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## A Precise Formulation of the Third Law of Thermodynamics

Fonte: SPRINGER
Publicador: SPRINGER

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

45.89%

#Thermodynamics#Third law#Entropy#Adiabatic accessibility#Black holes#GROUND-STATE#DENSITY#SYSTEMS#ENTROPY#ENERGY#Physics, Mathematical

The third law of thermodynamics is formulated precisely: all points of the state space of zero temperature I""(0) are physically adiabatically inaccessible from the state space of a simple system. In addition to implying the unattainability of absolute zero in finite time (or ""by a finite number of operations""), it admits as corollary, under a continuity assumption, that all points of I""(0) are adiabatically equivalent. We argue that the third law is universally valid for all macroscopic systems which obey the laws of quantum mechanics and/or quantum field theory. We also briefly discuss why a precise formulation of the third law for black holes remains an open problem.; CNPq; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP ( Brazil)

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## Finite-time thermodynamics: Engine performance improved by optimized piston motion

Fonte: PubMed
Publicador: PubMed

Tipo: Artigo de Revista Científica

Publicado em /04/1981
EN

Relevância na Pesquisa

65.9%

The methods of finite-time thermodynamics are used to find the optimal time path of an Otto cycle with friction and heat leakage. Optimality is defined by maximization of the work per cycle; the system is constrained to operate at a fixed frequency, so the maximum power is obtained. The result is an improvement of about 10% in the effectiveness (second-law efficiency) of a conventional near-sinusoidal engine.

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## Optimal paths for minimizing lost available work during heat transfer processes with a generalized heat transfer law

Fonte: Sociedade Brasileira de Física
Publicador: Sociedade Brasileira de Física

Tipo: Artigo de Revista Científica
Formato: text/html

Publicado em 01/03/2009
EN

Relevância na Pesquisa

55.76%

#Finite time thermodynamics#Lost available work#Optimal control#Heat transfer process#Heat transfer law

A common of finite-time heat transfer processes between high- and low-temperature sides with a generalized heat transfer law [q ∝ (Δ(Tn ))m] are studied in this paper. The optimal heating and cooling configurations for minimizing lost available work are derived for the fixed initial and final temperatures of the working fluid of the system (low-temperature side). Optimal paths are compared with the common strategies of constant heat flux, constant source (reservoir) temperature and the minimum entropy generation operation by numerical examples. The condition corresponding to the minimum lost available work strategy is that corresponding to a constant rate of lost available work, not only valid for Newton's heat transfer law [q ∝ ΔT] but also valid for the generalized convective heat transfer law [q ∝ (ΔT)m ]. The obtained results are more general and can provide some theoretical guidelines for the designs and operations of practical heat exchangers.

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## Finite-time thermodynamics of port-Hamiltonian systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 06/08/2013

Relevância na Pesquisa

55.97%

#Condensed Matter - Statistical Mechanics#Mathematics - Dynamical Systems#Mathematics - Optimization and Control

In this paper, we identify a class of time-varying port-Hamiltonian systems
that is suitable for studying problems at the intersection of statistical
mechanics and control of physical systems. Those port-Hamiltonian systems are
able to modify their internal structure as well as their interconnection with
the environment over time. The framework allows us to prove the First and
Second laws of thermodynamics, but also lets us apply results from optimal and
stochastic control theory to physical systems. In particular, we show how to
use linear control theory to optimally extract work from a single heat source
over a finite time interval in the manner of Maxwell's demon. Furthermore, the
optimal controller is a time-varying port-Hamiltonian system, which can be
physically implemented as a variable linear capacitor and transformer. We also
use the theory to design a heat engine operating between two heat sources in
finite-time Carnot-like cycles of maximum power, and we compare those two heat
engines.; Comment: To appear in Physica D (accepted July 2013)

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## Reconstruction of $f(T)$ gravity: Rip cosmology, finite-time future singularities and thermodynamics

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

46.07%

We demonstrate that there appear finite-time future singularities in $f(T)$
gravity with $T$ being the torsion scalar. We reconstruct a model of $f(T)$
gravity with realizing the finite-time future singularities. In addition, it is
explicitly shown that a power-low type correction term $T^\beta$ ($\beta>1$)
such as a $T^2$ term can remove the finite-time future singularities in $f(T)$
gravity. Moreover, we study $f(T)$ models with realizing inflation in the early
universe, the $\Lambda$CDM model, Little Rip cosmology and Pseudo-Rip
cosmology. It is demonstrated that the disintegration of bound structures for
Little Rip and Pseudo-Rip cosmologies occurs in the same way as in gravity with
corresponding dark energy fluid. We also discuss that the time-dependent matter
instability in the star collapse can occur in $f(T)$ gravity. Furthermore, we
explore thermodynamics in $f(T)$ gravity and illustrate that the second law of
thermodynamics can be satisfied around the finite-time future singularities for
the universe with the temperature inside the horizon being the same as that of
the apparent horizon.; Comment: 38 pages, no figure, version accepted for publication in Physical
Review D

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## Near-equilibrium universality and bounds on efficiency in quasi-static regime with finite source and sink

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

45.87%

We show the validity of some results of finite-time thermodynamics, also
within the quasi-static framework of classical thermodynamics. First, we
consider the efficiency at maximum work (EMW) from finite source and sink
modelled as identical thermodynamic systems. The near-equilibrium regime is
characterized by expanding the internal energy upto second order (i.e. upto
linear response) in the difference of initial entropies of the source and the
sink. It is shown that the efficiency is given by a universal expression $2
\eta_C / (4-\eta_C)$, where $\eta_C$ is the Carnot efficiency. Then, different
sizes of source and sink are treated, by combining different numbers of copies
of the same thermodynamic system. The efficiency of this process is found to be
${\boldsymbol\eta}_0 = \eta_C/ (2-\gamma \eta_C)$, where the parameter $\gamma$
depends only on the relative size of the source and the sink. This implies that
within the linear response theory, EMW is bounded as ${\eta_C}/{2} \le
{{\boldsymbol\eta}}_0 \le {\eta_C}/{(2 - \eta_C)}$, where the upper (lower)
bound is obtained with a sink much larger (smaller) in size than the source. We
also remark on the behavior of the efficiency beyond linear response.; Comment: 11 pages, no figures. New discussion added on universality beyond
linear response

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## Weighted reciprocal of temperature, weighted thermal flux, and their applications in finite-time thermodynamics

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

65.94%

The concepts of weighted reciprocal of temperature and weighted thermal flux
are proposed for a heat engine operating between two heat baths and outputting
mechanical work. With the aid of these two concepts, the generalized
thermodynamic fluxes and forces can be expressed in a consistent way within the
framework of irreversible thermodynamics. Then the efficiency at maximum power
output for a heat engine, one of key topics in finite-time thermodynamics, is
investigated on the basis of a generic model under the tight-coupling
condition. The corresponding results have the same forms as those of
low-dissipation heat engines [M. Esposito, R. Kawai, K. Lindenberg, and C. Van
den Broeck, {Phys. Rev. Lett.} \textbf{105}, 150603 (2010)]. The mappings from
two kinds of typical heat engines, such as the low-dissipation heat engine and
the Feynman ratchet, into the present generic model are constructed. The
universal efficiency at maximum power output up to the quadratic order is found
to be valid for a heat engine coupled symmetrically and tightly with two baths.
The concepts of weighted reciprocal of temperature and weighted thermal flux
are also transplanted to the optimization of refrigerators.; Comment: 13 journal pages, 2 figures

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## Quantum Thermodynamics

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 10/05/2013

Relevância na Pesquisa

45.9%

Quantum thermodynamics addresses the emergence of thermodynamical laws from
quantum mechanics. The link 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
consistence 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.

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## Finite time thermodynamics for a single level quantum dot

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 21/09/2009

Relevância na Pesquisa

65.94%

We investigate the finite time thermodynamics of a single-level fermion
system interacting with a thermal reservoir through a tunneling junction. The
optimal protocol to extract the maximum work from the system when moving the
single energy level between an initial higher value and a final lower value in
a finite time is calculated from a quantum master equation. The calculation
also yields the optimal protocol to raise the energy level with the expenditure
of the least amount of work on the system. The optimal protocol displays
discontinuous jumps at the initial and final times.; Comment: 7 pages, 5 figures

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## Thermodynamic optimization of a Penrose process: an engineers' approach to black hole thermodynamics

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 20/11/2015

Relevância na Pesquisa

46.04%

#General Relativity and Quantum Cosmology#Astrophysics - High Energy Astrophysical Phenomena#Condensed Matter - Statistical Mechanics

In this work we present a new view on the thermodynamics of black holes
introducing effects of irreversibility by employing thermodynamic optimization
and finite-time thermodynamics. These questions are of importance both in
physics and in engineering, combining standard thermodynamics with optimal
control theory in order to find optimal protocols and bounds for realistic
processes without assuming anything about the microphysics involved. We find
general bounds on the maximum work and the efficiency of thermodynamic
processes involving black holes that can be derived exclusively from the
knowledge of thermodynamic relations at equilibrium. Since these new bounds
consider the finite duration of the processes, they are more realistic and
stringent than their reversible counterparts. To illustrate our arguments, we
consider in detail the thermodynamic optimization of a Penrose process, i.e.
the problem of finding the least dissipative process extracting all the angular
momentum from a Kerr black hole in finite time. We discuss the relevance of our
results for real astrophysical phenomena, for the comparison with laboratory
black holes analogues and for other theoretical aspects of black hole
thermodynamics.; Comment: 12 pages, 4 figures. Comments are welcome!

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## Continuity and boundary conditions in thermodynamics: From Carnot's efficiency to efficiencies at maximum power

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

46.06%

[...] By the beginning of the 20th century, the principles of thermodynamics
were summarized into the so-called four laws, which were, as it turns out,
definitive negative answers to the doomed quests for perpetual motion machines.
As a matter of fact, one result of Sadi Carnot's work was precisely that the
heat-to-work conversion process is fundamentally limited; as such, it is
considered as a first version of the second law of thermodynamics. Although it
was derived from Carnot's unrealistic model, the upper bound on the
thermodynamic conversion efficiency, known as the Carnot efficiency, became a
paradigm as the next target after the failure of the perpetual motion ideal. In
the 1950's, Jacques Yvon published a conference paper containing the necessary
ingredients for a new class of models, and even a formula, not so different
from that of Carnot's efficiency, which later would become the new efficiency
reference. Yvon's first analysis [...] went fairly unnoticed for twenty years,
until Frank Curzon and Boye Ahlborn published their pedagogical paper about the
effect of finite heat transfer on output power limitation and their derivation
of the efficiency at maximum power, now known as the Curzon-Ahlborn (CA)
efficiency. The notion of finite rate explicitly introduced time in
thermodynamics...

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## Optimal ratios of the piston speeds for a finite speed endoreversible Carnot heat engine cycle

Fonte: Sociedad Mexicana de Física
Publicador: Sociedad Mexicana de Física

Tipo: Artigo de Revista Científica
Formato: text/html

Publicado em 01/04/2010
EN

Relevância na Pesquisa

75.99%

#Finite time thermodynamics#endoreversible Carnot heat engine#finite speed of the piston#finite rate of heat transfer#power#efficiency

The performance of an endoreversible Carnot heat engine cycle is analyzed and optimized using the theory of finite time thermodynamics based on Agrawal and Menon's i model of finite speed of the piston on the four branches and Curzon and Ahlborn's ii model of finite rate of heat transfer. The finite speeds of the piston on the four branches are further assumed to be different, which is unlike the model of constant-speed of the piston on the four branches. The analytical formula between power and efficiency of the cycle is derived for a fixed cycle period. There exist optimal ratios of the finite piston speeds on the four branches. The effects of the temperature ratio of the heat reservoirs on the dimensionless power versus efficiency of the cycle and isothermal expansion ratio are obtained by numerical examples.

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## Maximum efficiency of an irreversible heat engine with a distributed working fluid and linear phenomenological heat transfer law

Fonte: Sociedad Mexicana de Física
Publicador: Sociedad Mexicana de Física

Tipo: Artigo de Revista Científica
Formato: text/html

Publicado em 01/06/2010
EN

Relevância na Pesquisa

65.87%

#Finite-time thermodynamics#linear phenomenological heat transfer law#heat engine#distributed working fluid#maximum efficiency#optimal control

Maximum efficiency of an irreversible heat engine with a distributed working fluid, in which the heat transfers between the working fluid and the heat reservoirs obey the linear phenomenological heat transfer law , is studied in this paper by using finite-time thermodynamics based on Orlov and Berry's work i. Two kinds of efficiencies are defined, and the problems are divided into three cases. Optimal control theory is used to determine the upper bounds of efficiencies of the heat engines for various cases. Numerical examples of the two efficiencies for the irreversible heat engine with lumped-parameter model working between variable temperature reservoirs are provided, and the effects of changes of the reservoir's temperature on the maximum efficiency of the heat engine are analyzed. The obtained results are also compared with those obtained by Orlov and Berry ii with Newtonian heat transfer law .

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## Finite-time exergy with a finite heat reservoir and generalized radiative heat transfer law

Fonte: Sociedad Mexicana de Física
Publicador: Sociedad Mexicana de Física

Tipo: Artigo de Revista Científica
Formato: text/html

Publicado em 01/08/2010
EN

Relevância na Pesquisa

75.95%

#Finite time thermodynamics#finite-time exergy#finite heat reservoir#generalized radiative heat transfer law#optimal control

The problem of the maximum work that can be extracted from a system consisting of one finite heat reservoir and one subsystem with the generalized radiative heat transfer law [q ∞ Δ (Tn)] is investigated in this paper. Finite-time exergy is derived for a fixed duration and a given initial state of the subsystem by applying optimal control theory. The optimal subsystem temperature configuration for the finite-time exergy consists of three segments, including the initial and final instantaneous adiabatic branches and the intermediate heat transfer branch. Analyses for special examples show that the optimal configuration of the heat transfer branch with Newton's heat transfer law [q ∞ Δ (T)] is that the temperatures of the reservoir and the subsystem change exponentially with time and the temperature ratio between them is a constant; The optimal configuration of the heat transfer branch with the linear phenomenological heat transfer law [q ∞ Δ (T-1)] is such that the temperatures of the reservoir and the subsystem change linearly and non-linearly with time, respectively, and the difference in reciprocal temperature between them is a constant. The optimal configuration of the heat transfer branch with the radiative heat transfer law [q ∞ Δ (T4)] is significantly different from those with the former two different heat transfer laws. Numerical examples are given...

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## Exergoeconomic performance optimization for an endoreversible regenerative gas turbine closed-cycle cogeneration plant

Fonte: Sociedad Mexicana de Física
Publicador: Sociedad Mexicana de Física

Tipo: Artigo de Revista Científica
Formato: text/html

Publicado em 01/06/2009
EN

Relevância na Pesquisa

55.76%

#Finite time thermodynamics#gas turbine cycle cogeneration plant#exergoeconomic performance#profit rate

Finite time exergoeconomic performance of an endoreversible regenerative gas turbine closed-cycle cogeneration plant coupled to constant temperature heat reservoirs is investigated. The analytical formulae about profit rate and exergy efficiency of the cogeneration plant with the heat resistance losses in the hot-, cold- and consumer-side heat exchangers and the regenerator are deduced, respectively. By means of numerical calculations, the heat conductance allocation among the four heat exchangers and pressure ratio of the compressor are optimized by taking the maximum profit rate as the objective. The characteristic of optimal dimensionless profit rate versus corresponding exergy efficiency is investigated and the effects of design parameters on optimal performance of the cogeneration plant are also analyzed. The results show that there exist a sole group of optimal heat conductance allocations among the four heat exchangers and an optimal pressure ratio of the compressor which lead to the maximum dimensionless profit rate, and there exists an optimal consumer-side temperature which leads to double-maximum dimensionless profit rate.

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## Finite-time thermoeconomic optimization of a non endoreversible heat engine model

Fonte: Sociedad Mexicana de Física
Publicador: Sociedad Mexicana de Física

Tipo: Artigo de Revista Científica
Formato: text/html

Publicado em 01/06/2009
EN

Relevância na Pesquisa

55.76%

Within the context of Finite-Time Thermodynamics (FTT), we study the thermoeconomics of a simplified non-endoreversible thermal power plant model (the so-called Novikov engine). In our study, we use different heat transfer laws: the so called Newton's law of cooling, the Stefan-Boltzmann radiation law, the Dulong-Petit's law and another phenomenological heat transfer law. We use two FTT optimization criteria: the maximum power regime (MP) and the so-named modified ecological criterion for performance analysis. This last criterion leads the engine model towards a mode of performance that appreciably diminishes the engine's wasted energy. It is shown that under ecological conditions the plant dramatically reduces the amount of heat rejected to the environment, and a loss of profit is translated into a better usage of fuel such that the heat rejected towards the environment is remarkably reduced compared to that of a maximum power regime. Besides, we analyze the effect on the reduction of power output and the optimal efficiencies in terms of an internal irreversibility parameter that comes from the Clausius inequality which characterizes the degree of internal irreversibility.

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## Effect of heat transfer on the performance of a thermoelectric heat pump driven by a thermoelectric generator

Fonte: Sociedad Mexicana de Física
Publicador: Sociedad Mexicana de Física

Tipo: Artigo de Revista Científica
Formato: text/html

Publicado em 01/08/2009
EN

Relevância na Pesquisa

65.97%

#Combined thermoelectric device#thermoelectric generator#thermoelectric heat pump#heat transfer#finite-time thermodynamics#non-equilibrium thermodynamics

A model of a thermoelectric heat pump driven by a thermoelectric generator with external heat transfer irreversibility is proposed. The performance of the combined thermoelectric heat pump device obeying Newton's heat transfer law is analyzed using the combination of finite time thermodynamics and non-equilibrium thermodynamics. Two analytical formulae for heating load versus working electrical current, and the coefficient of performance (COP) versus working electrical current, are derived. For a fixed total heat transfer surface area of four heat exchangers, the allocations of the heat transfer surface area among the four heat exchangers are optimized for maximizing the heating load and the COP of the combined thermoelectric heat pump device. For a fixed total number of thermoelectric elements, the ratio of the number of thermoelectric elements of the generator to the total number of thermoelectric elements is also optimized for maximizing both the heating load and the COP of the combined thermoelectric heat pump device. The influences of thermoelectric element allocation and heat transfer area allocation are analyzed by detailed numerical examples. The optimum working electrical currents for maximum heating load and maximum COP at different total numbers of thermoelectric elements and different total heat transfer areas are provided...

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## Heating load, COP, exergy loss rate, exergy output rate and ecological optimizations for a class of generalized irreversible universal heat pump cycles

Fonte: Sociedad Mexicana de Física
Publicador: Sociedad Mexicana de Física

Tipo: Artigo de Revista Científica
Formato: text/html

Publicado em 01/08/2010
EN

Relevância na Pesquisa

65.87%

#Finite time thermodynamics#irreversible universal heat pump cycle#heating load#COP#exergy loss rate#exergy output rate#ecological function

The optimal performance of a class of generalized irreversible universal steady flow heat pump cycle model, which consists of two heat-absorbing branches, two heat-releasing branches and two irreversible adiabatic branches with the losses of heat-resistance, heat leakage and internal irreversibility is analyzed by using finite time thermodynamics. The analytical formulae about heating load, coefficient of performance (COP), exergy loss rate, exergy output rate and ecological function of the universal heat pump cycle are derived. Moreover, performance comparisons among maximum COP condition, a given exergy output rate condition and maximum ecological function condition are carried out by using numerical examples. It is shown that the ecological function objective is an excellent candidate objective with the ideal of an ecological and long-term goal. The effects of heat leakage and internal irreversibility on the cycle performance are discussed. The universal cycle model gives a unified description of seven heat pump cycles, and the results obtained include the performance characteristics of Brayton, Otto, Diesel, Atkinson, Dual, Miller and Carnot heat pump cycles with the losses of heat-resistance, heat leakage and internal irreversibility.

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## On the optimum operation conditions of an endoreversible heat engine with different heat transfer laws in the thermal couplings

Fonte: Sociedad Mexicana de Física
Publicador: Sociedad Mexicana de Física

Tipo: Artigo de Revista Científica
Formato: text/html

Publicado em 01/08/2008
EN

Relevância na Pesquisa

65.87%

Within the context of Finite-Time Thermodynamics (FTT) we study the optimum operating conditions of an endoreversible engine model. In this model we consider different heat transfer modes from the hot reservoir to the working fluid, while the mode of heat transfer from the working fluid to the cold reservoir is governed by a Newtonian heat transfer law. In our analysis we use two modes of performance, the maximum power regimen and the so-called ecological function. We calculate the optimum temperatures of the working fluid and the optimum efficiency in terms of the relevant system parameters. We show how the efficiency under a maximum ecological function is greater than the maximum efficiency under maximum power conditions.

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## Optimization of an irreversible Carnot engine in finite time and finite size

Fonte: Sociedad Mexicana de Física
Publicador: Sociedad Mexicana de Física

Tipo: Artigo de Revista Científica
Formato: text/html

Publicado em 01/08/2006
EN

Relevância na Pesquisa

65.93%

In this work, we consider the class of irreversible Carnot engines that results from combining the characteristics of two models found in the literature: the model in finite time and the model in finite size. The performance of the resulting model, including three irreversibilities, was doubly-optimized in finite time and finite size. The first optimization of power and efficiency, maintaining the thermal conductances fixed, was performed in finite time. Since the optimum time ratio from the first optimization, is the same for both maximum power and maximum efficiency, this means that the model can be newly optimized but now in finite size. Then, the second optimization, maintaining the overall heat transfer coefficient constant, was performed. For both optimizations, analytical expressions for the efficiency that maximizes the power and maximum efficiency were obtained. Changing the order in which partial optimizations were carried out, a remarkable optimal property was obtained: the resources of total contact time and the total area of heat transfer are proportional.

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