is softened, the base is suspended, or the basement structure is damaged. With the surrounding rock softening, basement hanging, or basement structure damage developing to a certain extent, the basement structure will be damaged. (3) The horizontal dynamic stress amplitude increases with the increase in the softening degree of the basement surrounding rock. The horizontal dynamic stress of the measuring point increases with the increase in the width of the hanging out area when the hanging out area is located directly below the loading line. When the degree of damage to the basement structure is aggravated, the horizontal dynamic tensile stress of each measuring point gradually decreases. (4) The maximum principal stress increment increases with the increase in the fracture degree of the basement structure, while the minimum principal stress increment decreases with the increase in the fracture degree of the basement structure, but the variation range of the large and minimum principal stress increments is small. The research results have important theoretical and practical significance for further analysis of the damage mechanism and control technology of the foundation structure of a heavy haul railway tunnel with defects.

S. V. Bobyr

The phase transformations in alloyed iron-carbon alloys is largely related to diffusion of components, foremost to the carbon. For the analysis of diffusive processes in alloy steels, it is possible to use the mathematical methods of non-equilibrium thermodynamics. The equation for the diffusive fluxes of the system contains unknown in general case of coefficients activity of elements and vacancies, and their derivatives for to the concentrations, that extraordinarily makes it difficult being of values of cross coefficients. In the article a non-equilibrium thermodynamics methodology of calculation of diffusive fluxes at presence of two phases in alloy steels is described. It allows one to calculate both direct- and cross coefficients in the Onsager equations. Formulas for calculation of thermodynamics forces in the alloy steel – for iron, alloying element of substitution – chrome, of element of introduction – carbon and vacancies, are presented. Common expressions are suggested for calculation of cross-factors, motive forces and fluxes in the Onsager’s equations for a multicomponent thermodynamic system. The example of using the developed model to find changes in concentrations and diffusion fluxes over time is given. For the model system used, it was established that at the stage of predominant diffusion of carbon in the alloy steel, cementite inclusions with a size of about 18 nm are formed rather quickly (within ~ 200 s). The technique developed in the article allows one to perform diffusion kinetics calculations in multicomponent thermodynamic systems, which are also iron-carbon alloys and to control the size of the phases formed, for example, of carbide nanoparticles.

Chunkan Yu, U. Maas

In order to address the impact of the concentration gradients on the chemistry – turbulence interaction in turbulent flames, the REDIM reduced chemistry is constructed incorporating the scalar dissipation rate, which is a key quantity describing the turbulent mixing process. This is achieved by providing a variable gradient estimate in the REDIM evolution equation. In such case, the REDIM reduced chemistry is tabulated as a function of the reduced coordinates and the scalar dissipation rate as an additional progress variable. The constructed REDIM is based on a detailed transport model including the differential diffusion, and is validated for a piloted non-premixed turbulent jet flames (Sandia Flame D and E). The results show that the newly generated REDIM can reproduce the thermo-kinetic quantities very well, and the differential molecular diffusion effect can also be well captured.