In this paper,exergy analysis method is developed to assess a Rankine cycle system,by using supercritical CO2 as working fluid and powered by solar energy.The proposed system consists of evacuated solar collectors,thr...In this paper,exergy analysis method is developed to assess a Rankine cycle system,by using supercritical CO2 as working fluid and powered by solar energy.The proposed system consists of evacuated solar collectors,throttling valve,high-temperature heat exchanger,low-temperature heat exchanger,and feed pump.The system is designed for utilize evacuated solar collectors to convert solar energy into mechanical energy and hence electricity.In order to investigate and estimate exergy performance of this system,the energy,entropy,exergy balances are developed for the components.The exergy destructions and exergy efficiency values of the system components are also determined.The results indicate that solar collector and high temperature heat exchanger which have low exergy efficiencies contribute the largest share to system irreversibility and should be the optimization design focus to improve system exergy effectiveness.Further,exergy analysis is a useful tool in this regard as it permits the performance of each process to be assessed and losses to be quantified.Exergy analysis results can be used in design,optimization,and improvement efforts.展开更多
A novel heat treatment process,stepping quenching and partitioning(S-Q-P),has been developed to manipulate microstructure and mechanical properties of steels.Based on incomplete partitioning of carbon from martensite ...A novel heat treatment process,stepping quenching and partitioning(S-Q-P),has been developed to manipulate microstructure and mechanical properties of steels.Based on incomplete partitioning of carbon from martensite to austenite,volume fraction and distribution of the retained austenite resulting from the following quenching of the steels could be effectively controlled,and then the synthesized mechanical properties of the steels would be improved.In this paper,20SiMn2MoVA steel was treated with conventional quenching-tempering(Q-T),currently prevailing quenching-partitioning(Q-P) and S-Q-P processes,respectively.The results indicated that the volume fraction of the retained austenite of the steel treated by Q-P and S-Q-P processes increased significantly that resulted in the increase of ductility and decrease of strength.The product of strength and ductility of the steel treated by S-Q-P process reached 23.7GPa%,that was increased by about 13% and 7% compared with that after Q-T and Q-P processes,respectively.Compared with the great improvement of the synthesized mechanical property obtained by S-Q-P process with another steel 35SiMn,there would be some factors that deteriorated the effect of S-Q-P process on 20SiMn2MoVA steel.It was found by microstructural testing that the carbide forming elements V and Mo in the steel led to precipitation of carbides during partitioning period and lack of carbon in austenite.As a result,less austenite would remain after final quenching and mechanical properties of the steel would be influenced.The results would be beneficial for understanding the principle of S-Q-P process and improving the design of the S-Q-P steel compositions.展开更多
基金The support of the National Natural Science Founda-tion of China (50976002) is gratefully acknowledged
文摘In this paper,exergy analysis method is developed to assess a Rankine cycle system,by using supercritical CO2 as working fluid and powered by solar energy.The proposed system consists of evacuated solar collectors,throttling valve,high-temperature heat exchanger,low-temperature heat exchanger,and feed pump.The system is designed for utilize evacuated solar collectors to convert solar energy into mechanical energy and hence electricity.In order to investigate and estimate exergy performance of this system,the energy,entropy,exergy balances are developed for the components.The exergy destructions and exergy efficiency values of the system components are also determined.The results indicate that solar collector and high temperature heat exchanger which have low exergy efficiencies contribute the largest share to system irreversibility and should be the optimization design focus to improve system exergy effectiveness.Further,exergy analysis is a useful tool in this regard as it permits the performance of each process to be assessed and losses to be quantified.Exergy analysis results can be used in design,optimization,and improvement efforts.
基金supported by the National Basic Research Program of China("973" Program) (Grant No. 2010CB630805)
文摘A novel heat treatment process,stepping quenching and partitioning(S-Q-P),has been developed to manipulate microstructure and mechanical properties of steels.Based on incomplete partitioning of carbon from martensite to austenite,volume fraction and distribution of the retained austenite resulting from the following quenching of the steels could be effectively controlled,and then the synthesized mechanical properties of the steels would be improved.In this paper,20SiMn2MoVA steel was treated with conventional quenching-tempering(Q-T),currently prevailing quenching-partitioning(Q-P) and S-Q-P processes,respectively.The results indicated that the volume fraction of the retained austenite of the steel treated by Q-P and S-Q-P processes increased significantly that resulted in the increase of ductility and decrease of strength.The product of strength and ductility of the steel treated by S-Q-P process reached 23.7GPa%,that was increased by about 13% and 7% compared with that after Q-T and Q-P processes,respectively.Compared with the great improvement of the synthesized mechanical property obtained by S-Q-P process with another steel 35SiMn,there would be some factors that deteriorated the effect of S-Q-P process on 20SiMn2MoVA steel.It was found by microstructural testing that the carbide forming elements V and Mo in the steel led to precipitation of carbides during partitioning period and lack of carbon in austenite.As a result,less austenite would remain after final quenching and mechanical properties of the steel would be influenced.The results would be beneficial for understanding the principle of S-Q-P process and improving the design of the S-Q-P steel compositions.
