The Experts below are selected from a list of 108924 Experts worldwide ranked by ideXlab platform
Eckhard A. Groll - One of the best experts on this subject based on the ideXlab platform.
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modeling of a semi hermetic co2 reciprocating compressor including lubrication submodels for piston rings and bearings
International Journal of Refrigeration-revue Internationale Du Froid, 2013Co-Authors: Bin Yang, Craig R Bradshaw, Eckhard A. GrollAbstract:A comprehensive model for a semi-hermetic CO2 reciprocating compressor is presented. This comprehensive model is composed of three main sub-models simulating the geometry and kinematics, the Compression Process, and frictional power loss. Valve and leakage sub-models are included in the Compression Process model. The frictional power loss model includes the friction at the bearings and between the piston ring and cylinder wall. The predicted results of the comprehensive model are validated using external compressor performance measurements of compressor input power and mass flow rate. The mass flow rate and compressor input power are predicted to within 4.03% and 6.43% mean absolute error, respectively, compared to the experimental datum. Additionally, a parametric study is presented which investigates compressor performance as a function of the stroke-to-bore ratio.
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modeling of hermetic scroll compressors model development
Hvac&r Research, 2004Co-Authors: Yu Chen, James E. Braun, Eckhard A. GrollAbstract:This paper presents a comprehensive model for a hermetic scroll compressor. The model combines models of the Compression Process including leakage and local heat transfer within the scrolls, frictional losses, motor inefficiencies, and heat transfer within the shell and to the ambient. The model is useful for investigating the impact of design changes on compressor performance. Some sample results are presented in this paper. Detailed validation and an investigation of compressor design improvements are described in a companion paper.
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modeling and testing of an automobile ac scroll compressor part i model development
2004Co-Authors: Eckhard A. Groll, James A BraunAbstract:This paper presents the details of an overall simulation model that predicts the performance of an automobile air conditioning scroll compressor. Using the overall model, the compressor performance and discharge temperature can be predicted at specific operating conditions. The model will be used in the future to optimize the design of automobile air conditioning scroll compressors. The model was developed based on an investigation of the geometric characteristic of an existing compressor, the modeling of the Compression Process, and an efficiency analysis. The pre-Compression at the end of the suction Process and re-Compression at the discharge angle are taken into account in the Process model. Tangential leakage and radial leakage during the Compression Process are investigated within the efficiency analysis. The influence of superheat and heat transfer during the Compression Process on performance are also taken into account within the efficiency analysis.
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mathematical modeling of scroll compressors part ii overall scroll compressor modeling
International Journal of Refrigeration-revue Internationale Du Froid, 2002Co-Authors: Yu Chen, James E. Braun, Nils P. Halm, Eckhard A. GrollAbstract:Abstract This paper presents the development of a comprehensive simulation model of a horizontal scroll compressor, which combines a detailed Compression Process model (Chen Y., Halm N., Groll E., Braun J. Mathematical modelling of scroll compressors — part I: Compression Process modeling, International Journal of Refrigeration 2002;25(6):731–750) and an overall compressor model. In the overall model, compressor components are analyzed in terms of nine different elements. Steady state energy balance equations are established applying the lumped capacitance method. In combination with the detailed Compression Process model, these equations were implemented into computer code and solved recursively. In this way, the temperature and pressure of the refrigerant in different compressor chambers, the temperature distributions in the scroll wraps, and the temperatures of the other compressor elements can be obtained. Thereafter, power consumption and efficiency of the compressor can be calculated. Tests were used to verify the overall model on a macroscopic basis. Using the simulation program based on the overall compressor model, a parametric study of the scroll compressor was performed, and the effects of internal leakage and heat transfer losses were investigated and some preliminary results were obtained. These results indicate that the comprehensive scroll compressor model is capable of predicting real compressor behavior and useful to the design and optimization of scroll compressors.
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mathematical modeling of scroll compressors part i Compression Process modeling
International Journal of Refrigeration-revue Internationale Du Froid, 2002Co-Authors: Yu Chen, Eckhard A. Groll, Nils P. Halm, James E. BraunAbstract:This paper presents a detailed model for the Compression Process of a scroll compressor, which is used for investigating a compressor's performance under different operating conditions and subject to design changes. Upon defining the compressor chambers as suction chambers, Compression chambers and discharge chambers, a geometry study was conducted and the governing mass and energy conservation equations were developed for each chamber. Models for the refrigerant flow in the suction and discharge Processes, radial and flank leakage, and heat transfer between the gas and scroll wraps were combined with the conservation equations. The state of the refrigerant changes with a period of angle 2π, and thousands of step are used to solve the governing differential equations during each period. It is assumed that in each step the compressor is in steady state. Since the differential equations for the different chambers are coupled, all these equations are solved simultaneously using a nonlinear equation solver. A description of the corresponding computer code and some results are included in this paper. Verification of the Compression Process model can be referred to that of the overall model, which is described in Chen et al. [Chen Y, Halm N, Braun J, Groll E. Mathematical modeling of scroll compressors—part II: overall scroll compressor modeling. International Journal of Refrigeration 2002;25(6):751–764.].
Demos P. Georgiou - One of the best experts on this subject based on the ideXlab platform.
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The effects of a multistep intercooled Compression Process implemented on a solar-driven Braysson heat engine
Energy Conversion and Management, 2015Co-Authors: Demos P. Georgiou, Kf Milidonis, Eleutherios N. GeorgiouAbstract:The present study develops the thermodynamic analysis for the cycle of a solar-driven, Braysson cycle based plant in the ideal limit and in the presence of Process irreversibilities. The plant cycle differs from the conventional idealized Braysson cycle in that the implementation of the final isothermal Compression Process is substituted by a multistep intercooled Compression. The cycle’s efficiency is analytically formulated after taking into account several loss (irreversibility) sources such as the non-isentropic behavior of the main compressor, the power turbine and the intercooled compressor stages as well as the actual heat transferred through countercurrent heat exchangers. All pressure losses associated with heat exchangers are related to the actual heat transfer load within each exchanger. The analysis develops a parametric evaluation for the effectiveness of the main cycle free variables on the thermal efficiency of the cycle. Such free variables include the working fluid maximum temperature, the compressor pressure ratio and the operating temperature limits of the intercooled Compression stages, in addition to the polytropic coefficients of the compressor and power turbine (quasi-) isentropic Processes. The results indicate that such a plant may reach efficiency levels above 30%, i.e. exceeding the efficiencies of the conventional Photovoltaic plants by a wide margin.
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useful work and the thermal efficiency in the ideal lenolr cycle with regenerative preheating
Journal of Applied Physics, 2000Co-Authors: Demos P. GeorgiouAbstract:In the existing thermal engine concepts negative work transfer (usually needed to drive a Compression Process) is supplied by the work produced by the engine itself. The remaining difference (i.e., the net work transfer) becomes the useful work, since it is available for external consumption. The thermal efficiency is the parameter that compares this against the heat input into the system. It forms the main optimization parameter in any engine design. The objective of the present study is to show that for the case of the Lenoir cycle with regenerative preheating the entire positive work is available for external consumption, since the negative (i.e., the Compression) work is supplied by the atmospheric air. Not only this, but, during the Compression Process and due to the pressure difference across the two sides of the moving piston, an additional (useful) work transfer may be generated. Thus, the proposed power plant may be considered as a combination of a thermal engine and a wind turbine. In the ideal cycle limit (at least), the total amount of useful work exceeds the heat entering the system. This leads to the definition of a new parameter for the efficiency (called the technical efficiency), which compares the combined positive work transfer (i.e., the useful one) against the heat entering the system and which may exceed the 100% level.
Haisheng Chen - One of the best experts on this subject based on the ideXlab platform.
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off design performance and an optimal operation strategy for the multistage Compression Process in adiabatic compressed air energy storage systems
Applied Thermal Engineering, 2019Co-Authors: Yujie Xu, Qi Liang, Xinjing Zhang, Yi Zhang, Hongtao Tang, Haisheng ChenAbstract:Abstract Compressed air energy storage (CAES) systems usually operate under off-design conditions due to load fluctuations, environmental factors, and performance characteristics of the system. Thus, to improve design and operation characteristics, it is important to study off-design performance of CAES systems. The Compression Process plays an important role in CAES systems. In this paper, we discuss the methodology for modeling off-design operation of a multistage Compression Process with intercooling of the most promising adiabatic CAES (A-CAES) system. The off-design performances under two proposed kinds of operating regulations are analyzed and compared. These two operating regulations are equal-power-ratio regulation (EPR) and optimizing variable inlet guide vane rotation angle (OVRA) (optimizing all stages simultaneously) regulation. Correlation between parameters such as total power consumption ratio, exergy efficiency, hot water temperature versus mass flow rate ratio, and back pressure is revealed in depth. Based on this research, the optimal operation laws, including pressure ratio distribution and efficiency distribution among all stages, are obtained, and it is found that the primary optimum principle is to enhance the isentropic efficiencies of low-pressure stages to approach design point. Finally, the optimized regulating law for the inlet guide vane rotation angles of the 4 stages is revealed. This study provides strong support for the design, operation, and control of CAES systems.
Eleutherios N. Georgiou - One of the best experts on this subject based on the ideXlab platform.
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The effects of a multistep intercooled Compression Process implemented on a solar-driven Braysson heat engine
Energy Conversion and Management, 2015Co-Authors: Demos P. Georgiou, Kf Milidonis, Eleutherios N. GeorgiouAbstract:The present study develops the thermodynamic analysis for the cycle of a solar-driven, Braysson cycle based plant in the ideal limit and in the presence of Process irreversibilities. The plant cycle differs from the conventional idealized Braysson cycle in that the implementation of the final isothermal Compression Process is substituted by a multistep intercooled Compression. The cycle’s efficiency is analytically formulated after taking into account several loss (irreversibility) sources such as the non-isentropic behavior of the main compressor, the power turbine and the intercooled compressor stages as well as the actual heat transferred through countercurrent heat exchangers. All pressure losses associated with heat exchangers are related to the actual heat transfer load within each exchanger. The analysis develops a parametric evaluation for the effectiveness of the main cycle free variables on the thermal efficiency of the cycle. Such free variables include the working fluid maximum temperature, the compressor pressure ratio and the operating temperature limits of the intercooled Compression stages, in addition to the polytropic coefficients of the compressor and power turbine (quasi-) isentropic Processes. The results indicate that such a plant may reach efficiency levels above 30%, i.e. exceeding the efficiencies of the conventional Photovoltaic plants by a wide margin.
James E. Braun - One of the best experts on this subject based on the ideXlab platform.
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modeling of hermetic scroll compressors model development
Hvac&r Research, 2004Co-Authors: Yu Chen, James E. Braun, Eckhard A. GrollAbstract:This paper presents a comprehensive model for a hermetic scroll compressor. The model combines models of the Compression Process including leakage and local heat transfer within the scrolls, frictional losses, motor inefficiencies, and heat transfer within the shell and to the ambient. The model is useful for investigating the impact of design changes on compressor performance. Some sample results are presented in this paper. Detailed validation and an investigation of compressor design improvements are described in a companion paper.
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mathematical modeling of scroll compressors part ii overall scroll compressor modeling
International Journal of Refrigeration-revue Internationale Du Froid, 2002Co-Authors: Yu Chen, James E. Braun, Nils P. Halm, Eckhard A. GrollAbstract:Abstract This paper presents the development of a comprehensive simulation model of a horizontal scroll compressor, which combines a detailed Compression Process model (Chen Y., Halm N., Groll E., Braun J. Mathematical modelling of scroll compressors — part I: Compression Process modeling, International Journal of Refrigeration 2002;25(6):731–750) and an overall compressor model. In the overall model, compressor components are analyzed in terms of nine different elements. Steady state energy balance equations are established applying the lumped capacitance method. In combination with the detailed Compression Process model, these equations were implemented into computer code and solved recursively. In this way, the temperature and pressure of the refrigerant in different compressor chambers, the temperature distributions in the scroll wraps, and the temperatures of the other compressor elements can be obtained. Thereafter, power consumption and efficiency of the compressor can be calculated. Tests were used to verify the overall model on a macroscopic basis. Using the simulation program based on the overall compressor model, a parametric study of the scroll compressor was performed, and the effects of internal leakage and heat transfer losses were investigated and some preliminary results were obtained. These results indicate that the comprehensive scroll compressor model is capable of predicting real compressor behavior and useful to the design and optimization of scroll compressors.
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mathematical modeling of scroll compressors part i Compression Process modeling
International Journal of Refrigeration-revue Internationale Du Froid, 2002Co-Authors: Yu Chen, Eckhard A. Groll, Nils P. Halm, James E. BraunAbstract:This paper presents a detailed model for the Compression Process of a scroll compressor, which is used for investigating a compressor's performance under different operating conditions and subject to design changes. Upon defining the compressor chambers as suction chambers, Compression chambers and discharge chambers, a geometry study was conducted and the governing mass and energy conservation equations were developed for each chamber. Models for the refrigerant flow in the suction and discharge Processes, radial and flank leakage, and heat transfer between the gas and scroll wraps were combined with the conservation equations. The state of the refrigerant changes with a period of angle 2π, and thousands of step are used to solve the governing differential equations during each period. It is assumed that in each step the compressor is in steady state. Since the differential equations for the different chambers are coupled, all these equations are solved simultaneously using a nonlinear equation solver. A description of the corresponding computer code and some results are included in this paper. Verification of the Compression Process model can be referred to that of the overall model, which is described in Chen et al. [Chen Y, Halm N, Braun J, Groll E. Mathematical modeling of scroll compressors—part II: overall scroll compressor modeling. International Journal of Refrigeration 2002;25(6):751–764.].