Diffusion of a solute in turbulent flows through a circular pipe or tunnel is an important aspect of environmental safety. In this study, the diffusion coefficient of turbulent flow in circular pipe has been simulated...Diffusion of a solute in turbulent flows through a circular pipe or tunnel is an important aspect of environmental safety. In this study, the diffusion coefficient of turbulent flow in circular pipe has been simulated by the Discrete Tracer Point Method (DTPM). The DTPM is a Lagrangian numerical method by a number of imaginary point displacement which satisfy turbulent mixing by velocity fluctuations, Reynolds stress, average velocity profile and a turbulent stochastic model. Numerical simulation results of points’ distribution by DTPM have been compared with the analytical solution for turbulent plug-flow. For the case of turbulent circular pipe flow, the appropriate DTPM calculation time step has been investigated using a constantβ, which represents the ratio between average mixing lengths over diameter of circular pipe. The evaluated values of diffusion coefficient by DTPM have been found to be in good agreement with Taylor’s analytical equation for turbulent circular pipe flow by givingβ=0.04 to 0.045. Further, history matching of experimental tracer gas measurement through turbulent smooth-straight pipe flow has been presented and the results showed good agreement.展开更多
为研究气流对扩散层输水性的影响,构建二维模型表征扩散层纤维结构特征;联合VOF(Volume of Fluid)方法、N-S方程、Darcy定律及毛细压力方程,建立多孔介质内气液控制方程,跟踪气液流动界面,分析气流压力、温度和输入模式与不同孔隙率扩...为研究气流对扩散层输水性的影响,构建二维模型表征扩散层纤维结构特征;联合VOF(Volume of Fluid)方法、N-S方程、Darcy定律及毛细压力方程,建立多孔介质内气液控制方程,跟踪气液流动界面,分析气流压力、温度和输入模式与不同孔隙率扩散层水输运状态的关系,阐明气流与孔隙结构耦合作用对扩散层水分布的影响机理。结果表明:扩散层内气流分布直接影响水的输运,而气流状态与扩散层孔隙结构特征密切相关;增大气体输入间隔对于增进扩散层排水效果显著。该研究对于提升扩散层的输水性具有借鉴意义。展开更多
目的比较气流冲击结合间断声门吸引法、持续声门下吸引结合灌洗法在降低机械通气并发症上的效果。方法选择行气管切开、机械通气>48 h的病人40例,按住院时间先后分为气流冲击组和灌洗组。气流冲击组采用间断声门下吸引结合每日2次气...目的比较气流冲击结合间断声门吸引法、持续声门下吸引结合灌洗法在降低机械通气并发症上的效果。方法选择行气管切开、机械通气>48 h的病人40例,按住院时间先后分为气流冲击组和灌洗组。气流冲击组采用间断声门下吸引结合每日2次气流冲击的方法清除气囊上滞留物,灌洗组采用持续声门下吸引结合每日2次声门下灌洗的方法,两组每日记录气囊上吸引量、呛咳、气道黏膜受损出血情况,并在人工气道建立1、3、7 d留取下呼吸道分泌物和声门下滞留物,进行细菌培养,比较两组病人1周气囊上吸引量、呛咳、气道黏膜受损出血及呼吸机相关性肺炎(VAP)的发生情况。结果灌洗组与气流组病人比较中3 d VAP发生率分别为15%、5%(P>0.05)、7 d VAP发生率分别为30%、15%(P>0.05),气囊上吸引量分别为(85.30±33.50)、(84.80±35.58)m L·d^(-1)(P>0.05),呛咳发生次数分别为(6.36±1.33)、(4.60±1.83)次(P<0.01)、气道黏膜受损出血的发生率分别为35%、5%(P<0.05)。结论气管切开病人使用气流冲击结合间断声门下吸引法较持续声门下吸引结合灌洗法,可以降低病人呛咳、气道黏膜受损出血等并发症的发生,减轻病人痛苦。展开更多
文摘Diffusion of a solute in turbulent flows through a circular pipe or tunnel is an important aspect of environmental safety. In this study, the diffusion coefficient of turbulent flow in circular pipe has been simulated by the Discrete Tracer Point Method (DTPM). The DTPM is a Lagrangian numerical method by a number of imaginary point displacement which satisfy turbulent mixing by velocity fluctuations, Reynolds stress, average velocity profile and a turbulent stochastic model. Numerical simulation results of points’ distribution by DTPM have been compared with the analytical solution for turbulent plug-flow. For the case of turbulent circular pipe flow, the appropriate DTPM calculation time step has been investigated using a constantβ, which represents the ratio between average mixing lengths over diameter of circular pipe. The evaluated values of diffusion coefficient by DTPM have been found to be in good agreement with Taylor’s analytical equation for turbulent circular pipe flow by givingβ=0.04 to 0.045. Further, history matching of experimental tracer gas measurement through turbulent smooth-straight pipe flow has been presented and the results showed good agreement.
文摘为研究气流对扩散层输水性的影响,构建二维模型表征扩散层纤维结构特征;联合VOF(Volume of Fluid)方法、N-S方程、Darcy定律及毛细压力方程,建立多孔介质内气液控制方程,跟踪气液流动界面,分析气流压力、温度和输入模式与不同孔隙率扩散层水输运状态的关系,阐明气流与孔隙结构耦合作用对扩散层水分布的影响机理。结果表明:扩散层内气流分布直接影响水的输运,而气流状态与扩散层孔隙结构特征密切相关;增大气体输入间隔对于增进扩散层排水效果显著。该研究对于提升扩散层的输水性具有借鉴意义。
文摘目的比较气流冲击结合间断声门吸引法、持续声门下吸引结合灌洗法在降低机械通气并发症上的效果。方法选择行气管切开、机械通气>48 h的病人40例,按住院时间先后分为气流冲击组和灌洗组。气流冲击组采用间断声门下吸引结合每日2次气流冲击的方法清除气囊上滞留物,灌洗组采用持续声门下吸引结合每日2次声门下灌洗的方法,两组每日记录气囊上吸引量、呛咳、气道黏膜受损出血情况,并在人工气道建立1、3、7 d留取下呼吸道分泌物和声门下滞留物,进行细菌培养,比较两组病人1周气囊上吸引量、呛咳、气道黏膜受损出血及呼吸机相关性肺炎(VAP)的发生情况。结果灌洗组与气流组病人比较中3 d VAP发生率分别为15%、5%(P>0.05)、7 d VAP发生率分别为30%、15%(P>0.05),气囊上吸引量分别为(85.30±33.50)、(84.80±35.58)m L·d^(-1)(P>0.05),呛咳发生次数分别为(6.36±1.33)、(4.60±1.83)次(P<0.01)、气道黏膜受损出血的发生率分别为35%、5%(P<0.05)。结论气管切开病人使用气流冲击结合间断声门下吸引法较持续声门下吸引结合灌洗法,可以降低病人呛咳、气道黏膜受损出血等并发症的发生,减轻病人痛苦。
