Hasil untuk "Thermodynamics"

Yu Liu, Ya-Juan Liu

W. Israel, J. Stewart

D. R. Stull, E. Westrum, G. C. Sinke

T. L. Hill, J. Gillis

H. Helgeson

A. Shapiro

U. F. Kocks

W. G. McMillan, J. Mayer

R. Kosloff

Quantum thermodynamics addresses the emergence of thermodynamic laws from quantum mechanics. The viewpoint advocated is based on the intimate connection of quantum thermodynamics with the theory of open quantum systems. Quantum mechanics inserts dynamics into thermodynamics, giving a sound foundation to finite-time-thermodynamics. The emergence of the 0-law, I-law, II-law and III-law of thermodynamics from quantum considerations is presented. The emphasis is on consistency between the two theories, which address the same subject from different foundations. We claim that inconsistency is the result of faulty analysis, pointing to flaws in approximations.

F. Brandão, M. Horodecki, N. Ng et al.

Significance In ordinary thermodynamics, transitions are governed by a single quantity–the free energy. Its monotonicity is a formulation of the second law. Here, we find that the second law for microscopic or highly correlated systems takes on a very different form than it does at the macroscopic scale, imposing not just one constraint on state transformations, but many. We find a family of quantum free energies which generalize the standard free energy, and can never increase. The ordinary second law corresponds to the nonincreasing of one of these free energies, with the remainder imposing additional constraints on thermodynamic transitions. In the thermodynamic limit, these additional second laws become equivalent to the standard one. We also prove a strengthened version of the zeroth law of thermodynamics, allowing a definition of temperature. The second law of thermodynamics places constraints on state transformations. It applies to systems composed of many particles, however, we are seeing that one can formulate laws of thermodynamics when only a small number of particles are interacting with a heat bath. Is there a second law of thermodynamics in this regime? Here, we find that for processes which are approximately cyclic, the second law for microscopic systems takes on a different form compared to the macroscopic scale, imposing not just one constraint on state transformations, but an entire family of constraints. We find a family of free energies which generalize the traditional one, and show that they can never increase. The ordinary second law relates to one of these, with the remainder imposing additional constraints on thermodynamic transitions. We find three regimes which determine which family of second laws govern state transitions, depending on how cyclic the process is. In one regime one can cause an apparent violation of the usual second law, through a process of embezzling work from a large system which remains arbitrarily close to its original state. These second laws are relevant for small systems, and also apply to individual macroscopic systems interacting via long-range interactions. By making precise the definition of thermal operations, the laws of thermodynamics are unified in this framework, with the first law defining the class of operations, the zeroth law emerging as an equivalence relation between thermal states, and the remaining laws being monotonicity of our generalized free energies.

Yawen Wang, Jiating He, Cuicui Liu et al.

M. Lostaglio, K. Korzekwa, D. Jennings et al.

Quantum mechanics and thermodynamics are fundamental fields of physics. Scientists show how the processing of quantum coherence is constrained by the laws of thermodynamics.

Md Manirul Ali, Po-Wen Chen

Understanding thermodynamics far from equilibrium at the quantum scale remains a fundamental challenge, particularly in the presence of quantum coherence. Here we develop a first-principles framework for nonequilibrium quantum thermodynamics by integrating quantum resource theory of coherence with thermodynamic laws. We derive a previously unexplored entropy balance relation that explicitly separates entropy flux due to heat exchange from entropy production arising from the loss of quantum coherence. This formulation identifies the appropriate thermodynamic entropy in nonequilibrium quantum processes as the energy entropy associated with energy measurements, demonstrating that the von Neumann entropy does not, in general, represent thermodynamic entropy away from equilibrium. Within this framework, dynamical temperature, free energy, work, and heat are consistently defined, and both the first and second laws are shown to hold far from equilibrium. Applying the theory to an exactly solvable open quantum system, we reveal how equilibrium thermodynamics emerges dynamically in the weak-coupling limit. Our results establish a unified and operational foundation for nonequilibrium quantum thermodynamics and clarify the fundamental thermodynamic role of quantum coherence.

Jin-Fu Chen

We develop a Lindblad framework for quantum stochastic thermodynamics to study the nonequilibrium thermodynamics of open quantum systems. Our approach adopts the local quantum detailed balance condition, ensuring thermodynamic consistency and leading to a joint fluctuation theorem of quantum work and heat. Instead of solving the full evolution of the density matrix, we employ an effective parametrization to derive the full counting statistics of work and heat and determine the optimal protocols. As an application, we refine the quantum Brownian motion master equation to ensure the quantum detailed balance condition, derive the optimal protocols at different temperatures, and study the work statistics. Our framework provides fundamental insights and practical strategies for optimizing thermodynamic processes in open quantum systems.

Mehdi Kabir, Corey Field, David Howe

To date, two-phase flow boiling has been extensively investigated for various working fluids and geometries, mainly under operating pressures and mass fluxes in the range of medium to high. However, very limited studies have been conducted, focusing on low-pressure low-flow (LPLF) conditions. Given insufficient experimental data available in the literature, most of the existing empirical correlations fail to properly predict boiling heat transfer coefficients (BHTCs) in LPLF conditions, highlighting the need for further experimental investigations. The present study experimentally investigates the heat transfer performance of single-phase and two-phase flow boiling of distilled water in a horizontal conventional tube at constant wall heat flux under LPLF conditions where the operating pressure is set to be subatmospheric and the mass flux ranges below 20 kg/m²-s. For the saturated flow boiling, the effects of mass flux and local vapor quality on the local BHTCs and Nusselt were evaluated, revealing that local BHTCs reach a peak at a certain range of vapor qualities between 55% and 75%, while increasing with the mass flux. It was also found that the impact of mass flux is stronger than that of vapor quality on the local BHTCs. The experimental results in the present study were then compared with several well-known empirical BHTC correlations in the literature to identify those with least deviations under the LPLF conditions. In contrast to single-phase flow, heat loss estimation and vapor quality measurement are known as one of the main error sources in characterizing heat transfer coefficients for two-phase flow boiling. Accordingly, the present study employs two approaches, in parallel, to reliably estimate heat losses, calibrate heat supplies, and measure local vapor qualities under the operating conditions investigated.

Lamia Benahmed, Khaled Aliane, Brahim Rostane et al.

<p>This work focuses on geothermal energy recovery using a vertical geothermal heat exchanger coupled with a heat pump for heating applications. The primary objective of this study is to conduct a 3D numerical simulation to evaluate the effects of baffles on the thermal performance of a U-shaped heat exchanger. These baffles, designed to alter flow characteristics, were implemented to enhance heat transfer and optimize overall system efficiency. The mathematical model is based on the governing equations of fluid mechanics and thermodynamics, solved using the finite volume method in the Ansys CFX software. Various baffle configurations were investigated, focusing on their placement (on the inlet and outlet tube), geometry, and the use of perforations with decreasing diameters. Simulations were conducted for a Reynolds number of Re=3600, capturing the flow behavior under specific conditions. The analysis revealed that the optimal configuration, involving baffles strategically placed on the outlet tube with decreasing perforation diameters, significantly improved thermal performance. These findings highlight the potential for designing more efficient heat exchangers in geothermal systems, paving the way for advancements in sustainable energy solutions.</p>

Volker Dreißigacker

The successful establishment of battery electric vehicles (BEVs) is strongly linked to criteria such as cost and range. In particular, the need for air conditioning strains battery capacities and limits the availability of BEVs. Thermal energy storage systems (TESs) open up alternative paths for heat and cold supply with excellent scalability and cost efficiency. Previous TES concepts have largely focused on heat during cold seasons, but storage-based air conditioning systems for all seasons are still missing. To fill this gap, a concept based on a Brayton cycle allowing heat and cold supply and, simultaneously, an output of electrical energy at times when no air conditioning is needed was investigated. Central thermal components include water-based cold storage and electrically heated, high-temperature, solid-medium storage, both with innovative TPMS structures and flexible operation managements. With transient simulation studies a system was identified with effective storage densities of up to 100 Wh/kg, reaching a constant heat and cold supply of 5 kW and 2.5 kW, respectively, over 41 min. In addition, the underlying cycle allows an electrical output of up to 1.7 kW during times of inactive air conditioning requirements. Compared to a reference system designed only for winter operation, the moderately lower storage densities are compensated by proportionately longer discharging times. By combining a compact and dynamic Brayton cycle with a TES in BEVs, a storage-based air conditioning system with high utilization potential and high operational flexibility was developed. In addition to further optimizations, the knowledge for TES solutions can also be transferred to today’s air conditioning systems, extending the solution space for storage-supported thermomanagement options in BEVs.

Samriti Vaid, Sanyog Sharma, Varinder Kaur et al.

The purpose of our work was to increase the efficacy of jute fibers through the application of two successive treatments: sodium hydroxide (NaOH) and cetyltrimethylammonium bromide (CTAB). The goal was to remove the dye Novacron Red FN-2BL from wastewater. We thoroughly investigated how different parameters, such as initial concentration of dye (20–100 mg/L), adsorbent dosage (0.01 g–0.10 g), contact time (2–16 min), pH (from 2 to12) and temperature (298, 308, and 318 K) affected the kinetics of removal of dye. The removal efficiency of reactive dye Novacron Red FN-2BL by the jute treated with surfactant CTAB (JST) adsorbent peaked at 95% using 0.05 g/50 mL dye solution, an initial concentration of dye of 40 mg/L, pH 7, contact time of 8 min, and temperature of 298 K. A thorough understanding of the process of adsorption was made possible by our experimental setup, and the data fit effectively into a variety of isothermal and kinetic models. In particular, the adsorption behavior was well-represented by the Langmuir isotherm model, and the adsorption kinetics followed a pseudo-second-order model. Notably, a remarkable 74.63 mg/g of monolayer adsorption was possible at 318 K. An endothermic adsorption phenomenon is reflected by the increasing value of KF (Freundlich’s constant) on rising temperature. Furthermore, the Dubinin–Radushkevich isotherm demonstrated a physisorption-like mechanism for the adsorption of Novacron red FN-2BL dye on JST; the magnitude of E, which varied from 1.29 to 2.24 KJ/mol when the temperature rose from 298 to 318 K, indicated the process’s temperature dependence. With respect to thermodynamics, the ΔH∗ value was found to be 11.73 KJ/mol, and the ΔS∗ value was determined as 65.74 J/mol/K. An entropy-driven nature, spontaneity, and feasibility of Novacron Red FN-2BL adsorption on JST are highlighted by the positive ΔS∗ and consistently negative ΔG∗ (ranging from −7.87 KJ/mol to −9.19 KJ/mol, across all temperatures).

Yanqin Chen, Donghui Wang, Xueli Wang et al.

Abstract To enhance the performance of biochar made from almond shells for adsorption of phenol pollutants in water, we prepared an almond shell-based biochar and modified it through combined pyrolysis with KOH and EDTA-4Na at 750 °C, yielding almond shell-based modified activated carbon (A-BC); the mass ratio of biochar, EDTA-4Na, and KOH was 1:1:3. A-BC was characterized by using Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, the Brunauer–Emmett–Teller method, and X-ray Diffraction. The adsorption conditions of A-BC for phenol were optimized through single-factor experiments, and the adsorption mechanism was explored through kinetics and thermodynamics assays. The results show that A-BC exhibits a honeycomb-like structure with a specific surface area of 1050 m2 g−1 and a micropore ratio of 86%. A-BC is rich in functional groups (-OH, -CH2, N–C, C-H, N–H) closely related to phenol adsorption. The adsorption of phenol by A-BC is a spontaneous exothermic process involving both physical adsorption and chemical adsorption (including hydrogen bonding and π-π interactions). The pseudo-second-order kinetic model adequately describes the adsorption process, which consists of liquid film diffusion, surface adsorption, and intraparticle diffusion stages. At 25 °C, with an A-BC dosage of 1.0 g L−1, initial phenol concentration of 400 mg L−1, and contact time of 60 min, A-BC exhibited significant adsorption capacities of 161 and 149 mg g−1 for simulated water and phenol-containing wastewater from coal chemical industries, respectively. A-BC demonstrated good reuse performance and strong adsorption capacity for phenol, indicating its potential application in treating phenol-containing wastewater from coal chemical industries.

Frank Weinhold

We address the scientific “time” concept in the context of more general relaxation processes toward the <i>Wärmetod</i> of thermodynamic equilibrium. More specifically, we sketch a construction of a conceptual ladder of chemical reaction steps that can rigorously bridge a description from the microscopic domain of molecular quantum chemistry to the macroscopic materials domain of Gibbsian thermodynamics. This conceptual reformulation follows the pioneering work of Kenichi Fukui (Nobel 1981) in rigorously formulating the <i>intrinsic reaction coordinate</i> (IRC) pathway for controlled description of non-equilibrium passages between reactant and product equilibrium states of an overall material transformation. Elementary <i>chemical reaction steps</i> are thereby identified as the logical building-blocks of an integrated mathematical framework that seamlessly spans the gulf between classical (pre-1925) and quantal (post-1925) scientific conceptions and encompasses both static and dynamic aspects of material change. All modern chemical reaction rate studies build on the apparent infallibility of quantum-chemical solutions of Schrödinger’s wave equation and its Dirac-type relativistic corrections. This infallibility may now be properly accepted as an added“inductive law” of Gibbsian chemical thermodynamics, the only component of 19th-century physics that passed <i>intact</i> through the revolutionary quantum upheavals of 1925.