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Ştefan Grigorean - One of the best experts on this subject based on the ideXlab platform.

  • studies on Closed irreversible Cycles analysis based on finite physical dimensions thermodynamics
    Newest Updates in Physical Science Research Vol. 4, 2021
    Co-Authors: Gheorghe Dumitrascu, Michel Feidt, Ştefan Grigorean
    Abstract:

    The paper develops generalizing entropic approaches of irreversible Closed Cycles. The mathematical models might be applied to four possible operating irreversible trigeneration Cycles. The models involve the reference entropy, the number of internal irreversibility, the thermal conductance inventory, the proper temperatures of external heat reservoirs, the mean log temperature differences, and four possible designing operational constraints. The reference entropy is always the entropy variation rate of the working fluid during the reversible heat input. The number of internal irreversibility allows the evaluation of the reversible heat output via the ratio of overall internal irreversible entropy generation and the reference entropy. The designing operational constraints allow the replacement of the reference entropy function of the convenient finite physical dimensions parameters. The paper presents initially the number of internal irreversibility and the energy efficiency equations for engine and refrigeration Cycles. The second part develops, as an example, the influences between the imposed operational constraint and the maximum temperature on the cycle as a finite physical dimensions parameter for the basic Joule – Brayton irreversible cycle. The third part is applying the mathematical models to four possible standalone trigeneration Cycles. It was assumed that there are the required consumers of the all useful heat delivered by the trigeneration system. The design of trigeneration system must know the ratios of refrigeration rate to power and of the useful heat rate to power.

  • Finite Physical Dimensions Thermodynamics Analysis and Design of Closed Irreversible Cycles
    'MDPI AG', 2021
    Co-Authors: Gheorghe Dumitrascu, Michel Feidt, Ştefan Grigorean
    Abstract:

    This paper develops simplifying entropic models of irreversible Closed Cycles. The entropic models involve the irreversible connections between external and internal main operational parameters with finite physical dimensions. The external parameters are the mean temperatures of external heat reservoirs, the heat transfers thermal conductance, and the heat transfer mean log temperatures differences. The internal involved parameters are the reference entropy of the cycle and the internal irreversibility number. The cycle’s design might use four possible operational constraints in order to find out the reference entropy. The internal irreversibility number allows the evaluation of the reversible heat output function of the reversible heat input. Thus the cycle entropy balance equation to design the trigeneration Cycles only through external operational parameters might be involved. In designing trigeneration systems, they must know the requirements of all consumers of the useful energies delivered by the trigeneration system. The conclusions emphasize the complexity in designing and/or optimizing the irreversible trigeneration systems

  • Closed irreversible Cycles analysis based on finite physical dimensions thermodynamics
    2020
    Co-Authors: Gheorghe Dumitrascu, Michel Feidt, Ştefan Grigorean
    Abstract:

    The paper develops generalizing entropic approaches of irreversible Closed Cycles. The mathematical models of the irreversible engines (basic, with internal regeneration of the heat, cogeneration units) and of the refrigeration Cycles were applied to four possible operating irreversible trigeneration Cycles. The models involve the reference entropy, the number of internal irreversibility, the thermal conductance inventory, the proper temperatures of external heat reservoirs unifying the first law of thermodynamics and the linear heat transfer law, the mean log temperature differences, and four possible operational constraints, i.e., constant heat input, constant power, constant energy efficiency and constant reference entropy. The reference entropy is always the entropy variation rate of the working fluid during the reversible heat input process. The number of internal irreversibility allows the evaluation of the heat output via the ratio of overall internal irreversible entropy generation and the reference entropy. The operational constraints allow the replacement of the reference entropy function of the finite physical dimensions parameters, i.e., mean log temperature differences, thermal conductance inventory, and the proper external heat reservoir temperatures. The paper presents initially the number of internal irreversibility and the energy efficiency equations for engine and refrigeration Cycles. At the limit, i.e., endoreversibility, we can re-obtain the endoreversible energy efficiency equation. The second part develops the influences between the imposed operational constraint and the finite physical dimensions parameters for the basic irreversible cycle. The third part is applying the mathematical models to four possible standalone trigeneration Cycles. It was assumed that there are the required consumers of the all useful heat delivered by the trigeneration system. The design of trigeneration system must know the ratio of refrigeration rate to power, e.g., engine shaft power or useful power delivered directly to power consumers. The final discussions and conclusions emphasize the novelties and the complexity of interconnected irreversible trigeneration systems design/optimization.

Theodosios Korakianitis - One of the best experts on this subject based on the ideXlab platform.

  • An Assessment of the Performance of Closed Cycles With and Without Heat Rejection at Cryogenic Temperatures
    Journal of Engineering for Gas Turbines and Power, 1999
    Co-Authors: A Agazzani, Aristide F Massardo, Theodosios Korakianitis
    Abstract:

    This paper presents optimized cycle performance that can be obtained with systems including a Closed cycle gas turbine (CCGT). The influence of maximum temperature, minimum temperature, and recuperator effectiveness on cycle performance is illustrated. Several power-plant arrangements are analyzed and compared based on thermodynamic performance (thermal efficiency and specific work); enabling technologies (available at present); and developing technologies (available in the near term of future). The work includes the effects of utilization of high temperature ceramic heat exchangers and of coupling of CCGT systems with plants vaporizing liquid hydrogen (LH{sub 2}) or liquefied natural gas (LNG). Given the versatility of energy addition and rejection sources that can be utilized in Closed gas-cycle systems, the thermodynamic performance of power plants shown in this paper indicate the remarkable capabilities and possibilities for Closed gas-cycle systems.

  • an assessment of the performance of Closed Cycles with and without heat rejection at cryogenic temperatures
    Volume 3: Coal Biomass and Alternative Fuels; Combustion and Fuels; Oil and Gas Applications; Cycle Innovations, 1996
    Co-Authors: A Agazzani, Aristide F Massardo, Theodosios Korakianitis
    Abstract:

    This paper presents optimized cycle performance that can be obtained with systems including a Closed Cycle Gas Turbine (CCGT). The influence of maximum temperature, minimum temperature and recuperator effectiveness on cycle performance is illustrated. Several power-plant arrangements are analyzed and compared based on: thermodynamic performance (thermal efficiency and specific work); enabling technologies (available at present); and developing technologies (available in the near term or future). The work includes the effects of utilization of high temperature ceramic heat exchangers and of coupling of CCGT systems with plants vaporizing Liquid Hydrogen (LH2) or Liquefied Natural Gas (LNG). Given the versatility of energy addition and rejection sources that can be utilized in Closed gas-cycle systems, the thermodynamic performance of power plants shown in this paper indicate the remarkable capabilities and possibilities for Closed gas-cycle systems.Copyright © 1996 by ASME

T Sanchez - One of the best experts on this subject based on the ideXlab platform.

  • performance analysis of hybrid systems incorporating high temperature fuel cells and Closed cycle heat engines at part load operation
    International Journal of Hydrogen Energy, 2013
    Co-Authors: J Munoz M De Escalona, David Sanchez, Ricardo Chacartegui, T Sanchez
    Abstract:

    Abstract This work presents a comparative analysis of hybrid systems based on molten carbonate fuel cells and making use of Closed-cycle externally-heated bottoming systems. Two options are considered: reciprocating (Stirling) engines and supercritical carbon dioxide turbines. These two engines share the common feature of working on Closed Cycles with pure fluids (H2 and CO2 respectively) but, at the same time, they differ in their internal structure: Stirling engines make use of volumetric machinery whereas the supercritical carbon dioxide gas turbine (SCO2) is composed by turbomachinery. In both cases, the working fluid is subjected to very high pressures and temperatures in the range of 50–200 bar and 40–650 °C. A brief description of both bottoming systems is provided in the first sections of this article along with their expected performance in on-design and off-design (part-load) operation. The analysis of each system is therefore split into three stages. First, the most relevant features of the models of performance are discussed. Then, a comparison is shown for on-design operation aiming to evaluate the maximum efficiency attainable by the proposed engines. Finally, an analysis of off-design operation is presented. The final section of paper concludes that hybrid systems based on atmospheric fuel cells and externally heated Closed-cycle bottoming engines have the potential to outperform conventional pressurised fuel cell plus gas turbine hybrids while avoiding the demanding operating conditions on the fuel cell topping system of the latter configuration.

Gheorghe Dumitrascu - One of the best experts on this subject based on the ideXlab platform.

  • studies on Closed irreversible Cycles analysis based on finite physical dimensions thermodynamics
    Newest Updates in Physical Science Research Vol. 4, 2021
    Co-Authors: Gheorghe Dumitrascu, Michel Feidt, Ştefan Grigorean
    Abstract:

    The paper develops generalizing entropic approaches of irreversible Closed Cycles. The mathematical models might be applied to four possible operating irreversible trigeneration Cycles. The models involve the reference entropy, the number of internal irreversibility, the thermal conductance inventory, the proper temperatures of external heat reservoirs, the mean log temperature differences, and four possible designing operational constraints. The reference entropy is always the entropy variation rate of the working fluid during the reversible heat input. The number of internal irreversibility allows the evaluation of the reversible heat output via the ratio of overall internal irreversible entropy generation and the reference entropy. The designing operational constraints allow the replacement of the reference entropy function of the convenient finite physical dimensions parameters. The paper presents initially the number of internal irreversibility and the energy efficiency equations for engine and refrigeration Cycles. The second part develops, as an example, the influences between the imposed operational constraint and the maximum temperature on the cycle as a finite physical dimensions parameter for the basic Joule – Brayton irreversible cycle. The third part is applying the mathematical models to four possible standalone trigeneration Cycles. It was assumed that there are the required consumers of the all useful heat delivered by the trigeneration system. The design of trigeneration system must know the ratios of refrigeration rate to power and of the useful heat rate to power.

  • Finite Physical Dimensions Thermodynamics Analysis and Design of Closed Irreversible Cycles
    'MDPI AG', 2021
    Co-Authors: Gheorghe Dumitrascu, Michel Feidt, Ştefan Grigorean
    Abstract:

    This paper develops simplifying entropic models of irreversible Closed Cycles. The entropic models involve the irreversible connections between external and internal main operational parameters with finite physical dimensions. The external parameters are the mean temperatures of external heat reservoirs, the heat transfers thermal conductance, and the heat transfer mean log temperatures differences. The internal involved parameters are the reference entropy of the cycle and the internal irreversibility number. The cycle’s design might use four possible operational constraints in order to find out the reference entropy. The internal irreversibility number allows the evaluation of the reversible heat output function of the reversible heat input. Thus the cycle entropy balance equation to design the trigeneration Cycles only through external operational parameters might be involved. In designing trigeneration systems, they must know the requirements of all consumers of the useful energies delivered by the trigeneration system. The conclusions emphasize the complexity in designing and/or optimizing the irreversible trigeneration systems

  • Closed irreversible Cycles analysis based on finite physical dimensions thermodynamics
    2020
    Co-Authors: Gheorghe Dumitrascu, Michel Feidt, Ştefan Grigorean
    Abstract:

    The paper develops generalizing entropic approaches of irreversible Closed Cycles. The mathematical models of the irreversible engines (basic, with internal regeneration of the heat, cogeneration units) and of the refrigeration Cycles were applied to four possible operating irreversible trigeneration Cycles. The models involve the reference entropy, the number of internal irreversibility, the thermal conductance inventory, the proper temperatures of external heat reservoirs unifying the first law of thermodynamics and the linear heat transfer law, the mean log temperature differences, and four possible operational constraints, i.e., constant heat input, constant power, constant energy efficiency and constant reference entropy. The reference entropy is always the entropy variation rate of the working fluid during the reversible heat input process. The number of internal irreversibility allows the evaluation of the heat output via the ratio of overall internal irreversible entropy generation and the reference entropy. The operational constraints allow the replacement of the reference entropy function of the finite physical dimensions parameters, i.e., mean log temperature differences, thermal conductance inventory, and the proper external heat reservoir temperatures. The paper presents initially the number of internal irreversibility and the energy efficiency equations for engine and refrigeration Cycles. At the limit, i.e., endoreversibility, we can re-obtain the endoreversible energy efficiency equation. The second part develops the influences between the imposed operational constraint and the finite physical dimensions parameters for the basic irreversible cycle. The third part is applying the mathematical models to four possible standalone trigeneration Cycles. It was assumed that there are the required consumers of the all useful heat delivered by the trigeneration system. The design of trigeneration system must know the ratio of refrigeration rate to power, e.g., engine shaft power or useful power delivered directly to power consumers. The final discussions and conclusions emphasize the novelties and the complexity of interconnected irreversible trigeneration systems design/optimization.

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

  • An Assessment of the Performance of Closed Cycles With and Without Heat Rejection at Cryogenic Temperatures
    Journal of Engineering for Gas Turbines and Power, 1999
    Co-Authors: A Agazzani, Aristide F Massardo, Theodosios Korakianitis
    Abstract:

    This paper presents optimized cycle performance that can be obtained with systems including a Closed cycle gas turbine (CCGT). The influence of maximum temperature, minimum temperature, and recuperator effectiveness on cycle performance is illustrated. Several power-plant arrangements are analyzed and compared based on thermodynamic performance (thermal efficiency and specific work); enabling technologies (available at present); and developing technologies (available in the near term of future). The work includes the effects of utilization of high temperature ceramic heat exchangers and of coupling of CCGT systems with plants vaporizing liquid hydrogen (LH{sub 2}) or liquefied natural gas (LNG). Given the versatility of energy addition and rejection sources that can be utilized in Closed gas-cycle systems, the thermodynamic performance of power plants shown in this paper indicate the remarkable capabilities and possibilities for Closed gas-cycle systems.

  • an assessment of the performance of Closed Cycles with and without heat rejection at cryogenic temperatures
    Volume 3: Coal Biomass and Alternative Fuels; Combustion and Fuels; Oil and Gas Applications; Cycle Innovations, 1996
    Co-Authors: A Agazzani, Aristide F Massardo, Theodosios Korakianitis
    Abstract:

    This paper presents optimized cycle performance that can be obtained with systems including a Closed Cycle Gas Turbine (CCGT). The influence of maximum temperature, minimum temperature and recuperator effectiveness on cycle performance is illustrated. Several power-plant arrangements are analyzed and compared based on: thermodynamic performance (thermal efficiency and specific work); enabling technologies (available at present); and developing technologies (available in the near term or future). The work includes the effects of utilization of high temperature ceramic heat exchangers and of coupling of CCGT systems with plants vaporizing Liquid Hydrogen (LH2) or Liquefied Natural Gas (LNG). Given the versatility of energy addition and rejection sources that can be utilized in Closed gas-cycle systems, the thermodynamic performance of power plants shown in this paper indicate the remarkable capabilities and possibilities for Closed gas-cycle systems.Copyright © 1996 by ASME