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Maoqiong Gong - One of the best experts on this subject based on the ideXlab platform.
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performance comparison of single stage mixed refrigerant joule thomson cycle and reverse brayton cycle for cooling 80 to 120 k temperature distributed heat loads
IOP Conference Series: Materials Science and Engineering, 2017Co-Authors: Haocheng Wang, Gaofei Che, Maoqiong GongAbstract:Thermodynamic performance comparison of single-stage mixed-refrigerant Joule–Thomson cycle (MJTR) and pure refrigerant reverse Brayton cycle (RBC) for cooling 80 to 120 K temperature-distributed heat loads was conducted in this paper. Nitrogen under various liquefaction pressures was employed as the heat load. The research was conducted under nonideal conditions by exergy analysis methods. Exergy efficiency and volumetric cooling capacity are two main evaluation parameters. Exergy loss distribution in each Process of refrigeration cycle was also investigated. The exergy efficiency and volumetric cooling capacity of MJTR were obviously superior to RBC in 90 to 120 K temperature zone, but still inferior to RBC at 80 K. The performance degradation of MJTR was caused by two main reasons: The high fraction of neon resulted in large entropy generation and exergy loss in Throttling Process. Larger duty and WLMTD lead to larger exergy losses in recuperator.
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performance comparison of single stage mixed refrigerant joule thomson cycle and pure gas reverse brayton cycle at fixed temperatures from 80 to 180 k
International Journal of Refrigeration-revue Internationale Du Froid, 2017Co-Authors: Haocheng Wang, Gaofei Che, Y X Zhao, Xuezhi Dong, Hao Guo, Maoqiong GongAbstract:Abstract Performance comparison of single-stage mixed-refrigerant Joule–Thomson refrigeration cycle (MJTR) and pure-gas reverse Brayton cycle (RBC) at fixed-temperatures from 80 to 180 K was made in this paper. The simulation was mainly conducted under nonideal conditions with extrinsic irreversibilities. Exergy efficiency and volumetric cooling capacity are two main evaluation parameters. Exergy loss distributions along the cycles were analyzed. Under ideal conditions, RBC achieved the highest exergy efficiency at all temperatures, but lower volumetric cooling capacity than MJTR at middle-high temperatures. Under nonideal conditions, both the exergy efficiency and volumetric cooling capacity of MJTR were obviously superior to RBC from 100 to 180 K, but inferior to RBC at 80 K. Two reasons account for the sharp performance degradation of MJTR: The high fraction of neon resulted in large entropy generation and exergy loss in Throttling Process. Larger recuperator duty and WLMTD lead to larger losses in the recuperator.
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Performance comparison of single-stage mixed-refrigerant Joule–Thomson cycle and pure-gas reverse Brayton cycle at fixed-temperatures from 80 to 180 K
International Journal of Refrigeration, 2017Co-Authors: H.c. Wang, Y X Zhao, Hao Guo, Gaofei Chen, Dong Xuezhi, Maoqiong GongAbstract:Abstract Performance comparison of single-stage mixed-refrigerant Joule–Thomson refrigeration cycle (MJTR) and pure-gas reverse Brayton cycle (RBC) at fixed-temperatures from 80 to 180 K was made in this paper. The simulation was mainly conducted under nonideal conditions with extrinsic irreversibilities. Exergy efficiency and volumetric cooling capacity are two main evaluation parameters. Exergy loss distributions along the cycles were analyzed. Under ideal conditions, RBC achieved the highest exergy efficiency at all temperatures, but lower volumetric cooling capacity than MJTR at middle-high temperatures. Under nonideal conditions, both the exergy efficiency and volumetric cooling capacity of MJTR were obviously superior to RBC from 100 to 180 K, but inferior to RBC at 80 K. Two reasons account for the sharp performance degradation of MJTR: The high fraction of neon resulted in large entropy generation and exergy loss in Throttling Process. Larger recuperator duty and WLMTD lead to larger losses in the recuperator.
Angelo Algieri - One of the best experts on this subject based on the ideXlab platform.
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fluid dynamic investigation of innovative intake strategies for multivalve internal combustion engines
International Journal of Mechanical Sciences, 2017Co-Authors: Alessandra Nigro, Angelo Algieri, Carmine De Bartolo, Sergio BovaAbstract:Abstract The aim of the paper is to investigate the influence of novel opening strategies for intake valves on the permeability and in-cylinder flow of a multivalve spark-ignition internal combustion engine. Specifically, the deactivation of an intake valve and asymmetric valves lifts are analysed and compared to the standard symmetric valves opening. To this purpose, a computational fluid dynamic (CFD) analysis is performed by using a finite volume code and an experimental activity is done at a steady flow rig. The investigation is carried out for different intake strategies and engine load conditions and the comparison between CFD and experimental flow coefficients shows a good agreement. The results demonstrate that the proper combination of different valves strategies permits the effect of the Throttling Process at medium and low engine load to be minimised, improving the breathability of the intake system, and creating more organised and energised mean flow structures within the combustion chamber.
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Comparative analysis of the fluid dynamic efficiency of standard and alternative intake strategies for multivalve spark-ignition engines
International Journal of Engineering & Technology, 2013Co-Authors: Angelo AlgieriAbstract:The work aims at investigating the fluid dynamic performances of a multivalve spark-ignition engine and at evaluating the influence of the Throttling Process on the engine permeability. To this purpose, a production four-stroke internal combustion engine is analysed during the intake phase. The experimental characterisation is carried out at the steady flow rig in terms of dimensionless discharge and flow coefficients. The global investigation illustrates the noticeable effect of the valve lift on the engine head breathability. Furthermore, the experimental analysis demonstrates that the Throttling Process has a significant influence on the volumetric efficiency of the intake system and this effect increases with the valve lift. Finally, alternative strategies are studied in order to improve the engine fluid dynamic efficiency at partial loads. Specifically, the research shows that inlet valve deactivation and the adoption of asymmetric intake valve lifts assure an increase in head permeability.
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An Experimental Analysis of the Fluid Dynamic Efficiency of a Production Spark-Ignition Engine during the Intake and Exhaust Phase
ISRN Mechanical Engineering, 2011Co-Authors: Angelo AlgieriAbstract:The present work aims at analyzing the fluid dynamic efficiency of a four-stroke spark-ignition engine. Specifically, a production four-cylinder internal combustion engine has been investigated during the intake and exhaust phase. The experimental characterization has been carried out at the steady flow rig adopting the dimensionless flow and discharge coefficients. The analysis has highlighted the great influence of the valve lift on the volumetric efficiency of the intake and exhaust system. Furthermore, the global investigation has demonstrated that the throttle angle has a significant influence on the head permeability during the induction phase. Particularly, the Throttling Process effect increases with the valve lift. Finally, the work has shown that all experimental data can be correlated by a single curve if an opportune dimensionless plot is adopted.
Hao Guo - One of the best experts on this subject based on the ideXlab platform.
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performance comparison of single stage mixed refrigerant joule thomson cycle and pure gas reverse brayton cycle at fixed temperatures from 80 to 180 k
International Journal of Refrigeration-revue Internationale Du Froid, 2017Co-Authors: Haocheng Wang, Gaofei Che, Y X Zhao, Xuezhi Dong, Hao Guo, Maoqiong GongAbstract:Abstract Performance comparison of single-stage mixed-refrigerant Joule–Thomson refrigeration cycle (MJTR) and pure-gas reverse Brayton cycle (RBC) at fixed-temperatures from 80 to 180 K was made in this paper. The simulation was mainly conducted under nonideal conditions with extrinsic irreversibilities. Exergy efficiency and volumetric cooling capacity are two main evaluation parameters. Exergy loss distributions along the cycles were analyzed. Under ideal conditions, RBC achieved the highest exergy efficiency at all temperatures, but lower volumetric cooling capacity than MJTR at middle-high temperatures. Under nonideal conditions, both the exergy efficiency and volumetric cooling capacity of MJTR were obviously superior to RBC from 100 to 180 K, but inferior to RBC at 80 K. Two reasons account for the sharp performance degradation of MJTR: The high fraction of neon resulted in large entropy generation and exergy loss in Throttling Process. Larger recuperator duty and WLMTD lead to larger losses in the recuperator.
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Performance comparison of single-stage mixed-refrigerant Joule–Thomson cycle and pure-gas reverse Brayton cycle at fixed-temperatures from 80 to 180 K
International Journal of Refrigeration, 2017Co-Authors: H.c. Wang, Y X Zhao, Hao Guo, Gaofei Chen, Dong Xuezhi, Maoqiong GongAbstract:Abstract Performance comparison of single-stage mixed-refrigerant Joule–Thomson refrigeration cycle (MJTR) and pure-gas reverse Brayton cycle (RBC) at fixed-temperatures from 80 to 180 K was made in this paper. The simulation was mainly conducted under nonideal conditions with extrinsic irreversibilities. Exergy efficiency and volumetric cooling capacity are two main evaluation parameters. Exergy loss distributions along the cycles were analyzed. Under ideal conditions, RBC achieved the highest exergy efficiency at all temperatures, but lower volumetric cooling capacity than MJTR at middle-high temperatures. Under nonideal conditions, both the exergy efficiency and volumetric cooling capacity of MJTR were obviously superior to RBC from 100 to 180 K, but inferior to RBC at 80 K. Two reasons account for the sharp performance degradation of MJTR: The high fraction of neon resulted in large entropy generation and exergy loss in Throttling Process. Larger recuperator duty and WLMTD lead to larger losses in the recuperator.
Y X Zhao - One of the best experts on this subject based on the ideXlab platform.
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performance comparison of single stage mixed refrigerant joule thomson cycle and pure gas reverse brayton cycle at fixed temperatures from 80 to 180 k
International Journal of Refrigeration-revue Internationale Du Froid, 2017Co-Authors: Haocheng Wang, Gaofei Che, Y X Zhao, Xuezhi Dong, Hao Guo, Maoqiong GongAbstract:Abstract Performance comparison of single-stage mixed-refrigerant Joule–Thomson refrigeration cycle (MJTR) and pure-gas reverse Brayton cycle (RBC) at fixed-temperatures from 80 to 180 K was made in this paper. The simulation was mainly conducted under nonideal conditions with extrinsic irreversibilities. Exergy efficiency and volumetric cooling capacity are two main evaluation parameters. Exergy loss distributions along the cycles were analyzed. Under ideal conditions, RBC achieved the highest exergy efficiency at all temperatures, but lower volumetric cooling capacity than MJTR at middle-high temperatures. Under nonideal conditions, both the exergy efficiency and volumetric cooling capacity of MJTR were obviously superior to RBC from 100 to 180 K, but inferior to RBC at 80 K. Two reasons account for the sharp performance degradation of MJTR: The high fraction of neon resulted in large entropy generation and exergy loss in Throttling Process. Larger recuperator duty and WLMTD lead to larger losses in the recuperator.
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Performance comparison of single-stage mixed-refrigerant Joule–Thomson cycle and pure-gas reverse Brayton cycle at fixed-temperatures from 80 to 180 K
International Journal of Refrigeration, 2017Co-Authors: H.c. Wang, Y X Zhao, Hao Guo, Gaofei Chen, Dong Xuezhi, Maoqiong GongAbstract:Abstract Performance comparison of single-stage mixed-refrigerant Joule–Thomson refrigeration cycle (MJTR) and pure-gas reverse Brayton cycle (RBC) at fixed-temperatures from 80 to 180 K was made in this paper. The simulation was mainly conducted under nonideal conditions with extrinsic irreversibilities. Exergy efficiency and volumetric cooling capacity are two main evaluation parameters. Exergy loss distributions along the cycles were analyzed. Under ideal conditions, RBC achieved the highest exergy efficiency at all temperatures, but lower volumetric cooling capacity than MJTR at middle-high temperatures. Under nonideal conditions, both the exergy efficiency and volumetric cooling capacity of MJTR were obviously superior to RBC from 100 to 180 K, but inferior to RBC at 80 K. Two reasons account for the sharp performance degradation of MJTR: The high fraction of neon resulted in large entropy generation and exergy loss in Throttling Process. Larger recuperator duty and WLMTD lead to larger losses in the recuperator.
Ian K Smith - One of the best experts on this subject based on the ideXlab platform.
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numerical simulation of combined screw compressor expander machines for use in high pressure refrigeration systems
Simulation Modelling Practice and Theory, 2006Co-Authors: Ahmed Kovacevic, Nikola Stosic, Ian K SmithAbstract:Recent interest in natural refrigerants has created a new impetus for studies of CO2 as a working fluid in vapour compression systems for refrigeration and air conditioning. Two major drawbacks to its use are the very high pressure differences required across the compressor and the large efficiency losses associated with the Throttling Process in the refrigeration cycle. It is shown how these disadvantages can be minimised by the use of a screw machine both to compress the gas and use the expansion Process to recover power. Both these functions can be performed simultaneously, using only one pair of rotors, in a configuration that partially balances out the forces induced by the pressure difference and hence, reduces the bearing loads to an acceptable level. A further feature is the use of rotors, which seal on both contacting surfaces so that the same profile may be used for the expander and the compressor sections. This enables the rotors performing both these functions to be machined or ground in the same cutting operation and then separated by machining a parting slot in them. Computational Continuum Mechanics comprising both, fluid flow and structural analysis is used in this paper for the investigation of fluid-solid interaction in such machines.
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Numerical simulation of combined screw compressor–expander machines for use in high pressure refrigeration systems
Simulation Modelling Practice and Theory, 2006Co-Authors: Ahmed Kovacevic, Nikola Stosic, Ian K SmithAbstract:Recent interest in natural refrigerants has created a new impetus for studies of CO2 as a working fluid in vapour compression systems for refrigeration and air conditioning. Two major drawbacks to its use are the very high pressure differences required across the compressor and the large efficiency losses associated with the Throttling Process in the refrigeration cycle. It is shown how these disadvantages can be minimised by the use of a screw machine both to compress the gas and use the expansion Process to recover power. Both these functions can be performed simultaneously, using only one pair of rotors, in a configuration that partially balances out the forces induced by the pressure difference and hence, reduces the bearing loads to an acceptable level. A further feature is the use of rotors, which seal on both contacting surfaces so that the same profile may be used for the expander and the compressor sections. This enables the rotors performing both these functions to be machined or ground in the same cutting operation and then separated by machining a parting slot in them. Computational Continuum Mechanics comprising both, fluid flow and structural analysis is used in this paper for the investigation of fluid-solid interaction in such machines.
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a twin screw combined compressor and expander for co2 refrigeration systems
2002Co-Authors: Nikola Stosic, Ian K Smith, Ahmed KovacevicAbstract:Recent interest in natural refrigerants has created a new impetus for studies of CO2 as a working fluid in vapour compression systems for refrigeration and air conditioning. Two major drawbacks to its use are the very high pressure differences required across the compressor and the large efficiency losses associated with the Throttling Process. To overcome the throttle losses, a number of proposals have been made for various types of positive displacement machine, mainly of the vane type, which combine compression with some recovery of work from the expansion Process. However, how well they operate with high pressure differences across the vanes has not been confirmed. For many years, the authors have been investigating the use of twin screw machines to fulfil both the expansion and compression Processes when using more conventional halocarbon refrigerants. These have many potential advantages over other types of positive displacement machine. Unfortunately, when applied to CO2 the huge bearing forces associated with the pressure distribution within them have hitherto made them appear to be unsuitable. In this paper, it is shown how the rotor forces created by the compression and expansion Processes can be partially balanced in order to eliminate the axial forces and reduce the radial bearing forces. The disadvantages of twin screw compressors for such high pressure applications are thereby reduced. The balanced rotor concept is also applicable to vapour compression systems using more conventional refrigerants and even for high pressure gas compression.
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Twin screw machines to replace throttle valves in refrigeration systems
Strojniški vestnik, 2001Co-Authors: Ian K Smith, Nikola Stosic, Ahmed KovacevicAbstract:As the component efficiencies of vapour compression refrigeration systems approach their upper limits, the losses due to Throttling within the cycle become more significant, especially with the newer refrigerants. Two-phase expanders to replace the throttle valve and recover power from the loss of the Throttling Process then become more attractive. The use of twin screw machines for this purpose is considered with the power so recovered to be used in a variety of ways. These include direct drive of the main compressor, an electric generator, or another compressor or direct recompression of part of the vapour formed during expansion within the same pair of rotors.
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Development of a Twin Screw Expressor as a Throttle Valve Replacement for Water-Cooled Chillers
2000Co-Authors: J. J. Brasz, Ian K Smith, Nikola StosicAbstract:An introductory report is given on a novel means of replacing the Throttling Process in vapour compression systems. Power is recovered from the two-phase expansion Process and used directly to recompress a portion of the vapour formed during the expansion. Both the expansion and recompression Processes are carried out in a twin screw machine with only one pair of rotors. These rotate, without the need for timing gear, in a Process-lubricated, totally sealed unit which the authors have called an “expressor”. First test results indicate that the overall expansion-compression efficiency of the expressor is of the order of 55%. This corresponds roughly to 70% expansion efficiency and 80% compression efficiency. The simplicity of the expressor design, together with its promising performance give clear indications that it should be a highly cost effective component in large commercial chiller systems.
