A coupled CFD-DEM method is used to simulate the formation process of fracture plugging zone.A photo-elastic system characterizing mesoscale force chain network developed by our own is used to model the pressure evolu...A coupled CFD-DEM method is used to simulate the formation process of fracture plugging zone.A photo-elastic system characterizing mesoscale force chain network developed by our own is used to model the pressure evolution in fracture plugging zone to reveal the evolution mechanism of the structure of fracture plugging zone.A theoretical basis is provided for improving the lost circulation control effect in fractured reservoirs and novel methods are proposed for selecting loss control materials and designing loss control formula.CFD-DEM simulation results show that bridging probability is the key factor determining the formation of fracture plugging zone and fracture plugging efficiency.Critical and absolute bridging concentrations are proposed as the key indexes for loss control formula design.With the increase of absolute bridging concentration,the governing factor of bridging is changed from material grain size to the combination of material grain size and friction force.Results of photo-elastic experiments show that mesoscale force chain network is the intrinsic factor affecting the evolution of pressure exerting on the fracture plugging zone and determines the macroscopic strength of fracture plugging zone.Performance parameters of loss control material affect the force chain network structure and the ratio of stronger force chain,and further impact the stability and strength of fracture plugging zone.Based on the study results,the loss control formula is optimized and new-type loss control material is designed.Laboratory experiments results show that the fracture plugging efficiency and strength is effectively improved.展开更多
Quantum cascade lasers(QCLs)are unipolar quantum devices based on inter-sub-band transitions.They break the electron-hole recombination mechanism in traditional semiconductor lasers,overcome the long-lasting bottlenec...Quantum cascade lasers(QCLs)are unipolar quantum devices based on inter-sub-band transitions.They break the electron-hole recombination mechanism in traditional semiconductor lasers,overcome the long-lasting bottleneck which is that the emission wavelength of semiconductor laser is completely dependent on the bandgap of semiconductor materials.Therefore,their emission wavelength is able to cover the mid-infrared(mid-IR)range and the"Terahertz gap"that is previously inaccessible by any other semiconductor lasers.After thirty years development,QCLs have become the most promising light source in the mid-IR and THz regime.In this paper,we are going to present the strategies and methodologies to achieve high-power,high-wall-plug-efficiency(WPE)QCLs with high-brightness in room temperature continuous-wave(cw)operation at 3-300μm.We will also review the recent breakthroughs in QCL community,especially the high-power,high WPE intersubband lasers in room temperature cw operation.展开更多
With an n-A1GaN （4 nm）/GaN （4 nm） superlattice （SL） inserted between an n-GaN and an InGaN/GaN multiquantum well active layer, the efficiency droop of GaN-based LEDs has been improved. When the injection current...With an n-A1GaN （4 nm）/GaN （4 nm） superlattice （SL） inserted between an n-GaN and an InGaN/GaN multiquantum well active layer, the efficiency droop of GaN-based LEDs has been improved. When the injection current is lower than 100 mA, the lumen efficiency of the LED with an n-AlGaN/GaN SL is relatively small compared to that without an n-AlGaN/GaN SL. However, as the injection current increases more than 100 mA, the lumen efficiency of the LED with an n-A1GaN/GaN SL surpasses that of an LED without an n-AlGaN/GaN SL. The wall plug efficiency of an LED has the same trend as lumen efficiency. The improvement of the efficiency droop of LEDs with n-AIGaN/GaN SLs can be attributed to a decrease in electron leakage due to the enhanced current spreading ability and electron blocking effect at high current densities. The reverse current of LEDs at -5 V reverse voltage decreases from 0.2568029 to 0.0070543 μA, and the electro-static discharge （ESD） pass yield of an LED at human body mode （HBM）-ESD impulses of 2000 V increases from 60% to 90%.展开更多
基金Supported by the National Natural Science Foundation of China(51604236)Open Fund of the State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation(PLN201913)+1 种基金Science and Technology Planning Project of the Sichuan Province,China(2018JY0436)Sichuan Youth Science and Technology Innovation Research Team Project for Unconventional Oil and Gas Reservoir Protection(2016TD0016)。
文摘A coupled CFD-DEM method is used to simulate the formation process of fracture plugging zone.A photo-elastic system characterizing mesoscale force chain network developed by our own is used to model the pressure evolution in fracture plugging zone to reveal the evolution mechanism of the structure of fracture plugging zone.A theoretical basis is provided for improving the lost circulation control effect in fractured reservoirs and novel methods are proposed for selecting loss control materials and designing loss control formula.CFD-DEM simulation results show that bridging probability is the key factor determining the formation of fracture plugging zone and fracture plugging efficiency.Critical and absolute bridging concentrations are proposed as the key indexes for loss control formula design.With the increase of absolute bridging concentration,the governing factor of bridging is changed from material grain size to the combination of material grain size and friction force.Results of photo-elastic experiments show that mesoscale force chain network is the intrinsic factor affecting the evolution of pressure exerting on the fracture plugging zone and determines the macroscopic strength of fracture plugging zone.Performance parameters of loss control material affect the force chain network structure and the ratio of stronger force chain,and further impact the stability and strength of fracture plugging zone.Based on the study results,the loss control formula is optimized and new-type loss control material is designed.Laboratory experiments results show that the fracture plugging efficiency and strength is effectively improved.
基金support of the Walter P.Murphy Chair Professorship at the McCormick School of Engineering,Northwestern UniversityCo-author Professor Feihu Wang formerly a Research Assistant Professor at CQD/Northwestern University and currently based in China gratefully acknowledges the support of Guangdong Basic and Applied Basic Research Foundation(2023A1515012793,2024B1515020117)。
文摘Quantum cascade lasers(QCLs)are unipolar quantum devices based on inter-sub-band transitions.They break the electron-hole recombination mechanism in traditional semiconductor lasers,overcome the long-lasting bottleneck which is that the emission wavelength of semiconductor laser is completely dependent on the bandgap of semiconductor materials.Therefore,their emission wavelength is able to cover the mid-infrared(mid-IR)range and the"Terahertz gap"that is previously inaccessible by any other semiconductor lasers.After thirty years development,QCLs have become the most promising light source in the mid-IR and THz regime.In this paper,we are going to present the strategies and methodologies to achieve high-power,high-wall-plug-efficiency(WPE)QCLs with high-brightness in room temperature continuous-wave(cw)operation at 3-300μm.We will also review the recent breakthroughs in QCL community,especially the high-power,high WPE intersubband lasers in room temperature cw operation.
文摘With an n-A1GaN （4 nm）/GaN （4 nm） superlattice （SL） inserted between an n-GaN and an InGaN/GaN multiquantum well active layer, the efficiency droop of GaN-based LEDs has been improved. When the injection current is lower than 100 mA, the lumen efficiency of the LED with an n-AlGaN/GaN SL is relatively small compared to that without an n-AlGaN/GaN SL. However, as the injection current increases more than 100 mA, the lumen efficiency of the LED with an n-A1GaN/GaN SL surpasses that of an LED without an n-AlGaN/GaN SL. The wall plug efficiency of an LED has the same trend as lumen efficiency. The improvement of the efficiency droop of LEDs with n-AIGaN/GaN SLs can be attributed to a decrease in electron leakage due to the enhanced current spreading ability and electron blocking effect at high current densities. The reverse current of LEDs at -5 V reverse voltage decreases from 0.2568029 to 0.0070543 μA, and the electro-static discharge （ESD） pass yield of an LED at human body mode （HBM）-ESD impulses of 2000 V increases from 60% to 90%.
