The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform

Jincan Chen - One of the best experts on this subject based on the ideXlab platform.

  • Ecological optimisation of an irreversible Stirling Heat Engine
    International Journal of Ambient Energy, 2001
    Co-Authors: Jincan Chen
    Abstract:

    SYNOPSIS A general cycle model of an irreversible Stirling Heat Engine using an ideal or Van der Waals gas as the working substance is established. It includes three main sources of the irreversibility such as the Heat transfer across finite-temperature differences in the isothermal processes, the regenerative loss resulting from the non-perfect regeneration in the regenerator, and the Heat leak loss between the external Heat reservoirs. The ecological function is taken as an objective function for optimisation. The performance characteristics of the Stirling Heat Engine at maximum ecological function are revealed. They are compared with other performance characteristics of the Stirling Heat Engine at maximum power output and efficiency in order to expound the significance of the ecological objective function. The results obtained here are of importance in the optimal design and operation of real Stirling Heat Engines. Finally, it is pointed out that the results obtained in this paper are very general, fr...

  • maximum specific power output of an irreversible radiant Heat Engine
    Energy Conversion and Management, 1996
    Co-Authors: Jincan Chen, R L Kiang
    Abstract:

    With the help of an irreversible Carnot cycle model with continuous flow, the effects of the irreversibility of finite rate Heat transfer and internal irreversibility of the working fluid on the performance of a radiant Heat Engine are studied. The specific power output of the Heat Engine is chosen to be an objective function for Heat Engine optimization. The maximum specific power output and the corresponding efficiency are derived. The optimal problems concerning the primary performance parameters of the Heat Engine, such as the efficiency, temperatures of the working fluid and Heat transfer areas are discussed in detail.

  • the maximum power output and maximum efficiency of an irreversible carnot Heat Engine
    Journal of Physics D, 1994
    Co-Authors: Jincan Chen
    Abstract:

    The effect of thermal resistance, Heat leakage and internal irreversibility resulting from the working fluid on the performance of a Carnot Heat Engine is investigated using a new cyclic model. The power output and efficiency of the Heat Engine are adopted as objective functions for Heat Engine optimization. The optimal performance of the Heat Engine is analysed systematically. Some significant results are obtained. For example, the maximum power output and maximum efficiency are determined. The efficiency of the Heat Engine at maximum power output and the power output of the Heat Engine at maximum efficiency are also calculated. Curves of the power output varying with the efficiency of the Heat Engine are obtained. These curves can indicate clearly the rational regions of efficiency and power output for an irreversible Carnot Heat Engine. It is pointed out that all the conclusions concerning a reversible Carnot Heat Engine, an endoreversible Carnot Heat Engine only affected by thermal resistance and an irreversible Carnot Heat Engine with internal irreversibility and/or Heat leakage can be deduced from the results in this paper.

  • Optimization of a solar‐driven Heat Engine
    Journal of Applied Physics, 1992
    Co-Authors: Jincan Chen
    Abstract:

    The optimum performance of the solar‐driven Heat Engine consisting of a solar collector and a Heat Engine is investigated, based on the linear Heat‐loss model of solar collectors and the endoreversible Carnot cycle model of Heat Engines. Some new results such as the optimum operating temperature of the solar collector, the maximum overall efficiency of the system, the optimum operating temperatures of the working fluid in two isothermal Heat exchange processes of the Heat Engine, and so on, are derived. It is expounded that these results have more realistic meaning than the previous relative theoretics for the optimum design of practical solar‐driven Heat Engine systems.

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

  • Coupled quantum Otto Heat Engine and refrigerator with inner friction
    Quantum Information Processing, 2019
    Co-Authors: Deniz Türkpençe, Ferdi Altintas
    Abstract:

    We investigate two coupled spins 1/2 in a magnetic field as the working substance of the quantum Otto cycle. In the quantum adiabatic strokes, finite-time parametric transformations are employed either in the coupling strength or in the magnetic field. The operation regimes, where the mode of the cycle is a refrigerator or a Heat Engine, are explored. The role of the total allocated time to the quantum adiabatic stages on the performance of the quantum Otto refrigerator and the Heat Engine is investigated in detail. The finite-time adiabatic transformations are found to increase the Shannon entropy which is quantum in origin. The effect known as the inner friction is found to negatively effect the performances of the quantum Heat Engine and the refrigerator. The strong frictional losses are also found to induce inactive operation regimes where the mode of the cycle is neither a refrigerator nor a Heat Engine.

Francesco Giazotto - One of the best experts on this subject based on the ideXlab platform.

  • Efficient and tunable Aharonov-Bohm quantum Heat Engine
    Physical Review B, 2019
    Co-Authors: Géraldine Haack, Francesco Giazotto
    Abstract:

    We propose a quantum Heat Engine based on an Aharonov-Bohm interferometer in a two-terminal geometry, and investigate its thermoelectric performances in the linear response regime. Sizeable thermopower (up to $\sim 0.3\,\text{mV}$/K) as well as $ZT$ values largely exceeding unity can be achieved for suitable system parameters and temperature bias across the interferometer leading to thermal efficiency at maximum power approaching $30\%$ of the Carnot limit. This is close to the optimal efficiency at maximum power achievable for a two-terminal Heat Engine. Changing either the magnetic flux or a bias voltage through a capacitively-coupled electrode allow to finely tune the quantum Heat Engine performance. Despite the simplicity of the setup, the high performances of the Engine are stable over a wide range of temperatures and length imbalances, promising towards experimental realization.

  • Josephson Quantum Heat Engine
    Physical Review Applied, 2016
    Co-Authors: Giampiero Marchegiani, Francesco Giazotto, Pauli Virtanen, Michele Campisi
    Abstract:

    The design of a mesoscopic self-oscillating Heat Engine that works thanks to purely quantum effects is presented. The proposed scheme is amenable to experimental implementation with current state-of-the-art nanotechnology and materials. One of the main features of the structure is its versatility: The Engine can deliver work to a generic load without galvanic contact. This makes it a promising building block for low-temperature on-chip energy management applications. The Heat Engine consists of a circuit featuring a thermoelectric element based on a ferromagnetic insulator-superconductor tunnel junction and a Josephson weak link that realizes a purely quantum DC/AC converter. This enables contactless transfer of work to the load (a generic RL circuit). The performance of the Heat Engine is investigated as a function of the thermal gradient applied to the thermoelectric junction. Power up to $1$ pW can be delivered to a load $R_L=10\ \Omega$.

Rosario Fazio - One of the best experts on this subject based on the ideXlab platform.

  • Thermoelectric properties of an interacting quantum dot based Heat Engine
    Physical Review B, 2017
    Co-Authors: Paolo Andrea Erdman, Francesco Mazza, Riccardo Bosisio, Giuliano Benenti, Rosario Fazio, Fabio Taddei
    Abstract:

    We study the thermoelectric properties and Heat-to-work conversion performance of an interacting, multilevel quantum dot (QD) weakly coupled to electronic reservoirs. We focus on the sequential tunneling regime. The dynamics of the charge in the QD is studied by means of master equations for the probabilities of occupation. From here we compute the charge and Heat currents in the linear response regime. Assuming a generic multiterminal setup, and for low temperatures (quantum limit), we obtain analytical expressions for the transport coefficients which account for the interplay between interactions (charging energy) and level quantization. In the case of systems with two and three terminals we derive formulas for the power factor $Q$ and the figure of merit $ZT$ for a QD-based Heat Engine, identifying optimal working conditions which maximize output power and efficiency of Heat-to-work conversion. Beyond the linear response we concentrate on the two-terminal setup. We first study the thermoelectric nonlinear coefficients assessing the consequences of large temperature and voltage biases, focusing on the breakdown of the Onsager reciprocal relation between thermopower and Peltier coefficient. We then investigate the conditions which optimize the performance of a Heat Engine, finding that in the quantum limit output power and efficiency at maximum power can almost be simultaneously maximized by choosing appropriate values of electrochemical potential and bias voltage. At last we study how energy level degeneracy can increase the output power.

  • the power of a critical Heat Engine
    Nature Communications, 2016
    Co-Authors: Michele Campisi, Rosario Fazio
    Abstract:

    Since its inception about two centuries ago thermodynamics has sparkled continuous interest and fundamental questions. According to the second law no Heat Engine can have an efficiency larger than Carnot’s efficiency. The latter can be achieved by the Carnot Engine, which however ideally operates in infinite time, hence delivers null power. A currently open question is whether the Carnot efficiency can be achieved at finite power. Most of the previous works addressed this question within the Onsager matrix formalism of linear response theory. Here we pursue a different route based on finite-size-scaling theory. We focus on quantum Otto Engines and show that when the working substance is at the verge of a second order phase transition diverging energy fluctuations can enable approaching the Carnot point without sacrificing power. The rate of such approach is dictated by the critical indices, thus showing the universal character of our analysis. The second law of thermodynamics says that the efficiency of a Heat Engine is limited by the Carnot efficiency. Here, the authors use finite-size-scaling theory to investigate whether this ultimate limit can be achieved at finite power using quantum Otto Engines.

Ronnie Kosloff - One of the best experts on this subject based on the ideXlab platform.

  • irreversible performance of a quantum harmonic Heat Engine
    New Journal of Physics, 2006
    Co-Authors: Yair Rezek, Ronnie Kosloff
    Abstract:

    The unavoidable irreversible loss of power in a Heat Engine is found to be of quantum origin. Following thermodynamic tradition, a model quantum Heat Engine operating in an Otto cycle is analysed, where the working medium is composed of an ensemble of harmonic oscillators and changes in volume correspond to changes in the curvature of the potential well. Equations of motion for quantum observables are derived for the complete cycle of operation. These observables are sufficient to determine the state of the system and with it all thermodynamical variables. Once the external controls are set, the Engine settles to a limit cycle. Conditions for optimal work, power and entropy production are derived. At high temperatures and quasistatic operating conditions, the efficiency at maximum power coincides with the endoreversible result . The optimal compression ratio varies from in the quasistatic limit where the irreversibility is dominated by Heat conductance to in the sudden limit when the irreversibility is dominated by friction. When the Engine deviates from adiabatic conditions, the performance is subject to friction. The origin of this friction can be traced to the noncommutability of the kinetic and potential energy of the working medium.

  • irreversible performance of a quantum harmonic Heat Engine
    arXiv: Quantum Physics, 2006
    Co-Authors: Yair Rezek, Ronnie Kosloff
    Abstract:

    The unavoidable irreversible losses of power in a Heat Engine are found to be of quantum origin. Following thermodynamic tradition a model quantum Heat Engine operating by the Otto cycle is analyzed. The working medium of the model is composed of an ensemble of harmonic oscillators. A link is established between the quantum observables and thermodynamical variables based on the concept of canonical invariance. These quantum variables are sufficient to determine the state of the system and with it all thermodynamical variables. Conditions for optimal work, power and entropy production show that maximum power is a compromise between the quasistatic limit of adiabatic following on the compression and expansion branches and a sudden limit of very short time allocation to these branches. At high temperatures and quasistatic operating conditions the efficiency at maximum power coincides with the endoreversible result. The optimal compression ratio varies from the square root of the temperature ratio in the quasistatic limit where their reversibility is dominated by Heat conductance to the temperature ratio to the power of 1/4 in the sudden limit when the irreversibility is dominated by friction. When the Engine deviates from adiabatic conditions the performance is subject to friction. The origin of this friction can be traced to the noncommutability of the kinetic and potential energy of the working medium.