The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform

Koji Okuda - One of the best experts on this subject based on the ideXlab platform.

  • compatibility of Carnot efficiency with finite power in an underdamped brownian Carnot Cycle in small temperature difference regime
    arXiv: Statistical Mechanics, 2020
    Co-Authors: Kosuke Miura, Yuki Izumida, Koji Okuda
    Abstract:

    We study the possibility of achieving the Carnot efficiency in a finite-power Brownian Carnot Cycle described by the underdamped Langevin equation in the small temperature-difference regime. A previous study [V. Holubec and A. Ryabov, Phys. Rev. Lett. {\bf 121}, 120601 (2018)] pointed out that it is possible to achieve both the Carnot efficiency and finite power in an overdamped Brownian Carnot Cycle by considering the vanishing limit of the relaxation times of the system. However, an overlooked heat leakage exists at the beginning of the isothermal processes because of the instantaneous adiabatic processes when considering the overdamped limit in an underdamped Brownian Carnot Cycle. As heat leakage decreases efficiency, the compatibility of the Carnot efficiency and finite power should be reexamined. We study the relaxation-times dependence of the efficiency and power in the underdamped Brownian Carnot Cycle in the small temperature-difference regime where the heat leakage can be neglected. Additionally, we demonstrate that the compatibility of the Carnot efficiency and finite power is achieved by considering the vanishing limit of the relaxation times of the system. Furthermore, we show that this result is consistent with a trade-off relation between power and efficiency by explicitly deriving the relation of our Cycle in terms of the relaxation times.

  • Molecular kinetic analysis of a local equilibrium Carnot Cycle.
    Physical Review E, 2017
    Co-Authors: Yuki Izumida, Koji Okuda
    Abstract:

    We identify a velocity distribution function of ideal gas particles that is compatible with the local equilibrium assumption and the fundamental thermodynamic relation satisfying the endoreversibility. We find that this distribution is a Maxwell-Boltzmann distribution with a spatially uniform temperature and a spatially varying local center-of-mass velocity. We construct the local equilibrium Carnot Cycle of an ideal gas, based on this distribution, and show that the efficiency of the present Cycle is given by the endoreversible Carnot efficiency using the molecular kinetic temperatures of the gas. We also obtain an analytic expression of the efficiency at maximum power of our Cycle under a small temperature difference. Our theory is also confirmed by a molecular dynamics simulation.

  • Onsager coefficients of a Brownian Carnot Cycle
    The European Physical Journal B, 2010
    Co-Authors: Yuki Izumida, Koji Okuda
    Abstract:

    We study a Brownian Carnot Cycle introduced by Schmiedl and Seifert [Europhys. Lett. 81, 20003 (2008)] from a viewpoint of the linear irreversible thermodynamics. By considering the entropy production rate of this Cycle, we can determine thermodynamic forces and fluxes of the Cycle and calculate the Onsager coefficients for general protocols, that is, arbitrary schedules to change the potential confining the Brownian particle. We show that these Onsager coefficients contain the information of the protocol shape and they satisfy the tight-coupling condition irrespective of whatever protocol shape we choose. These properties may give an explanation why the Curzon-Ahlborn efficiency often appears in the finite-time heat engines.

  • onsager coefficients of a brownian Carnot Cycle
    arXiv: Statistical Mechanics, 2010
    Co-Authors: Yuki Izumida, Koji Okuda
    Abstract:

    We study a Brownian Carnot Cycle introduced by T. Schmiedl and U. Seifert [Europhys. Lett. \textbf{81}, 20003 (2008)] from a viewpoint of the linear irreversible thermodynamics. By considering the entropy production rate of this Cycle, we can determine thermodynamic forces and fluxes of the Cycle and calculate the Onsager coefficients for general protocols, that is, arbitrary schedules to change the potential confining the Brownian particle. We show that these Onsager coefficients contain the information of the protocol shape and they satisfy the tight-coupling condition irrespective of whatever protocol shape we choose. These properties may give an explanation why the Curzon-Ahlborn efficiency often appears in the finite-time heat engines.

  • Onsager coefficients of a finite-time Carnot Cycle.
    Physical review. E Statistical nonlinear and soft matter physics, 2009
    Co-Authors: Yuki Izumida, Koji Okuda
    Abstract:

    We study a finite-time Carnot Cycle of a weakly interacting gas which we can regard as a nearly ideal gas in the limit of T(h)-T(c) --> 0 where T(h) and T(c) are the temperatures of the hot and cold heat reservoirs, respectively. In this limit, we can assume that the Cycle is working in the linear-response regime and can calculate the Onsager coefficients of this Cycle analytically using the elementary molecular kinetic theory. We reveal that these Onsager coefficients satisfy the so-called tight-coupling condition and this fact explains why the efficiency at the maximal power eta(max) of this Cycle can attain the Curzon-Ahlborn efficiency from the viewpoint of the linear-response theory.

Pierre Neveu - One of the best experts on this subject based on the ideXlab platform.

  • Equivalent Carnot Cycle concept applied to a thermochemical solid/gas resorption system
    Applied Thermal Engineering, 1998
    Co-Authors: Jean Castaing-lasvignottes, Pierre Neveu
    Abstract:

    Abstract Recent work on second law analysis performed on sorption systems has led to the equivalent Carnot Cycle concept. Such a tool is very powerful in obtaining rapid and clear analysis of the energy degradation occurring in solid/gas refrigerators. It explains and quantifies the difference between Carnot's coefficient of performance ( COP ) associated with the three heat reservoir temperatures and the actual COP in terms of entropy productions. It also points out that the equivalent Carnot Cycle for the sorption process is not a classical three-temperature Carnot Cycle. In fact, the energy exchanged between the absorption/desorption process and the evaporation/condensation process is not mechanical work but takes the form of Δ H − T Δ S . This analysis is performed here for the solid/gas resorption system, involving two reactors, one driving the Cycle, the other devoted to cold production. Such a development is depicted through combined first and second law analysis and illustrated on ( T , Q / T ) diagrams built previously for solid/gas equilibrium. The equivalent Carnot Cycle shows that, in this case, avoiding gas exchange between the two sub-systems allows exchange of mechanical work, leading to higher values of COP .

  • equivalent Carnot Cycle concept applied to a thermochemical solid gas resorption system
    Applied Thermal Engineering, 1998
    Co-Authors: Jean Castainglasvignottes, Pierre Neveu
    Abstract:

    Abstract Recent work on second law analysis performed on sorption systems has led to the equivalent Carnot Cycle concept. Such a tool is very powerful in obtaining rapid and clear analysis of the energy degradation occurring in solid/gas refrigerators. It explains and quantifies the difference between Carnot's coefficient of performance ( COP ) associated with the three heat reservoir temperatures and the actual COP in terms of entropy productions. It also points out that the equivalent Carnot Cycle for the sorption process is not a classical three-temperature Carnot Cycle. In fact, the energy exchanged between the absorption/desorption process and the evaporation/condensation process is not mechanical work but takes the form of Δ H − T Δ S . This analysis is performed here for the solid/gas resorption system, involving two reactors, one driving the Cycle, the other devoted to cold production. Such a development is depicted through combined first and second law analysis and illustrated on ( T , Q / T ) diagrams built previously for solid/gas equilibrium. The equivalent Carnot Cycle shows that, in this case, avoiding gas exchange between the two sub-systems allows exchange of mechanical work, leading to higher values of COP .

Yuki Izumida - One of the best experts on this subject based on the ideXlab platform.

  • compatibility of Carnot efficiency with finite power in an underdamped brownian Carnot Cycle in small temperature difference regime
    arXiv: Statistical Mechanics, 2020
    Co-Authors: Kosuke Miura, Yuki Izumida, Koji Okuda
    Abstract:

    We study the possibility of achieving the Carnot efficiency in a finite-power Brownian Carnot Cycle described by the underdamped Langevin equation in the small temperature-difference regime. A previous study [V. Holubec and A. Ryabov, Phys. Rev. Lett. {\bf 121}, 120601 (2018)] pointed out that it is possible to achieve both the Carnot efficiency and finite power in an overdamped Brownian Carnot Cycle by considering the vanishing limit of the relaxation times of the system. However, an overlooked heat leakage exists at the beginning of the isothermal processes because of the instantaneous adiabatic processes when considering the overdamped limit in an underdamped Brownian Carnot Cycle. As heat leakage decreases efficiency, the compatibility of the Carnot efficiency and finite power should be reexamined. We study the relaxation-times dependence of the efficiency and power in the underdamped Brownian Carnot Cycle in the small temperature-difference regime where the heat leakage can be neglected. Additionally, we demonstrate that the compatibility of the Carnot efficiency and finite power is achieved by considering the vanishing limit of the relaxation times of the system. Furthermore, we show that this result is consistent with a trade-off relation between power and efficiency by explicitly deriving the relation of our Cycle in terms of the relaxation times.

  • Molecular kinetic analysis of a local equilibrium Carnot Cycle.
    Physical Review E, 2017
    Co-Authors: Yuki Izumida, Koji Okuda
    Abstract:

    We identify a velocity distribution function of ideal gas particles that is compatible with the local equilibrium assumption and the fundamental thermodynamic relation satisfying the endoreversibility. We find that this distribution is a Maxwell-Boltzmann distribution with a spatially uniform temperature and a spatially varying local center-of-mass velocity. We construct the local equilibrium Carnot Cycle of an ideal gas, based on this distribution, and show that the efficiency of the present Cycle is given by the endoreversible Carnot efficiency using the molecular kinetic temperatures of the gas. We also obtain an analytic expression of the efficiency at maximum power of our Cycle under a small temperature difference. Our theory is also confirmed by a molecular dynamics simulation.

  • Onsager coefficients of a Brownian Carnot Cycle
    The European Physical Journal B, 2010
    Co-Authors: Yuki Izumida, Koji Okuda
    Abstract:

    We study a Brownian Carnot Cycle introduced by Schmiedl and Seifert [Europhys. Lett. 81, 20003 (2008)] from a viewpoint of the linear irreversible thermodynamics. By considering the entropy production rate of this Cycle, we can determine thermodynamic forces and fluxes of the Cycle and calculate the Onsager coefficients for general protocols, that is, arbitrary schedules to change the potential confining the Brownian particle. We show that these Onsager coefficients contain the information of the protocol shape and they satisfy the tight-coupling condition irrespective of whatever protocol shape we choose. These properties may give an explanation why the Curzon-Ahlborn efficiency often appears in the finite-time heat engines.

  • onsager coefficients of a brownian Carnot Cycle
    arXiv: Statistical Mechanics, 2010
    Co-Authors: Yuki Izumida, Koji Okuda
    Abstract:

    We study a Brownian Carnot Cycle introduced by T. Schmiedl and U. Seifert [Europhys. Lett. \textbf{81}, 20003 (2008)] from a viewpoint of the linear irreversible thermodynamics. By considering the entropy production rate of this Cycle, we can determine thermodynamic forces and fluxes of the Cycle and calculate the Onsager coefficients for general protocols, that is, arbitrary schedules to change the potential confining the Brownian particle. We show that these Onsager coefficients contain the information of the protocol shape and they satisfy the tight-coupling condition irrespective of whatever protocol shape we choose. These properties may give an explanation why the Curzon-Ahlborn efficiency often appears in the finite-time heat engines.

  • Onsager coefficients of a finite-time Carnot Cycle.
    Physical review. E Statistical nonlinear and soft matter physics, 2009
    Co-Authors: Yuki Izumida, Koji Okuda
    Abstract:

    We study a finite-time Carnot Cycle of a weakly interacting gas which we can regard as a nearly ideal gas in the limit of T(h)-T(c) --> 0 where T(h) and T(c) are the temperatures of the hot and cold heat reservoirs, respectively. In this limit, we can assume that the Cycle is working in the linear-response regime and can calculate the Onsager coefficients of this Cycle analytically using the elementary molecular kinetic theory. We reveal that these Onsager coefficients satisfy the so-called tight-coupling condition and this fact explains why the efficiency at the maximal power eta(max) of this Cycle can attain the Curzon-Ahlborn efficiency from the viewpoint of the linear-response theory.

Alex J. Decaria - One of the best experts on this subject based on the ideXlab platform.

  • the Carnot Cycle and area specific work equivalence on a skew t logp diagram
    Monthly Weather Review, 2008
    Co-Authors: Alex J. Decaria
    Abstract:

    Abstract Attempts to calculate the area to specific work equivalence on a skew T–logp diagram for a Carnot Cycle can lead to large errors if the pressures of the nodes of the Cycle are estimated from the diagram. The cause is the extreme sensitivity of the calculation to the pressures of the nodes. To keep errors within 10%, the pressures of the nodes must be known to within 0.1 hPa, a precision that is not practical by direct reading from the diagram. To avoid these errors the pressures of the nodes should be calculated directly from Poisson’s equation, which relates temperature, potential temperature, and pressure.

  • The Carnot Cycle and Area-Specific Work Equivalence on a Skew T–logp Diagram
    Monthly Weather Review, 2008
    Co-Authors: Alex J. Decaria
    Abstract:

    Abstract Attempts to calculate the area to specific work equivalence on a skew T–logp diagram for a Carnot Cycle can lead to large errors if the pressures of the nodes of the Cycle are estimated from the diagram. The cause is the extreme sensitivity of the calculation to the pressures of the nodes. To keep errors within 10%, the pressures of the nodes must be known to within 0.1 hPa, a precision that is not practical by direct reading from the diagram. To avoid these errors the pressures of the nodes should be calculated directly from Poisson’s equation, which relates temperature, potential temperature, and pressure.

Ferdi Altintas - One of the best experts on this subject based on the ideXlab platform.

  • Construction of a quantum Carnot heat engine Cycle
    Quantum Information Processing, 2020
    Co-Authors: Selçuk Çakmak, Mustafa Çandır, Ferdi Altintas
    Abstract:

    The microscopic state description of an irreversible quantum Carnot Cycle for a general quantum working medium is investigated. An efficiency lag term, which quantifies the deviation of the irreversible Cycle efficiency from the classical Carnot efficiency, is given in terms of the total entropy increase in the universe. The efficiency lag and the total entropy increase in the universe are directly connected to the quantum relative entropy between the density matrices obtained at the end of the quantum adiabatic and the relaxation steps of the Cycle. The total entropy increase and the efficiency lag are found to be always nonnegative quantities. Our results give a direct proof that the irreversible Cycle efficiency is always smaller than the classical Carnot efficiency. Two interacting spins under an external magnetic field are proposed as the working medium of the irreversible quantum Carnot Cycle. The external magnetic field is considered to be quasistatically changed during the steps of the Cycle. The coupling between the spins is found to break down the scale invariance and make the quantum Carnot Cycle irreversible. It is shown that while the quantum coupling can lower the Cycle efficiency monotonically to zero, it can make the irreversible Cycle to produce more work than the one obtained from the uncoupled spins. The conditions in which one can always construct a reversible Carnot Cycle for the coupled spin working medium are also given.

  • Quantum Carnot Cycle with inner friction
    Quantum Information Processing, 2020
    Co-Authors: Selçuk Çakmak, Ferdi Altintas
    Abstract:

    A single driven spin is investigated as the working substance of a six-stroke irreversible quantum Carnot Cycle. The role of inner friction associated with the finite-time adiabatic transformations on the Cycle efficiency and the harvested work are investigated in detail. The inner friction is found to significantly reduce the work output and the Cycle efficiency which can make the engine incapable to produce positive work for the too fast adiabatic transformations. The ideal Carnot efficiency is found to be reached only for the quasistatic transformations. A deviation of the Cycle efficiency from the classical Carnot efficiency has been given by an efficiency lag which is directly related to the total entropy production due to the inner friction. The released heat in the relaxation processes of the Cycle is associated with the entropy production and the inner friction. The extension of the results for a scale-invariant quantum working substance and the possible experimental implementation of the irreversible quantum Carnot Cycle in a liquid-state nuclear magnetic resonance setup are also discussed.

  • quantum Carnot Cycle with inner friction
    arXiv: Quantum Physics, 2020
    Co-Authors: Selçuk Çakmak, Ferdi Altintas
    Abstract:

    A single driven spin is investigated as the working substance of a six-stroke irreversible quantum Carnot Cycle. The role of inner friction associated with the finite-time adiabatic transformations on the Cycle efficiency and the harvested work are investigated in detail. The inner friction is found to significantly reduce the work output and the Cycle efficiency which can make the engine incapable to produce positive work for the too fast adiabatic transformations. The ideal Carnot efficiency is found to be reached only for the quasi-static transformations. A deviation of the Cycle efficiency from the classical Carnot efficiency has been given by an efficiency lag which is directly related to the total entropy production due to the inner friction. The released heat in the relaxation processes of the Cycle are associated with the entropy production and the inner friction. The extension of the results for a scale invariant quantum working substance and the possible experimental implementation of the irreversible quantum Carnot Cycle in a liquid state nuclear magnetic resonance setup are also discussed.