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Fengrui Sun - One of the best experts on this subject based on the ideXlab platform.

  • Local stability of a non-endoreversible Carnot Refrigerator working at the maximum ecological function
    Applied Mathematical Modelling, 2014
    Co-Authors: Lingen Chen, Fengrui Sun
    Abstract:

    Abstract Local stability of a non-endoreversible Carnot Refrigerator at the maximum ecological function is studied with Newton’s heat transfer law between working fluid and heat reservoirs. The steady state of the Refrigerator working at the maximum ecological function is steady. It is derived that a general expression of relaxation time described as stability of the system refers to heat capacity C , total heat exchange area F , temperature ratio of heat reservoirs τ , the degree of internal irreversibility ϕ , heat transfer coefficients α and β . Distributing information of phase portraits of system is obtained. The results can provide some theoretical guidelines for the designs of practical Refrigerator.

  • Ecological optimisation of irreversible harmonic oscillator Carnot Refrigerator
    Journal of the Energy Institute, 2013
    Co-Authors: Lei-da Chen, Xiong Liu, Fengrui Sun
    Abstract:

    AbstractA model of a quantum harmonic oscillator Carnot Refrigerator with heat resistance, internal irreversibility and heat leakage is established in this paper. Based on the quantum master equation and semigroup approach, equations of some important performance parameters, such as cooling load, coefficient of performance (COP), exergy output rate, entropy generation rate and ecological function (a criterion E = A/τ−T0σ representing the optimal compromise between exergy output rate A/τ and exergy loss rate T0σ), for the irreversible quantum Carnot Refrigerator are derived. The optimal ecological performance of the Refrigerator at high temperature limit is analysed using numerical examples. The effects of internal irreversibility and heat leakage on the optimal ecological performance are discussed. Performance comparisons of the quantum Refrigerator under maximum ecological function, maximum COP and maximum cooling load conditions are also performed. Some special cases, i.e. endoreversible, frictionless a...

  • Ecological optimization of a generalized irreversible Carnot Refrigerator in the case of Q∝ (Δ T n ) m
    International Journal of Sustainable Energy, 2012
    Co-Authors: Lingen Chen, Fengrui Sun
    Abstract:

    The optimal exergy-based ecological performance of a generalized irreversible Carnot Refrigerator with losses of heat resistance, heat leakage and internal irreversibility is derived by taking an ecological optimization criterion as the objective. The transfer between the working fluid and heat reservoirs obeys a generalized heat transfer law Q∝ Δ (T n ) m . Some special examples are discussed. Results include the optimal ecological performance of the irreversible Carnot Refrigerator with various heat transfer laws, which were obtained in many studies, and can provide some theoretical guidelines for the design of practical Refrigerators.

  • Optimal piston speed ratio analyses for irreversible Carnot Refrigerator and heat pump using finite time thermodynamics, finite speed thermodynamics and direct method
    Journal of the Energy Institute, 2011
    Co-Authors: Lei-da Chen, Huijun Feng, Fengrui Sun
    Abstract:

    AbstractAn irreversible Carnot refrigeration and heat pump cycle model with external irreversibilities caused by finite rate of heat transfer, heat leakage from heat sink to heat source and internal irreversibilities caused by finite piston speed, friction and gas throttling is established by using the combination of finite time thermodynamics, finite speed thermodynamics and direct method. Different from the model of constant speed of the piston on the four branches, the piston speeds on the four branches in this model are assumed to be unequal. Expressions of cooling load and coefficient of performance (COP) of the Carnot refrigeration cycle as well as heating load and COP of the heat pump cycle are derived for a fixed cycle period. Numerical examples show that the curves of COP versus cooling load and COP versus heating load are parabolic like ones, and there exist optimal finite piston speed ratios on the four branches, which lead to the maximum COPs. Moreover, the effects of the heat leakage coeffici...

  • Ecological performance of an endoreversible Carnot Refrigerator with complex heat transfer law
    International Journal of Ambient Energy, 2011
    Co-Authors: Lingen Chen, Fengrui Sun
    Abstract:

    The optimal ecological objective of an endoreversible Carnot Refrigerator based on a new generalised heat transfer law , including generalised convective heat transfer law and generalised radiative heat transfer law, is derived. The ecological objective function representing the best compromise between the exergy output rate and exergy loss rate (entropy production rate) of the Refrigerator. The results include the optimal ecological performance of the endoreversible Carnot Refrigerator with various heat transfer laws, which obtained in many literatures.

J. M. M. Roco - One of the best experts on this subject based on the ideXlab platform.

  • coefficient of performance under optimized figure of merit in minimally nonlinear irreversible Refrigerator
    EPL, 2013
    Co-Authors: Yuki Izumida, Calvo A Hernandez, Koji Okuda, J. M. M. Roco
    Abstract:

    We apply the model of minimally nonlinear irreversible heat engines developed by Izumida and Okuda (EPL, 97 (2012) 10004) to Refrigerators. The model assumes extended Onsager relations including a new nonlinear term accounting for dissipation effects. The bounds for the optimized regime under an appropriate figure of merit and the tight-coupling condition are analyzed and successfully compared with those obtained previously for low-dissipation Carnot Refrigerators in the finite-time thermodynamics framework. Besides, we study the bounds for the nontight-coupling case numerically. We also introduce a leaky low-dissipation Carnot Refrigerator and show that it serves as an example of the minimally nonlinear irreversible Refrigerator, by calculating its Onsager coefficients explicitly.

  • Irreversible Refrigerators under per-unit-time coefficient of performance optimization
    Applied Physics Letters, 1997
    Co-Authors: Santiago Velasco, J. M. M. Roco, Alejandro Medina, A. Calvo Hernández
    Abstract:

    A finite-time thermodynamics analysis is used to investigate the optimal coefficient of performance (COP) of an irreversible Carnot Refrigerator using the per-unit-time COP as an objective function for optimization. The model includes finite-rate heat transfers between the refrigerant and the external heat reservoirs, heat leak between heat reservoirs, and internal dissipations of the refrigerant. Heat conductances associated with heat transfers are optimized by maximizing the cooling power per unit of capital invested in the Refrigerator. The obtained results are consistent with performance data for real low-temperature Refrigerators.

  • New Performance Bounds for a Finite-Time Carnot Refrigerator
    Physical Review Letters, 1997
    Co-Authors: Santiago Velasco, J. M. M. Roco, Alejandro Medina, A. Calvo Hernández
    Abstract:

    An upper bound for the coefficient of performance (COP) of endoreversible Refrigerators which depends only on the ratio {tau}=T{sub c}/T{sub h} between the cold and hot reservoir temperatures has been elusive to date. We address here this long standing problem by analyzing an endoreversible Carnot Refrigerator that operates in conditions of maximum per-unit-time COP. Two novel results are obtained: (1) A long sought {tau}-dependent upper bound for the COP of Refrigerators. (2) A {tau}-dependent optimum distribution of the heat conductances associated with the coupling between the refrigerant and the heat reservoirs. Moreover, when the method is applied to heat engines, the resulting optimum efficiency is even closer to real efficiencies than the well-known Curzon-Ahlborn result. {copyright} {ital 1997} {ital The American Physical Society}

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

  • coefficient of performance under optimized figure of merit in minimally nonlinear irreversible Refrigerator
    EPL, 2013
    Co-Authors: Yuki Izumida, Calvo A Hernandez, Koji Okuda, J. M. M. Roco
    Abstract:

    We apply the model of minimally nonlinear irreversible heat engines developed by Izumida and Okuda (EPL, 97 (2012) 10004) to Refrigerators. The model assumes extended Onsager relations including a new nonlinear term accounting for dissipation effects. The bounds for the optimized regime under an appropriate figure of merit and the tight-coupling condition are analyzed and successfully compared with those obtained previously for low-dissipation Carnot Refrigerators in the finite-time thermodynamics framework. Besides, we study the bounds for the nontight-coupling case numerically. We also introduce a leaky low-dissipation Carnot Refrigerator and show that it serves as an example of the minimally nonlinear irreversible Refrigerator, by calculating its Onsager coefficients explicitly.

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

  • Local stability of a non-endoreversible Carnot Refrigerator working at the maximum ecological function
    Applied Mathematical Modelling, 2014
    Co-Authors: Lingen Chen, Fengrui Sun
    Abstract:

    Abstract Local stability of a non-endoreversible Carnot Refrigerator at the maximum ecological function is studied with Newton’s heat transfer law between working fluid and heat reservoirs. The steady state of the Refrigerator working at the maximum ecological function is steady. It is derived that a general expression of relaxation time described as stability of the system refers to heat capacity C , total heat exchange area F , temperature ratio of heat reservoirs τ , the degree of internal irreversibility ϕ , heat transfer coefficients α and β . Distributing information of phase portraits of system is obtained. The results can provide some theoretical guidelines for the designs of practical Refrigerator.

  • Ecological optimization of a generalized irreversible Carnot Refrigerator in the case of Q∝ (Δ T n ) m
    International Journal of Sustainable Energy, 2012
    Co-Authors: Lingen Chen, Fengrui Sun
    Abstract:

    The optimal exergy-based ecological performance of a generalized irreversible Carnot Refrigerator with losses of heat resistance, heat leakage and internal irreversibility is derived by taking an ecological optimization criterion as the objective. The transfer between the working fluid and heat reservoirs obeys a generalized heat transfer law Q∝ Δ (T n ) m . Some special examples are discussed. Results include the optimal ecological performance of the irreversible Carnot Refrigerator with various heat transfer laws, which were obtained in many studies, and can provide some theoretical guidelines for the design of practical Refrigerators.

  • Exergoeconomic performance of an endoreversible Carnot Refrigerator with complex heat transfer law
    International journal of ambient energy, 2011
    Co-Authors: Lingen Chen, Jun Li, Chih Wu
    Abstract:

    The finite-time exergoeconomic performance of an endoreversible Carnot refrigeration with a complex heat transfer law, including generalised convective and radiative heat transfer laws, , is investigated in this article. The focus of this article is to obtain the compromised optimisation between economics (profit) and the energy utilisation factor (coefficient of performance, COP) for the endoreversible Carnot Refrigerator, by searching the optimum COP at maximum profit, which is termed as the finite-time exergoeconomic performance bound. The obtained results include those obtained in many literatures and can provide some theoretical guidance for the design of practical Refrigerators.

  • Ecological performance of an endoreversible Carnot Refrigerator with complex heat transfer law
    International Journal of Ambient Energy, 2011
    Co-Authors: Lingen Chen, Fengrui Sun
    Abstract:

    The optimal ecological objective of an endoreversible Carnot Refrigerator based on a new generalised heat transfer law , including generalised convective heat transfer law and generalised radiative heat transfer law, is derived. The ecological objective function representing the best compromise between the exergy output rate and exergy loss rate (entropy production rate) of the Refrigerator. The results include the optimal ecological performance of the endoreversible Carnot Refrigerator with various heat transfer laws, which obtained in many literatures.

  • Cooling load and co-efficient of performance optimizations for a generalized irreversible Carnot Refrigerator with heat transfer law q ∞ (ΔTn)m:
    Proceedings of the Institution of Mechanical Engineers Part E: Journal of Process Mechanical Engineering, 2008
    Co-Authors: Lingen Chen, Fengrui Sun
    Abstract:

    AbstractThe fundamental optimal relation between cooling load and coefficient of performance (COP) of a generalized irreversible Carnot Refrigerator is derived based on a new generalized heat transfer law, including generalized convective heat transfer law and generalized radiative heat transfer law, q ∞ (ΔTn)m. The generalized irreversible Carnot Refrigerator model incorporates several internal and external irreversibilities, such as heat resistance, bypass heat leakage, friction, turbulence, and other undesirable irreversibility factors. The added irreversibilities besides heat resistance are characterized by a constant parameter and a constant coefficient. The effects of heat transfer laws and various loss terms on the performance of the generalized irreversible Carnot Refrigerator are analysed. The obtained results include those obtained in many literatures.

Calvo A Hernandez - One of the best experts on this subject based on the ideXlab platform.

  • coefficient of performance under optimized figure of merit in minimally nonlinear irreversible Refrigerator
    EPL, 2013
    Co-Authors: Yuki Izumida, Calvo A Hernandez, Koji Okuda, J. M. M. Roco
    Abstract:

    We apply the model of minimally nonlinear irreversible heat engines developed by Izumida and Okuda (EPL, 97 (2012) 10004) to Refrigerators. The model assumes extended Onsager relations including a new nonlinear term accounting for dissipation effects. The bounds for the optimized regime under an appropriate figure of merit and the tight-coupling condition are analyzed and successfully compared with those obtained previously for low-dissipation Carnot Refrigerators in the finite-time thermodynamics framework. Besides, we study the bounds for the nontight-coupling case numerically. We also introduce a leaky low-dissipation Carnot Refrigerator and show that it serves as an example of the minimally nonlinear irreversible Refrigerator, by calculating its Onsager coefficients explicitly.