Liquid nitrogen has shown excellent performances as a good fracturing medium in the extraction of unconventional natural gas,and its application in coalbed methane extraction is currently a research hotspot.This study...Liquid nitrogen has shown excellent performances as a good fracturing medium in the extraction of unconventional natural gas,and its application in coalbed methane extraction is currently a research hotspot.This study focuses on the acoustic emission properties of coal specimens treated utilizing liquid nitrogen with varying initial temperatures in a three-point bending environment.Through examination of the load-displacement curves of the considered coal samples,their mechanical properties are also revealed for different initial temperatures and cycling frequencies.The findings demonstrate a gradual decline in the maximum load capacity of coal rock as the temperature rises.Similarly,when subjected to the same temperature,an escalation in the cycling frequency leads to a reduction in the peak load of coal rock.This suggests that both temperature and cycling frequency exert a notable impact on the fracturing efficacy of liquid nitrogen.Freeze-thaw cycling treatments and exposure to high-temperature conditions can activate preexisting damage in the coal rock,and,accordingly,influence its mechanical properties.In particular,throughout the progressive loading of coal rock samples,the failure mechanisms are predominantly characterized by the occurrence of tensile cracks,succeeded by the development,spread,and fracture of shear fissures.展开更多
OLED(Organic Light-Emitting Diode)屏幕COF(Chip on Film)连接过渡区的金属层在模组弯折阶段和可靠性验证阶段容易发生断裂,导致屏幕显示异常。本文采用试验设计(Design of Experiment,DOE)方法,以弯折成型状态和可靠性状态下的金属...OLED(Organic Light-Emitting Diode)屏幕COF(Chip on Film)连接过渡区的金属层在模组弯折阶段和可靠性验证阶段容易发生断裂,导致屏幕显示异常。本文采用试验设计(Design of Experiment,DOE)方法,以弯折成型状态和可靠性状态下的金属层应力最小作为试验指标,以泡棉厚度、泡棉偏移、金属包覆层(Metal Cover Layer,MCL)厚度和U型膜偏移作为影响因子,设计L9(34)正交试验方案,使用有限元方法对9组试验方案进行数值模拟和分析,并进行弯折成型和可靠性状态下的试验验证,最终获得了最优组合方案。有限元方法和试验结果表明,U型膜贴附偏移量对COF区的金属层弯折应力的影响最大,其次是泡棉厚度,再次是MCL厚度和泡棉贴附偏移量。最优组合方案在弯折成型和可靠性状态下皆具有最小的金属层应力,其值分别为57 MPa和523 MPa。最优组合方案的弯折成型和可靠性试验达到了100%的产品良品率,满足设计和生产要求。展开更多
In this study,FLUENT software was employed to simulate the flow pattern and water depth changes in a 120° sharp bend at four discharge rates.To verify the numerical model,a 90° sharp bend was first modeled w...In this study,FLUENT software was employed to simulate the flow pattern and water depth changes in a 120° sharp bend at four discharge rates.To verify the numerical model,a 90° sharp bend was first modeled with a three-dimensional numerical model,and the results were compared with available experimental results.Based on the numerical model validation,a 120° bend was simulated.The results show that the rate of increase of the water depth at the cross-section located 40 cm before the bend,compared with the cross-sections located 40 cm and 80 cm after the bend,decreases with the increase of the normal water depth in the 120° curved channel.Moreover,with increasing normal water depth,the dimensionless water depth change decreases at all cross-sections.At the interior cross-sections of the bend,the transverse water depth slope of the inner half-width is always greater than that of the outer half-width of the channel.Hence,the water depth slope is nonlinear at each crosssection in sharp bends.Two equations reflecting the relationships between the maximum and minimum dimensionless water depths and the normal water depth throughout the channel were obtained.展开更多
基金the National Natural Science Foundation(52004285)Fundamental Research Funds for the Central Universities from China University of Mining and Technology-Beijing(JCCXXNY06)the Open Fund of State Key Laboratory Cultivation Base for Gas Geology and Gas Control(Henan Polytechnic University)(WS2021A03).
文摘Liquid nitrogen has shown excellent performances as a good fracturing medium in the extraction of unconventional natural gas,and its application in coalbed methane extraction is currently a research hotspot.This study focuses on the acoustic emission properties of coal specimens treated utilizing liquid nitrogen with varying initial temperatures in a three-point bending environment.Through examination of the load-displacement curves of the considered coal samples,their mechanical properties are also revealed for different initial temperatures and cycling frequencies.The findings demonstrate a gradual decline in the maximum load capacity of coal rock as the temperature rises.Similarly,when subjected to the same temperature,an escalation in the cycling frequency leads to a reduction in the peak load of coal rock.This suggests that both temperature and cycling frequency exert a notable impact on the fracturing efficacy of liquid nitrogen.Freeze-thaw cycling treatments and exposure to high-temperature conditions can activate preexisting damage in the coal rock,and,accordingly,influence its mechanical properties.In particular,throughout the progressive loading of coal rock samples,the failure mechanisms are predominantly characterized by the occurrence of tensile cracks,succeeded by the development,spread,and fracture of shear fissures.
文摘In this study,FLUENT software was employed to simulate the flow pattern and water depth changes in a 120° sharp bend at four discharge rates.To verify the numerical model,a 90° sharp bend was first modeled with a three-dimensional numerical model,and the results were compared with available experimental results.Based on the numerical model validation,a 120° bend was simulated.The results show that the rate of increase of the water depth at the cross-section located 40 cm before the bend,compared with the cross-sections located 40 cm and 80 cm after the bend,decreases with the increase of the normal water depth in the 120° curved channel.Moreover,with increasing normal water depth,the dimensionless water depth change decreases at all cross-sections.At the interior cross-sections of the bend,the transverse water depth slope of the inner half-width is always greater than that of the outer half-width of the channel.Hence,the water depth slope is nonlinear at each crosssection in sharp bends.Two equations reflecting the relationships between the maximum and minimum dimensionless water depths and the normal water depth throughout the channel were obtained.
