目的采用网状Meta分析的方法,评价各种气道湿化温化方法以预防非机械通气患者肺部感染的治疗效果。方法通过计算机结合手工检索了PubMed、Embase、Web of Science、Wanfang data和CNKI数据库,查找了关于国内气管切开术后非机械通气患者...目的采用网状Meta分析的方法,评价各种气道湿化温化方法以预防非机械通气患者肺部感染的治疗效果。方法通过计算机结合手工检索了PubMed、Embase、Web of Science、Wanfang data和CNKI数据库,查找了关于国内气管切开术后非机械通气患者的湿化方法的随机对照试验(RCT),由2名评价员独立筛选文献,提取资料,采用Stata14.0软件进行网状Meta分析。结果在3342篇文献中,最终有25篇纳入Meta分析,涉及6种气道湿化方法,有效性排序:人工鼻第1位、文丘里湿化装置第2位、持续雾化第3位、间断雾化第4位、持续滴入第5位、间断滴入湿化第6位。结论人工鼻装置和文丘里湿化装置的有效性逐渐被国内同行认可,Meta分析显示其对预防肺部感染有效性较好,值得推广。展开更多
Unsteady turbulent cavitation flows in a Venturi-type section and around a NACA0012 hydrofoil were simulated by two-dimensional computations of viscous compressible turbulent flow model. The Venturi-type section flow ...Unsteady turbulent cavitation flows in a Venturi-type section and around a NACA0012 hydrofoil were simulated by two-dimensional computations of viscous compressible turbulent flow model. The Venturi-type section flow proved numerical precision and reliability of the physical model and the code, and further the cavitation around NACA0012 foil was investigated. These flows were calculated with a code of SIMPLE-type finite volume scheme, associated with a barotropic vapor/liquid state law which strongly links density and pressure variation. To simulate turbulent flows, modified RNG k-ε model was used. Numerical results obtained in the Venturi-type flow simulated periodic shedding of sheet cavity and was compared with experiment data, and the results of the NACA0012 foil show quasi-periodic vortex cavitation phenomenon. Results obtained concerning cavity shape and unsteady behavior, void ratio, and velocity field were found in good agreement with experiment ones.展开更多
The venturi meter has an advantage in its use,because it can measure flow without being much affected by the type of the measured fluid or flow conditions.Hence,it has excellent versatility and is being widely applied...The venturi meter has an advantage in its use,because it can measure flow without being much affected by the type of the measured fluid or flow conditions.Hence,it has excellent versatility and is being widely applied in many industries.The flow of a liquid containing air is a representative example of a multiphase flow and exhibits complex flow characteristics.In particular,the greater the gas volume fraction（GVF）,the more inhomogeneous the flow becomes.As a result,using a venturi meter to measure the rate of a flow that has a high GVF generates an error.In this study,the cause of the error occurred in measuring the flow rate for the multiphase flow when using the venturi meter for analysis by CFD.To ensure the reliability of this study,the accuracy of the multiphase flow models for numerical analysis was verified through comparison between the calculated results of numerical analysis and the experimental data.As a result,the Grace model,which is a multiphase flow model established by an experiment with water and air,was confirmed to have the highest reliability.Finally,the characteristics of the internal flow Held about the multiphase flow analysis result generated by applying the Grace model were analyzed to find the cause of the uncertainty occurring when measuring the flow rate of the multiphase flow using the venturi meter.A phase separation phenomenon occurred due to a density difference of water and air inside the venturi,and flow inhomogeneity happened according to the flow velocity difference of each phase.It was confirmed that this flow inhomogeneity increased as the GVF increased due to the uncertainty of the flow measurement.展开更多
The performance of a Venturi tube used in wet gas flow have been explored mainly under higher-pressure condition, but very often, low-pressure test exists in some oil and gas fields in Tianjin Dagang Oil and Gas Field...The performance of a Venturi tube used in wet gas flow have been explored mainly under higher-pressure condition, but very often, low-pressure test exists in some oil and gas fields in Tianjin Dagang Oil and Gas Field in China. In this study, the performance of horizontally mounted Venturi meters in low-pressure wet gas flow is discussed. Three 50 mm Venturi meters were tested systematically, with fl values of 0.4048, 0.55 and 0.70, the opera- tion pressure of 0.15 MPa, 0.20 MPa, 0.25 MPa, the gas densiometric Froude number from 0.6 to 2.0, the modified Lockhart-Maretinelli parameter from 0.0022 to 0.06, and the ratio of the gas liquid mass flow rate from 0.5 to 0.99. The effects of modified Lockhart-Maretinelli parameter, pressure, gas densiometric Froude number, diameter ratio, and gas-liquid mass flow rate ratio to the Venturi tube are analyzed with new independent data. Furthermore, low-pressure performance was compared with that under high pressure.展开更多
针对柴油机在低速、大负荷工况下引入EGR(exhaust gas recirculation)气体困难的实际情况,该文采用在中冷器后安装一个文丘里管的方法提高对EGR的引射能力。通过计算初步确定了文丘里管的喉口直径,并设计了3种不同结构尺寸的文丘里管,...针对柴油机在低速、大负荷工况下引入EGR(exhaust gas recirculation)气体困难的实际情况,该文采用在中冷器后安装一个文丘里管的方法提高对EGR的引射能力。通过计算初步确定了文丘里管的喉口直径,并设计了3种不同结构尺寸的文丘里管,进行了相关试验。试验结果表明,随着发动机转速的提高,气体流量增加,文丘里管的降压作用增强;EGR阀前与文丘里管喉口的压差随着发动机转速先减小后增加,在1100到1600r/min转速范围内,该压差为负值,不利于引入EGR气体;在2200r/min时,随着发动机负荷的增加,EGR阀前压力始终大于文丘里管前压力,即使没有文丘里管,发动机也可以顺利引入EGR,但二者压差随着负荷的增加而减小,导致高负荷时EGR率降低;文丘里管的降压作用随发动机负荷的增加而增加,EGR引射能力随负荷的变化不明显;在试验负荷范围内,文丘里管前后的压力损失始终大于5kPa;在2200r/min时,3种喉口直径的文丘里管的EGR引射能力随着负荷的增加均有增强的趋势,但直径较小的文丘里管EGR阀前与喉口压差较大,容易实现较高的EGR率;但在1600r/min时,3种文丘里管的EGR引射能力均随着负荷的增加而减小;当扭矩超过470N·m时,随着文丘里管喉口直径的增加,EGR阀前与文丘里管喉口压差逐渐降低,引入EGR气体的难度逐渐增加。研究结果可为增压中冷柴油机废气再循环系统文丘里管的设计和应用提供参考。展开更多
文摘目的采用网状Meta分析的方法,评价各种气道湿化温化方法以预防非机械通气患者肺部感染的治疗效果。方法通过计算机结合手工检索了PubMed、Embase、Web of Science、Wanfang data和CNKI数据库,查找了关于国内气管切开术后非机械通气患者的湿化方法的随机对照试验(RCT),由2名评价员独立筛选文献,提取资料,采用Stata14.0软件进行网状Meta分析。结果在3342篇文献中,最终有25篇纳入Meta分析,涉及6种气道湿化方法,有效性排序:人工鼻第1位、文丘里湿化装置第2位、持续雾化第3位、间断雾化第4位、持续滴入第5位、间断滴入湿化第6位。结论人工鼻装置和文丘里湿化装置的有效性逐渐被国内同行认可,Meta分析显示其对预防肺部感染有效性较好,值得推广。
基金Project supported by the National Natural Science Foundation of China (Grant No: 10372061) the Doctor Foundation (Grant No: 20030248001).
文摘Unsteady turbulent cavitation flows in a Venturi-type section and around a NACA0012 hydrofoil were simulated by two-dimensional computations of viscous compressible turbulent flow model. The Venturi-type section flow proved numerical precision and reliability of the physical model and the code, and further the cavitation around NACA0012 foil was investigated. These flows were calculated with a code of SIMPLE-type finite volume scheme, associated with a barotropic vapor/liquid state law which strongly links density and pressure variation. To simulate turbulent flows, modified RNG k-ε model was used. Numerical results obtained in the Venturi-type flow simulated periodic shedding of sheet cavity and was compared with experiment data, and the results of the NACA0012 foil show quasi-periodic vortex cavitation phenomenon. Results obtained concerning cavity shape and unsteady behavior, void ratio, and velocity field were found in good agreement with experiment ones.
基金supported by the Industrial Infrastructure Program through The Korea Institute for Advancement of Technology(KIAT) Grant funded by the Korea government Ministry of Trade,Industry and Energy(Grant N0000502)
文摘The venturi meter has an advantage in its use,because it can measure flow without being much affected by the type of the measured fluid or flow conditions.Hence,it has excellent versatility and is being widely applied in many industries.The flow of a liquid containing air is a representative example of a multiphase flow and exhibits complex flow characteristics.In particular,the greater the gas volume fraction（GVF）,the more inhomogeneous the flow becomes.As a result,using a venturi meter to measure the rate of a flow that has a high GVF generates an error.In this study,the cause of the error occurred in measuring the flow rate for the multiphase flow when using the venturi meter for analysis by CFD.To ensure the reliability of this study,the accuracy of the multiphase flow models for numerical analysis was verified through comparison between the calculated results of numerical analysis and the experimental data.As a result,the Grace model,which is a multiphase flow model established by an experiment with water and air,was confirmed to have the highest reliability.Finally,the characteristics of the internal flow Held about the multiphase flow analysis result generated by applying the Grace model were analyzed to find the cause of the uncertainty occurring when measuring the flow rate of the multiphase flow using the venturi meter.A phase separation phenomenon occurred due to a density difference of water and air inside the venturi,and flow inhomogeneity happened according to the flow velocity difference of each phase.It was confirmed that this flow inhomogeneity increased as the GVF increased due to the uncertainty of the flow measurement.
基金the National High Technology Research and Development Program of China(2006AA04Z167,2007AA04Z180)
文摘The performance of a Venturi tube used in wet gas flow have been explored mainly under higher-pressure condition, but very often, low-pressure test exists in some oil and gas fields in Tianjin Dagang Oil and Gas Field in China. In this study, the performance of horizontally mounted Venturi meters in low-pressure wet gas flow is discussed. Three 50 mm Venturi meters were tested systematically, with fl values of 0.4048, 0.55 and 0.70, the opera- tion pressure of 0.15 MPa, 0.20 MPa, 0.25 MPa, the gas densiometric Froude number from 0.6 to 2.0, the modified Lockhart-Maretinelli parameter from 0.0022 to 0.06, and the ratio of the gas liquid mass flow rate from 0.5 to 0.99. The effects of modified Lockhart-Maretinelli parameter, pressure, gas densiometric Froude number, diameter ratio, and gas-liquid mass flow rate ratio to the Venturi tube are analyzed with new independent data. Furthermore, low-pressure performance was compared with that under high pressure.
文摘针对柴油机在低速、大负荷工况下引入EGR(exhaust gas recirculation)气体困难的实际情况,该文采用在中冷器后安装一个文丘里管的方法提高对EGR的引射能力。通过计算初步确定了文丘里管的喉口直径,并设计了3种不同结构尺寸的文丘里管,进行了相关试验。试验结果表明,随着发动机转速的提高,气体流量增加,文丘里管的降压作用增强;EGR阀前与文丘里管喉口的压差随着发动机转速先减小后增加,在1100到1600r/min转速范围内,该压差为负值,不利于引入EGR气体;在2200r/min时,随着发动机负荷的增加,EGR阀前压力始终大于文丘里管前压力,即使没有文丘里管,发动机也可以顺利引入EGR,但二者压差随着负荷的增加而减小,导致高负荷时EGR率降低;文丘里管的降压作用随发动机负荷的增加而增加,EGR引射能力随负荷的变化不明显;在试验负荷范围内,文丘里管前后的压力损失始终大于5kPa;在2200r/min时,3种喉口直径的文丘里管的EGR引射能力随着负荷的增加均有增强的趋势,但直径较小的文丘里管EGR阀前与喉口压差较大,容易实现较高的EGR率;但在1600r/min时,3种文丘里管的EGR引射能力均随着负荷的增加而减小;当扭矩超过470N·m时,随着文丘里管喉口直径的增加,EGR阀前与文丘里管喉口压差逐渐降低,引入EGR气体的难度逐渐增加。研究结果可为增压中冷柴油机废气再循环系统文丘里管的设计和应用提供参考。
