Hydrogen energy,with its abundant reserves,green and low-carbon characteristic,high energy density,diverse sources,and wide applications,is gradually becoming an important carrier in the global energy transformation a...Hydrogen energy,with its abundant reserves,green and low-carbon characteristic,high energy density,diverse sources,and wide applications,is gradually becoming an important carrier in the global energy transformation and development.In this paper,the off-grid wind power hydrogen production system is considered as the research object,and the operating characteristics of a proton exchange membrane(PEM)electrolysis cell,including underload,overload,variable load,and start-stop are analyzed.On this basis,the characteristic extraction of wind power output data after noise reduction is carried out,and then the self-organizing mapping neural network algorithm is used for clustering to extract typical wind power output scenarios and perform weight distribution based on the statistical probability.The trend and fluctuation components are superimposed to generate the typical operating conditions of an off-grid PEM electrolytic hydrogen production system.The historical output data of an actual wind farm are used for the case study,and the results confirm the feasibility of the method proposed in this study for obtaining the typical conditions of off-grid wind power hydrogen production.The results provide a basis for studying the dynamic operation characteristics of PEM electrolytic hydrogen production systems,and the performance degradation mechanism of PEM electrolysis cells under fluctuating inputs.展开更多
In this study,a three-dimensional numerical investigation was conducted on the front and rear fans of a three-bypass variable cycle engine under various speeds and internal bypass conditions.The impact of internal byp...In this study,a three-dimensional numerical investigation was conducted on the front and rear fans of a three-bypass variable cycle engine under various speeds and internal bypass conditions.The impact of internal bypass conditions and speeds on the matching characteristics of the front and rear fans,as well as the factors limiting the variation of bypass ratio,are summarized.The findings reveal that for near stall,design point,and near choke internal bypass conditions,the operating point of the front fan tends to move towards near-stall while that of the rear fan moves towards near-choke when increasing external bypass back pressure.At design speed,external bypass blockage is identified as a limiting factor for increasing the bypass ratio at the internal bypass design point.Additionally,blockage caused by a significant amount of low-energy fluid at the suction surface of the rear fan stator leads to rear fan stall which limits further increase in bypass ratio at external bypass near stall condition.Similarly,leakage flow overflow passage at the top section of first stage rotor blade in front fan results in front fan stall,which restricts decrease in bypass ratio at internal bypass near stall condition.As corrected speed decreases,there is an upper-left shift observed in the curve depicting variation in relative back pressure with respect to change in bypass ratio due to the phenomenon "pre-surge and post-choke".This indicates increased air flow into external bypass resulting in higher values for lower speeds.Furthermore,limitation on further increase in bypass ratio at external bypass near stall condition with decreasing speed can be attributed to transition from rear fan stall to external bypass blockage.展开更多
基金supported by the National Key Research and Development Program of China(Program Number 2021YFB4000100)the Beijing Postdoctoral Research Foundation(Grant Number 2023-ZZ-63).
文摘Hydrogen energy,with its abundant reserves,green and low-carbon characteristic,high energy density,diverse sources,and wide applications,is gradually becoming an important carrier in the global energy transformation and development.In this paper,the off-grid wind power hydrogen production system is considered as the research object,and the operating characteristics of a proton exchange membrane(PEM)electrolysis cell,including underload,overload,variable load,and start-stop are analyzed.On this basis,the characteristic extraction of wind power output data after noise reduction is carried out,and then the self-organizing mapping neural network algorithm is used for clustering to extract typical wind power output scenarios and perform weight distribution based on the statistical probability.The trend and fluctuation components are superimposed to generate the typical operating conditions of an off-grid PEM electrolytic hydrogen production system.The historical output data of an actual wind farm are used for the case study,and the results confirm the feasibility of the method proposed in this study for obtaining the typical conditions of off-grid wind power hydrogen production.The results provide a basis for studying the dynamic operation characteristics of PEM electrolytic hydrogen production systems,and the performance degradation mechanism of PEM electrolysis cells under fluctuating inputs.
基金financially supported by the National Science and Technology Major Project (No. J2019-Ⅱ-0004-0024)Youth Innovation Promotion Association CAS (No.202043)。
文摘In this study,a three-dimensional numerical investigation was conducted on the front and rear fans of a three-bypass variable cycle engine under various speeds and internal bypass conditions.The impact of internal bypass conditions and speeds on the matching characteristics of the front and rear fans,as well as the factors limiting the variation of bypass ratio,are summarized.The findings reveal that for near stall,design point,and near choke internal bypass conditions,the operating point of the front fan tends to move towards near-stall while that of the rear fan moves towards near-choke when increasing external bypass back pressure.At design speed,external bypass blockage is identified as a limiting factor for increasing the bypass ratio at the internal bypass design point.Additionally,blockage caused by a significant amount of low-energy fluid at the suction surface of the rear fan stator leads to rear fan stall which limits further increase in bypass ratio at external bypass near stall condition.Similarly,leakage flow overflow passage at the top section of first stage rotor blade in front fan results in front fan stall,which restricts decrease in bypass ratio at internal bypass near stall condition.As corrected speed decreases,there is an upper-left shift observed in the curve depicting variation in relative back pressure with respect to change in bypass ratio due to the phenomenon "pre-surge and post-choke".This indicates increased air flow into external bypass resulting in higher values for lower speeds.Furthermore,limitation on further increase in bypass ratio at external bypass near stall condition with decreasing speed can be attributed to transition from rear fan stall to external bypass blockage.
