Vanadium flow battery(VFB)is one of the most promising energy storage technologies because of its superior safety,reliability and cycle life,but the poor electrochemical performance at high cur-rent density limits its...Vanadium flow battery(VFB)is one of the most promising energy storage technologies because of its superior safety,reliability and cycle life,but the poor electrochemical performance at high cur-rent density limits its commercial application.Herein,an advanced design of the dual-gradient carbon nanofibers/graphite felt(DG-CNFs/GF)composite electrode is firstly proposed for the next-generation VFB with high power density.Specifically,there is a macro gradient distribution of CNFs along the thickness direction of the electrode,meanwhile a micro gradient distribution of CNFs is also existed along the ra-dial direction of a single fiber,and both the macro and micro gradient structure are verified through the physicochemical characterizations.In addition,the DG-CNFs/GF with a dual-gradient structure exhibits an excellent electrocatalytic activity and a fast mass transfer characteristic.It is worth noting that the energy conversion efficiencies,cycling stability in addition to power density of VFB with DG-CNFs/GF are much better than those with commercial GF,which make the dual-gradient DG-CNFs/GF to be a promis-ing alternative.Most importantly,the accomplishment of this work will provide a promising development direction of the highly efficient electrode for the next-generation VFB with high power density.展开更多
To ensure safe drilling with narrow pressure margins in deepwater, a new deepwater dual-gradient drilling method based on downhole separation was designed. A laboratory experiment was conducted to verify the effective...To ensure safe drilling with narrow pressure margins in deepwater, a new deepwater dual-gradient drilling method based on downhole separation was designed. A laboratory experiment was conducted to verify the effectiveness of downhole separation and the feasibility of realizing dual-gradient in wellbore. The calculation of dynamic wellbore pressure during drilling was conducted. Then, an optimization model for drilling parameters was established for this drilling method, including separator position, separation efficiency, injection volume fraction, density of drilling fluid, wellhead back pressure and displacement. The optimization of drilling parameters under different control parameters and different narrow safe pressure margins is analyzed by case study. The optimization results indicate that the wellbore pressure profile can be optimized to adapt to the narrow pressure margins and achieve greater drilling depth. By using the optimization model, a smaller bottom-hole pressure difference can be obtained, which can increase the rate of penetration(ROP) and protect reservoirs. The dynamic wellbore pressure has been kept within safe pressure margins during optimization process, effectively avoiding the complicated underground situations caused by improper wellbore pressure.展开更多
The rational design of a 3D scaffold with optimized electrical conductivity,sodiophilicity,and sufficient internal space is crucial for suppressing the growth of Na dendrites and accommodating the large volume changes...The rational design of a 3D scaffold with optimized electrical conductivity,sodiophilicity,and sufficient internal space is crucial for suppressing the growth of Na dendrites and accommodating the large volume changes of Na metal anodes during the plating/stripping process.Nevertheless,the uniform conductivity and sodiophilicity of conventional scaffolds often lead to Na metal deposition on the top of the scaffold,thereby hindering the complete functional capabilities of the scaffold.To tackle this challenge,we developed a novel imprinted dual-gradient 3D network skeleton that boasts gradients in both sodiophilicity and conductivity.Both theoretical and experimental analyses indicate that Na metal prefers to nucleate and deposit dendrite-free from the bottom of the 3D skeleton due to its superior conductivity and sodiophilicity.This dual-gradient design enables the electrode to achieve low nucleation overpotential of 11 mV and sustain stable operation for 1900 h at 1.5 m A cm^(-2) /1.5 mAh cm^(-2) and1000 h at 20 mA cm^(-2) /20 mAh cm^(-2) ,far superior to the gradientless electrode.When paired with Na_(3)V_(2) (PO_(4))_(3) cathode,the full cell retains a capacity of 67.6 mAh g^(-1) after 1000 stable cycles with a capacity retention rate of 82.4%at a rate of 10 C.This advanced skeleton structure design is poised to advance the development of high-energy-density alkali metal batteries.展开更多
With the growing demand for offshore energy,deepwater drilling has become a vital technology in petroleum engineering.However,conventional drilling systems often face limitations such as delayed bottomhole pressure re...With the growing demand for offshore energy,deepwater drilling has become a vital technology in petroleum engineering.However,conventional drilling systems often face limitations such as delayed bottomhole pressure response and low control precision,particularly under narrow pressure window and complex formation conditions.To address these challenges,Dual-layer Pipe dual-gradient drilling(DGD)technology has been introduced,utilizing a dual-pipe structure and downhole lift pumps to extend the pressure control range.Despite these advantages,current DGD systems lack fast and precise bottomhole pressure control due to their reliance on indirect flow-based methods.This study proposes a bottomhole pressure control method based on backpressure regulation using a hybrid fuzzy-PID control strategy.A dynamic pressure calculation model is developed for the Dual-layer Pipe DGD system,incorporating coupling among choke valve opening,surface backpressure,and bottomhole pressure.The fuzzy-PID controller adjusts valve operation in real-time based on pressure deviation and its rate of change,improving response speed and control accuracy.Simulink-based simulations demonstrate that the proposed system achieves rapid pressure regulation with an overshoot below 5%and steady-state error under 0.12%.Compared to conventional PID control,the fuzzy-PID system shows superior adaptability to pressure variations.This research enhances the theoretical foundation of backpressure control in deepwater DGD operations and provides a practical approach for improving safety and efficiency in complex drilling environments.展开更多
基金This work was financially supported by the National Natural Science Foundation of China Youth Fund(No.21703263)Open project of State Key Laboratory of Heavy Oil Processing in China University of Petroleum(No.Y7F1911191).
文摘Vanadium flow battery(VFB)is one of the most promising energy storage technologies because of its superior safety,reliability and cycle life,but the poor electrochemical performance at high cur-rent density limits its commercial application.Herein,an advanced design of the dual-gradient carbon nanofibers/graphite felt(DG-CNFs/GF)composite electrode is firstly proposed for the next-generation VFB with high power density.Specifically,there is a macro gradient distribution of CNFs along the thickness direction of the electrode,meanwhile a micro gradient distribution of CNFs is also existed along the ra-dial direction of a single fiber,and both the macro and micro gradient structure are verified through the physicochemical characterizations.In addition,the DG-CNFs/GF with a dual-gradient structure exhibits an excellent electrocatalytic activity and a fast mass transfer characteristic.It is worth noting that the energy conversion efficiencies,cycling stability in addition to power density of VFB with DG-CNFs/GF are much better than those with commercial GF,which make the dual-gradient DG-CNFs/GF to be a promis-ing alternative.Most importantly,the accomplishment of this work will provide a promising development direction of the highly efficient electrode for the next-generation VFB with high power density.
基金Supported by the Key Program of National Natural Science Foundation of China(51734010)
文摘To ensure safe drilling with narrow pressure margins in deepwater, a new deepwater dual-gradient drilling method based on downhole separation was designed. A laboratory experiment was conducted to verify the effectiveness of downhole separation and the feasibility of realizing dual-gradient in wellbore. The calculation of dynamic wellbore pressure during drilling was conducted. Then, an optimization model for drilling parameters was established for this drilling method, including separator position, separation efficiency, injection volume fraction, density of drilling fluid, wellhead back pressure and displacement. The optimization of drilling parameters under different control parameters and different narrow safe pressure margins is analyzed by case study. The optimization results indicate that the wellbore pressure profile can be optimized to adapt to the narrow pressure margins and achieve greater drilling depth. By using the optimization model, a smaller bottom-hole pressure difference can be obtained, which can increase the rate of penetration(ROP) and protect reservoirs. The dynamic wellbore pressure has been kept within safe pressure margins during optimization process, effectively avoiding the complicated underground situations caused by improper wellbore pressure.
基金supported by the National Natural Science Foundation of China(22209140,52202286)the Qingchuang Technology Support Program of the University in Shandong Province(2024KJH080)+6 种基金the Natural Science Foundation of Shandong Province(ZR2022QE059,ZR2024MB153)the Shandong Laboratory of Advanced Materials and Green Manufacturing at Yantai(Yantai)(AMGM2023A08)the Natural Science Foundation of Zhejiang Province(LQ23B030011,LY24B030006)the Scientific Research Fund of Zhejiang Provincial Education Department(Y202148249)the Science and Technology Plan Project of Wenzhou Municipality(ZG2024055,ZG2022032)the Wenzhou Association for Science and Technology Innovation Program(NLTS2024-013)the Natural Science Foundation of Guangdong Province-Youth Promotion Project(2024A1515030173)。
文摘The rational design of a 3D scaffold with optimized electrical conductivity,sodiophilicity,and sufficient internal space is crucial for suppressing the growth of Na dendrites and accommodating the large volume changes of Na metal anodes during the plating/stripping process.Nevertheless,the uniform conductivity and sodiophilicity of conventional scaffolds often lead to Na metal deposition on the top of the scaffold,thereby hindering the complete functional capabilities of the scaffold.To tackle this challenge,we developed a novel imprinted dual-gradient 3D network skeleton that boasts gradients in both sodiophilicity and conductivity.Both theoretical and experimental analyses indicate that Na metal prefers to nucleate and deposit dendrite-free from the bottom of the 3D skeleton due to its superior conductivity and sodiophilicity.This dual-gradient design enables the electrode to achieve low nucleation overpotential of 11 mV and sustain stable operation for 1900 h at 1.5 m A cm^(-2) /1.5 mAh cm^(-2) and1000 h at 20 mA cm^(-2) /20 mAh cm^(-2) ,far superior to the gradientless electrode.When paired with Na_(3)V_(2) (PO_(4))_(3) cathode,the full cell retains a capacity of 67.6 mAh g^(-1) after 1000 stable cycles with a capacity retention rate of 82.4%at a rate of 10 C.This advanced skeleton structure design is poised to advance the development of high-energy-density alkali metal batteries.
基金the Sichuan Provincial Key R&D Program(Regional Innovation Coop-eration Project 2025YFHZ0306)Open Fund(PLN 2022-46)of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation(Southwest Petroleum University)Special Support for Sichuan Postdoctoral Research Projects.
文摘With the growing demand for offshore energy,deepwater drilling has become a vital technology in petroleum engineering.However,conventional drilling systems often face limitations such as delayed bottomhole pressure response and low control precision,particularly under narrow pressure window and complex formation conditions.To address these challenges,Dual-layer Pipe dual-gradient drilling(DGD)technology has been introduced,utilizing a dual-pipe structure and downhole lift pumps to extend the pressure control range.Despite these advantages,current DGD systems lack fast and precise bottomhole pressure control due to their reliance on indirect flow-based methods.This study proposes a bottomhole pressure control method based on backpressure regulation using a hybrid fuzzy-PID control strategy.A dynamic pressure calculation model is developed for the Dual-layer Pipe DGD system,incorporating coupling among choke valve opening,surface backpressure,and bottomhole pressure.The fuzzy-PID controller adjusts valve operation in real-time based on pressure deviation and its rate of change,improving response speed and control accuracy.Simulink-based simulations demonstrate that the proposed system achieves rapid pressure regulation with an overshoot below 5%and steady-state error under 0.12%.Compared to conventional PID control,the fuzzy-PID system shows superior adaptability to pressure variations.This research enhances the theoretical foundation of backpressure control in deepwater DGD operations and provides a practical approach for improving safety and efficiency in complex drilling environments.
