The objective of this study is to investigate critical velocity and smoke maximum temperature beneath the ceiling in the connected area of branch tunnel with varying fire locations.The fire sources were located in the...The objective of this study is to investigate critical velocity and smoke maximum temperature beneath the ceiling in the connected area of branch tunnel with varying fire locations.The fire sources were located in the divergent connected area of the branch tunnel,to imitate traffic accidents near the branch point.A 1/20 scale model branch tunnel was built including main line before branch,main line after branch,and ramp.Experimental tests and numerical simulations were performed to explore smoke movement characteristics with longitudinal ventilation.The results showed that the enlarged cross-sectional area in branch tunnel caused the shortening of the back-layering length,and a modified model of back-layering length was proposed.The higher tunnel height in this work affected the critical condition of large fire;it caused a larger transition point of dimensionless critical velocity.A revised model was proposed for the maximum temperature rise of tunnel fires in the connected area of branch tunnel.The critical velocity kept unchanged when the branch angle increased from 0°to 20°because there is little change in the longitudinal smoke temperature.As the local tunnel width of fire source was increased,the required critical velocity was increased while the local effective velocity kept nearly the same.展开更多
针对地铁隧道内列车车厢所组构的双狭长受限空间,开展隧道内纵向通风对列车车厢火灾烟气温度特性影响的研究。考虑隧道内通风风速平行于列车车厢侧向开口的独特特征,研究不同纵向通风风速和热释放速率下隧道内列车车厢火灾的烟气最高温...针对地铁隧道内列车车厢所组构的双狭长受限空间,开展隧道内纵向通风对列车车厢火灾烟气温度特性影响的研究。考虑隧道内通风风速平行于列车车厢侧向开口的独特特征,研究不同纵向通风风速和热释放速率下隧道内列车车厢火灾的烟气最高温升和近火源区纵向温度分布。结果表明:由于双重受限边界的限制,先前经典的单狭长受限空间所得最高烟气温升预测模型(LI Y Z等)过低地预测了车厢顶棚下方烟气温度,特别是v’>0.19的工况;此外,由于隧道内强制风流通过车厢侧向开口对车厢火灾的独特作用机制,本文所研究工况中隧道内纵向气流对车厢烟气温度特性的影响并不显著。通过对比他人试验验证和分析,提出了列车车厢顶棚下方最高烟气温升及近火源区的经验预测模型。展开更多
One of the biggest puzzles concerning the cuprate high temperature superconductors is what determines the maximum transition temperature(Tc,max), which varies from less than 30 to above 130 K in different compounds.De...One of the biggest puzzles concerning the cuprate high temperature superconductors is what determines the maximum transition temperature(Tc,max), which varies from less than 30 to above 130 K in different compounds.Despite this dramatic variation, a robust trend is that within each family, the double-layer compound always has higher Tc,maxthan the single-layer counterpart. Here we use scanning tunneling microscopy to investigate the electronic structure of four cuprate parent compounds belonging to two different families. We find that within each family, the double layer compound has a much smaller charge transfer gap size(DCT), indicating a clear anticorrelation between DCTand Tc,max. These results suggest that the charge transfer gap plays a key role in the superconducting physics of cuprates, which shed important new light on the high Tc mechanism from doped Mott insulator perspective.展开更多
Ceiling gas temperature rise is an important evaluation indicator determining the level of risk in a subway tunnel fire.However,very little literature has been found that has addressed the emergency when a fired subwa...Ceiling gas temperature rise is an important evaluation indicator determining the level of risk in a subway tunnel fire.However,very little literature has been found that has addressed the emergency when a fired subway train with lateral multiple openings stops in the interval tunnel.Hence,a battery of full-scale numerical simulations were employed to address the impact of train fire location on the gas temperature beneath the train ceiling.Numerical results showed that the ceiling gas temperature rise is affected by the pressure difference on both sides of fire source and the backflow from the end wall,which depends on the heat release rate and the fire location.The ceiling gas temperature rise decays exponentially in the process of longitudinal spread,and it can be predicted by a dimensionless model with a sum of two exponential equations.Finally,based on a critical fire location(L'cr=0.667),two exponential equations were developed to quantitatively express the influences of the fire size and the fire location on the maximum ceiling gas temperature.The research results can be utilized for providing an initial understanding of the smoke propagation in a subway train fire.展开更多
基金This research was supported by the National Nature Science Foundation of China(No.52076066)Key Research and Development Project of Zhejiang Province(No.2018C03029)+1 种基金Zhejiang Provincial Natural Science Foundation of China(No.LQ19E040005)Fellowship of China Postdoctoral Science Foundation(No.2021M693042).
文摘The objective of this study is to investigate critical velocity and smoke maximum temperature beneath the ceiling in the connected area of branch tunnel with varying fire locations.The fire sources were located in the divergent connected area of the branch tunnel,to imitate traffic accidents near the branch point.A 1/20 scale model branch tunnel was built including main line before branch,main line after branch,and ramp.Experimental tests and numerical simulations were performed to explore smoke movement characteristics with longitudinal ventilation.The results showed that the enlarged cross-sectional area in branch tunnel caused the shortening of the back-layering length,and a modified model of back-layering length was proposed.The higher tunnel height in this work affected the critical condition of large fire;it caused a larger transition point of dimensionless critical velocity.A revised model was proposed for the maximum temperature rise of tunnel fires in the connected area of branch tunnel.The critical velocity kept unchanged when the branch angle increased from 0°to 20°because there is little change in the longitudinal smoke temperature.As the local tunnel width of fire source was increased,the required critical velocity was increased while the local effective velocity kept nearly the same.
文摘针对地铁隧道内列车车厢所组构的双狭长受限空间,开展隧道内纵向通风对列车车厢火灾烟气温度特性影响的研究。考虑隧道内通风风速平行于列车车厢侧向开口的独特特征,研究不同纵向通风风速和热释放速率下隧道内列车车厢火灾的烟气最高温升和近火源区纵向温度分布。结果表明:由于双重受限边界的限制,先前经典的单狭长受限空间所得最高烟气温升预测模型(LI Y Z等)过低地预测了车厢顶棚下方烟气温度,特别是v’>0.19的工况;此外,由于隧道内强制风流通过车厢侧向开口对车厢火灾的独特作用机制,本文所研究工况中隧道内纵向气流对车厢烟气温度特性的影响并不显著。通过对比他人试验验证和分析,提出了列车车厢顶棚下方最高烟气温升及近火源区的经验预测模型。
基金supported by the National Natural Science Foundation of China and Ministry of Science and Technology of the People’s Republic of Chinafinancial support from the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (XDB07020300)
文摘One of the biggest puzzles concerning the cuprate high temperature superconductors is what determines the maximum transition temperature(Tc,max), which varies from less than 30 to above 130 K in different compounds.Despite this dramatic variation, a robust trend is that within each family, the double-layer compound always has higher Tc,maxthan the single-layer counterpart. Here we use scanning tunneling microscopy to investigate the electronic structure of four cuprate parent compounds belonging to two different families. We find that within each family, the double layer compound has a much smaller charge transfer gap size(DCT), indicating a clear anticorrelation between DCTand Tc,max. These results suggest that the charge transfer gap plays a key role in the superconducting physics of cuprates, which shed important new light on the high Tc mechanism from doped Mott insulator perspective.
基金This work was supported by the National Key Research and Development Program of China(No.2018YFC0807600)the National Natural Science Foundation of China(No.51776192),the Youth Innovation Promotion Association CAS(No.CX2320007001)the Fundamental Research Funds for the Central Universities(No.WK2320000048).
文摘Ceiling gas temperature rise is an important evaluation indicator determining the level of risk in a subway tunnel fire.However,very little literature has been found that has addressed the emergency when a fired subway train with lateral multiple openings stops in the interval tunnel.Hence,a battery of full-scale numerical simulations were employed to address the impact of train fire location on the gas temperature beneath the train ceiling.Numerical results showed that the ceiling gas temperature rise is affected by the pressure difference on both sides of fire source and the backflow from the end wall,which depends on the heat release rate and the fire location.The ceiling gas temperature rise decays exponentially in the process of longitudinal spread,and it can be predicted by a dimensionless model with a sum of two exponential equations.Finally,based on a critical fire location(L'cr=0.667),two exponential equations were developed to quantitatively express the influences of the fire size and the fire location on the maximum ceiling gas temperature.The research results can be utilized for providing an initial understanding of the smoke propagation in a subway train fire.
