The Experts below are selected from a list of 40347 Experts worldwide ranked by ideXlab platform

Hasbi Yavuz - One of the best experts on this subject based on the ideXlab platform.

  • Optimal design of the regenerative gas turbine engine with isothermal heat addition
    Applied Energy, 2001
    Co-Authors: L.berrin Erbay, Selahattin Göktun, Hasbi Yavuz
    Abstract:

    A regenerative gas turbine engine, with isothermal heat addition, working under the frame of a Brayton cycle has been analyzed. With the purpose of having a more efficient small-sized gas turbine engine, the optimization has been carried out numerically using the Maximum Power (MP) and Maximum Power Density (MPD) method. The effects of internal irreversibilities have been considered in terms of the isentropic efficiencies of the turbine and compressor and of the regenerator efficiency. The results summarized by figures show that the regenerative gas turbine engine, with isothermal heat addition, designed according to the Maximum Power Density condition gives the best performance and exhibits highest cycle efficiencies.

  • Optimization of the irreversible Stirling heat engine
    International Journal of Energy Research, 1999
    Co-Authors: L.berrin Erbay, Hasbi Yavuz
    Abstract:

    The effects of inefficiencies in the compression, expansion and regeneration processes on engine performance have been evaluated theoretically for a Stirling heat engine operating in a closed regenerative thermodynamic cycle. The irreversible cycle has been optimized by using the Maximum Power Density technique. Maximized Power and maximized Power Density are obtained for different n ex , τ, α c , α h , η c , η ex and η reg values. The Maximum efficiencies have been found very close to the values corresponding to the Maximum Power Density conditions but far from the values at Maximum Power. It has been found that the engines designed by considering the Maximum Power Density have high efficiencies and small sizes under the same prescribed conditions.

  • Analysis of the stirling heat engine at Maximum Power conditions
    Energy, 1997
    Co-Authors: L.berrin Erbay, Hasbi Yavuz
    Abstract:

    The Stirling heat engine operating in a closed regenerative thermodynamic cycle is analyzed. Polytropic processes are used for the Power and displacement pistons. Following regeneration, the Maximum Power Density and efficiency are found and the compression ratio at Maximum Power Density is determined.

  • A performance analysis for MHD Power cycles operating at Maximum Power Density
    Journal of Physics D: Applied Physics, 1996
    Co-Authors: Bahri Sahin, Ali Kodal, Hasbi Yavuz
    Abstract:

    An analysis of the thermal efficiency of a magnetohydrodynamic (MHD) Power cycle at Maximum Power Density for a constant velocity type MHD generator has been carried out. The irreversibilities at the compressor and the MHD generator are taken into account. The results obtained from Power Density analysis were compared with those of Maximum Power analysis. It is shown that by using the Power Density criteria the MHD cycle efficiency can be increased effectively.

  • Maximum Power Density analysis of an irreversible Joule - Brayton engine
    Journal of Physics D: Applied Physics, 1996
    Co-Authors: Bahri Sahin, Ali Kodal, Tamer Yilmaz, Hasbi Yavuz
    Abstract:

    A performance analysis based on a Power Density criterion has been carried out for an irreversible Joule - Brayton (JB) heat engine. The results obtained were compared with those of a Power performance criterion. It is shown that design parameters at Maximum Power Density lead to smaller and more efficient JB engines than an engine working at Maximum Power output conditions. Due to irreversibilities in the heat engine, the Power and thermal efficiency will reduce by a certain amount, however the Maximum Power Density conditions still give a better performance than at the Maximum Power output conditions. The analysis demonstrated in this paper may provide a basis for the determination of optimal operating conditions and the design parameters for real JB heat engines.

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

  • Power Density optimisation of an endoreversible closed variable-temperature heat reservoir intercooled regenerated Brayton cycle
    International Journal of Ambient Energy, 2006
    Co-Authors: Lingen Chen, Junhua Wang, Fengrui Sun
    Abstract:

    SYNOPSIS Taking Power Density, defined as the ratio of Power output to the Maximum specific volume in the cycle, as the objective function, this paper applies the theory of finite time thermodynamics to find the optimal distribution of heat conductance of the hot- and cold-side heat exchangers, the optimal intercooling pressure ratio, the optimal total pressure ratio and the optimal heat capacity ratio between working fluid and heat reservoir of an endoreversible closed intercooled regenerated Brayton cycle coupled to variable-temperature heat reservoirs with heat resistance losses in the hot- and cold-side heat exchangers, the intercooler and the regenerator, by using detailed numerical calculation. The Maximum Power Density, the double-Maximum Power Density and the triple-Maximum Power Density are obtained by optimisation. The effects of some design parameters, including the cycle inlet heat reservoir temperature ratio, the inlet temperature ratio of cooling fluid in the intercooler and the cold-side he...

  • Performance comparison of an irreversible closed variable-temperature heat reservoir brayton cycle under Maximum Power Density and Maximum Power conditions
    Proceedings of the Institution of Mechanical Engineers Part A: Journal of Power and Energy, 2005
    Co-Authors: Lingen Chen, Junlin Zheng, Fengrui Sun
    Abstract:

    The Power Density is taken as an objective for performance analysis of an irreversible closed Brayton cycle coupled to variable-temperature heat reservoirs. The analytical formulas about the relationship between Power Density and working fluid temperature ratio (pressure ratio) are derived with the heat resistance losses in the hot- and cold-side heat exchangers, the irreversible compression and expansion losses in the compressor and turbine, and the effect of the finite thermal capacity rate of the heat reservoirs. The obtained results are compared with those results obtained by using the Maximum Power criterion. The influences of some design parameters, including the temperature ratio of the heat reservoirs, the effective-nesses of the heat exchangers between the working fluid and the heat reservoirs, and the efficiencies of the compressor and the turbine, on the Maximum Power Density are provided by numerical examples, and the advantages and disadvantages of Maximum Power Density design are analysed. The Power plant design with Maximum Power Density leads to a higher efficiency and smaller size. When the heat transfers between the working fluid and the heat reservoirs are carried out ideally and the thermal capacity rates of the heat reservoirs are infinite, the results of this article become similar to those obtained in the recent literature.

  • performance comparison of an endoreversible closed variable temperature heat reservoir brayton cycle under Maximum Power Density and Maximum Power conditions
    Energy Conversion and Management, 2002
    Co-Authors: Lingen Chen, Junlin Zheng, Fengrui Sun
    Abstract:

    In this paper, the Power Density, defined as the ratio of Power output to Maximum specific volume in the cycle, is taken as the objective for performance analysis of an endoreversible closed Brayton cycle coupled to variable temperature heat reservoirs in the viewpoint of finite time thermodynamics or entropy generation minimization. The analytical formulae about the relations between Power Density and pressure ratio are derived with heat resistance losses in the hot and cold side heat exchangers. The obtained results are compared with those results obtained by using the Maximum Power criterion. The influences of some design parameters on the Maximum Power Density are provided by numerical examples, and the advantages and disadvantages of Maximum Power Density design are analyzed. The Power plant design with Maximum Power Density leads to a higher efficiency and smaller size. When the heat transfer is effected ideally and the thermal capacity rates of the two heat reservoirs are infinite, the results of this paper become those obtained in recent literature.

  • Performance comparison of an irreversible closed Brayton cycle under Maximum Power Density and Maximum Power conditions
    Exergy An International Journal, 2002
    Co-Authors: Lingen Chen, Junlin Zheng, Fengrui Sun
    Abstract:

    Abstract In this paper, the Power Density, defined as the ratio of Power output to the Maximum specific volume in the cycle, is taken as objective for performance analysis of an irreversible closed Brayton cycle coupled to constant-temperature heat reservoirs in the viewpoint of finite time thermodynamics (FTT) or entropy generation minimization (EGM). The analytical formulas about the relations between Power Density and pressure ratio are derived with the heat resistance losses in the hot- and cold-side heat exchangers and the irreversible compression and expansion losses in the compressor and turbine. The obtained results are compared with those results obtained by using the Maximum Power criterion. The influences of some design parameters on the Maximum Power Density are provided by numerical examples, and the advantages and disadvantages of Maximum Power Density design are analyzed. The Power plant design with Maximum Power Density leads to a higher efficiency and smaller size. However, the Maximum Power Density design requires a higher pressure ratio than Maximum Power design. When the heat transfer is carried out ideally, the results of this paper become those obtained in recent literature.

  • Efficiency of an Atkinson engine at Maximum Power Density
    Energy Conversion and Management, 1998
    Co-Authors: Lingen Chen, Junxing Lin, Fengrui Sun
    Abstract:

    In studies of finite-time thermodynamics, most performance analyses concern the Maximum Power output and the corresponding efficiency for heat engines. In this paper, instead of just maximizing Power for a cycle, the Power Density (the ratio of the Power to the Maximum specific volume in the cycle) is maximized for an Atkinson engine. The results showed that the efficiency at Maximum Power Density is always greater than that at Maximum Power, and the design parameters at Maximum Power Density lead to smaller and more efficient Atkinson engines with larger pressure ratios.

Irini Angelidaki - One of the best experts on this subject based on the ideXlab platform.

  • Surface area expansion of electrodes with grass-like nanostructures and gold nanoparticles to enhance electricity generation in microbial fuel cells.
    Bioresource technology, 2012
    Co-Authors: Fatima Alzahraa Alatraktchi, Yifeng Zhang, Jafar Safaa Noori, Irini Angelidaki
    Abstract:

    Abstract Microbial fuel cells (MFCs) have applications possibilities for wastewater treatment, biotransformation, and biosensor, but the development of highly efficient electrode materials is critical for enhancing the Power generation. Two types of electrodes modified with nanoparticles or grass-like nanostructure (termed nanograss) were used. A two-chamber MFC with plain silicium electrodes achieved a Maximum Power Density of 0.002 mW/m 2 , while an electrode with nanograss of titanium and gold deposited on one side gave a Maximum Power Density of 2.5 mW/m 2 . Deposition of titanium and gold on both sides of plain silicium showed a Maximum Power Density of 86.0 mW/m 2 . Further expanding the surface area of carbon-paper electrodes with gold nanoparticles resulted in a Maximum stable Power Density of 346.9 mW/m 2 which is 2.9 times higher than that achieved with conventional carbon-paper. These results show that fabrication of electrodes with nanograss could be an efficient way to increase the Power generation.

  • Submersible microbial fuel cell for electricity production from sewage sludge.
    Water Science and Technology, 2011
    Co-Authors: Yifeng Zhang, Lola Gonzalez Olias, Prawit Kongjan, Irini Angelidaki
    Abstract:

    A submersible microbial fuel cell (SMFC) was utilized to treat sewage sludge and simultaneously generate electricity. Stable Power generation (145 ± 5 mW/m 2 , 470 Ω) was produced continuously from raw sewage sludge for 5.5 days. The Maximum Power Density reached 190 ± 5 mW/m 2 . The corresponding total chemical oxygen demand (TCOD) removal efficiency was 78.1 ± 0.2% with initial TCOD of 49.7 g/L. The Power generation of SMFC was depended on the sludge concentration, while dilution of the raw sludge resulted in higher Power Density. The Maximum Power Density was saturated at sludge concentration of 17 g-TCOD/L, where 290 mW/m 2 was achieved. When effluents from an anaerobic digester that was fed with raw sludge were used as substrate in the SMFC, a Maximum Power Density of 318 mW/m 2 , and a final TCOD removal of 71.9 ± 0.2% were achieved. These results have practical implications for development of an effective system to treat sewage sludge and simultaneously recover energy.

  • Submersible microbial fuel cell for electricity production from sewage sludge.
    Water science and technology : a journal of the International Association on Water Pollution Research, 2011
    Co-Authors: Yifeng Zhang, Lola Gonzalez Olias, Prawit Kongjan, Irini Angelidaki
    Abstract:

    A submersible microbial fuel cell (SMFC) was utilized to treat sewage sludge and simultaneously generate electricity. Stable Power generation (145 +/- 5 mW/m2, 470 omega) was produced continuously from raw sewage sludge for 5.5 days. The Maximum Power Density reached 190 +/- 5 mW/m2. The corresponding total chemical oxygen demand (TCOD) removal efficiency was 78.1 +/- 0.2% with initial TCOD of 49.7 g/L. The Power generation of SMFC was depended on the sludge concentration, while dilution of the raw sludge resulted in higher Power Density. The Maximum Power Density was saturated at sludge concentration of 17 g-TCOD/L, where 290 mw/m2 was achieved. When effluents from an anaerobic digester that was fed with raw sludge were used as substrate in the SMFC, a Maximum Power Density of 318 mW/m2, and a final TCOD removal of 71.9 +/- 0.2% were achieved. These results have practical implications for development of an effective system to treat sewage sludge and simultaneously recover energy.

  • Importance of temperature and anodic medium composition on microbial fuel cell (MFC) performance
    Biotechnology Letters, 2008
    Co-Authors: Booki Min, Óscar Benito Román, Irini Angelidaki
    Abstract:

    The performance of a microbial fuel cell (MFC) was investigated at different temperatures and anodic media. A lag phase of 30 h occurred at 30°C which was half that at room temperature (22°C). The Maximum Power Density at 30°C was 70 mW/m^2 and at 22°C was 43 mW/m^2. At 15°C, no successful operation was observed even after several loadings for a long period of operation. Maximum Power Density of 320 mW/m^2 was obtained with wastewater medium containing phosphate buffer (conductivity: 11.8 mS/cm), which was approx. 4 times higher than the value without phosphate additions (2.89 mS/cm).

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

  • Power Density optimisation of an endoreversible closed variable-temperature heat reservoir intercooled regenerated Brayton cycle
    International Journal of Ambient Energy, 2006
    Co-Authors: Lingen Chen, Junhua Wang, Fengrui Sun
    Abstract:

    SYNOPSIS Taking Power Density, defined as the ratio of Power output to the Maximum specific volume in the cycle, as the objective function, this paper applies the theory of finite time thermodynamics to find the optimal distribution of heat conductance of the hot- and cold-side heat exchangers, the optimal intercooling pressure ratio, the optimal total pressure ratio and the optimal heat capacity ratio between working fluid and heat reservoir of an endoreversible closed intercooled regenerated Brayton cycle coupled to variable-temperature heat reservoirs with heat resistance losses in the hot- and cold-side heat exchangers, the intercooler and the regenerator, by using detailed numerical calculation. The Maximum Power Density, the double-Maximum Power Density and the triple-Maximum Power Density are obtained by optimisation. The effects of some design parameters, including the cycle inlet heat reservoir temperature ratio, the inlet temperature ratio of cooling fluid in the intercooler and the cold-side he...

  • Performance comparison of an irreversible closed variable-temperature heat reservoir brayton cycle under Maximum Power Density and Maximum Power conditions
    Proceedings of the Institution of Mechanical Engineers Part A: Journal of Power and Energy, 2005
    Co-Authors: Lingen Chen, Junlin Zheng, Fengrui Sun
    Abstract:

    The Power Density is taken as an objective for performance analysis of an irreversible closed Brayton cycle coupled to variable-temperature heat reservoirs. The analytical formulas about the relationship between Power Density and working fluid temperature ratio (pressure ratio) are derived with the heat resistance losses in the hot- and cold-side heat exchangers, the irreversible compression and expansion losses in the compressor and turbine, and the effect of the finite thermal capacity rate of the heat reservoirs. The obtained results are compared with those results obtained by using the Maximum Power criterion. The influences of some design parameters, including the temperature ratio of the heat reservoirs, the effective-nesses of the heat exchangers between the working fluid and the heat reservoirs, and the efficiencies of the compressor and the turbine, on the Maximum Power Density are provided by numerical examples, and the advantages and disadvantages of Maximum Power Density design are analysed. The Power plant design with Maximum Power Density leads to a higher efficiency and smaller size. When the heat transfers between the working fluid and the heat reservoirs are carried out ideally and the thermal capacity rates of the heat reservoirs are infinite, the results of this article become similar to those obtained in the recent literature.

  • performance comparison of an endoreversible closed variable temperature heat reservoir brayton cycle under Maximum Power Density and Maximum Power conditions
    Energy Conversion and Management, 2002
    Co-Authors: Lingen Chen, Junlin Zheng, Fengrui Sun
    Abstract:

    In this paper, the Power Density, defined as the ratio of Power output to Maximum specific volume in the cycle, is taken as the objective for performance analysis of an endoreversible closed Brayton cycle coupled to variable temperature heat reservoirs in the viewpoint of finite time thermodynamics or entropy generation minimization. The analytical formulae about the relations between Power Density and pressure ratio are derived with heat resistance losses in the hot and cold side heat exchangers. The obtained results are compared with those results obtained by using the Maximum Power criterion. The influences of some design parameters on the Maximum Power Density are provided by numerical examples, and the advantages and disadvantages of Maximum Power Density design are analyzed. The Power plant design with Maximum Power Density leads to a higher efficiency and smaller size. When the heat transfer is effected ideally and the thermal capacity rates of the two heat reservoirs are infinite, the results of this paper become those obtained in recent literature.

  • Performance comparison of an irreversible closed Brayton cycle under Maximum Power Density and Maximum Power conditions
    Exergy An International Journal, 2002
    Co-Authors: Lingen Chen, Junlin Zheng, Fengrui Sun
    Abstract:

    Abstract In this paper, the Power Density, defined as the ratio of Power output to the Maximum specific volume in the cycle, is taken as objective for performance analysis of an irreversible closed Brayton cycle coupled to constant-temperature heat reservoirs in the viewpoint of finite time thermodynamics (FTT) or entropy generation minimization (EGM). The analytical formulas about the relations between Power Density and pressure ratio are derived with the heat resistance losses in the hot- and cold-side heat exchangers and the irreversible compression and expansion losses in the compressor and turbine. The obtained results are compared with those results obtained by using the Maximum Power criterion. The influences of some design parameters on the Maximum Power Density are provided by numerical examples, and the advantages and disadvantages of Maximum Power Density design are analyzed. The Power plant design with Maximum Power Density leads to a higher efficiency and smaller size. However, the Maximum Power Density design requires a higher pressure ratio than Maximum Power design. When the heat transfer is carried out ideally, the results of this paper become those obtained in recent literature.

  • Power Density Optimization for an Irreversible Closed Brayton Cycle
    Open Systems & Information Dynamics, 2001
    Co-Authors: Lingen Chen
    Abstract:

    In this paper, the Power Density, defined as the ratio of Power output to the Maximum specific volume in the cycle, is taken as objective for performance optimization of an irreversible closed Brayton cycle coupled to constant-temperature heat reservoirs in the viewpoint of finite time thermodynamics (FTT) or entropy generation minimization (EGM). The analytical formulas about the relations between Power Density and pressure ratio are derived with the heat resistance losses in the hot- and cold-side heat exchangers and the irreversible compression and expansion losses in the compressor and turbine. The Maximum Power Density optimization is performed by searching the optimum heat conductance distribution corresponding to the optimum Power Density of the hot- and cold- side heat exchangers for the fixed heat exchanger inventory. The influence of some design parameters on the optimum heat conductance distribution, the Maximum Power Density, and the optimum pressure ratio corresponding to the Maximum Power Density are provided. The Power plant design with optimization leads to a higher efficiency and smaller size including the compressor, turbine, and the hot- and cold-side heat exchangers.

Ali Kodal - One of the best experts on this subject based on the ideXlab platform.

  • A comparative performance analysis of irreversible Carnot heat engines under Maximum Power Density and Maximum Power conditions
    Energy Conversion and Management, 2000
    Co-Authors: Ali Kodal, Bahri Sahin, Tamer Yilmaz
    Abstract:

    This paper reports the finite time thermodynamic optimization based on the Maximum Power Density criterion for an irreversible Carnot heat engine model which includes three types of irreversibilities: finite rate heat transfer, heat leakage and internal irreversibility. The obtained results are compared with those results obtained by using the Maximum Power criterion. The design parameters under the optimal conditions have been derived analytically and the effects of the irreversibilities on the general and optimal performances are investigated. The results showed that the design parameters at Maximum Power Density lead to smaller and more efficient heat engines. It is also seen that the irreversibilities have a greater influence on the performances at Maximum Power Density conditions with respect to the ones at Maximum Power conditions. Also in this study, the optimal conductance allocation parameter is investigated at both Maximum Power Density and Maximum Power conditions by assuming a constrained total thermal conductance in the case when there is no heat leakage. The relation between the conductance allocation parameter and the thermal efficiencies at Maximum Power Density and Maximum Power is also investigated. The obtained results generalize the result of previous studies on this subject and provide guidance to optimal design in terms of Power, thermal efficiency and engine sizes for real heat engines.

  • Maximum Power Density analysis for irreversible combined Carnot cycles
    Journal of Physics D: Applied Physics, 1999
    Co-Authors: Ali Kodal
    Abstract:

    A finite-time thermodynamic optimization based on the Maximum Power Density criterion for an irreversible combined Carnot heat engine model has been carried out. The effects of the finite-rate heat transfer, internal irreversibility and heat leak are considered in the analysis. The obtained results are compared with those results obtained by using the Maximum Power criterion. The design parameters under the optimal conditions were derived analytically and the effects of irreversibilities on the general and the optimal performances are investigated.

  • A comparative performance analysis of irreversible regenerative reheating Joule-Brayton engines under Maximum Power Density and Maximum Power conditions
    Journal of Physics D: Applied Physics, 1998
    Co-Authors: Bahri Sahin, Ali Kodal, Salih Saim Kaya
    Abstract:

    A performance analysis based on the Maximum Power Density criterion has been carried out for an irreversible regenerative reheating Joule-Brayton engine. The obtained results were compared with those obtained using the Maximum Power performance criterion. The design parameters under the optimal conditions have been derived analytically and their effects on the engine's performance have been discussed. The overall effects of reheating, regeneration and internal irreversibilities are investigated. The obtained results may provide a general theoretical tool for the optimal design and operation of real non-regenerative and regenerative reheating gas turbines.

  • A performance analysis for MHD Power cycles operating at Maximum Power Density
    Journal of Physics D: Applied Physics, 1996
    Co-Authors: Bahri Sahin, Ali Kodal, Hasbi Yavuz
    Abstract:

    An analysis of the thermal efficiency of a magnetohydrodynamic (MHD) Power cycle at Maximum Power Density for a constant velocity type MHD generator has been carried out. The irreversibilities at the compressor and the MHD generator are taken into account. The results obtained from Power Density analysis were compared with those of Maximum Power analysis. It is shown that by using the Power Density criteria the MHD cycle efficiency can be increased effectively.

  • Maximum Power Density analysis of an irreversible Joule - Brayton engine
    Journal of Physics D: Applied Physics, 1996
    Co-Authors: Bahri Sahin, Ali Kodal, Tamer Yilmaz, Hasbi Yavuz
    Abstract:

    A performance analysis based on a Power Density criterion has been carried out for an irreversible Joule - Brayton (JB) heat engine. The results obtained were compared with those of a Power performance criterion. It is shown that design parameters at Maximum Power Density lead to smaller and more efficient JB engines than an engine working at Maximum Power output conditions. Due to irreversibilities in the heat engine, the Power and thermal efficiency will reduce by a certain amount, however the Maximum Power Density conditions still give a better performance than at the Maximum Power output conditions. The analysis demonstrated in this paper may provide a basis for the determination of optimal operating conditions and the design parameters for real JB heat engines.