Hydrogen energy has been widely used in various industrial processes.However,hydrogen explosion can cause significant loss of personnel and property,and explosion venting is an effective method to reduce the explosion...Hydrogen energy has been widely used in various industrial processes.However,hydrogen explosion can cause significant loss of personnel and property,and explosion venting is an effective method to reduce the explosion damage.The mechanism of hydrogen explosion venting has become an important research topic in hydrogen energy safety engineering.This study employs numerical simulation to explore the impact of vent parameters on the hydrogen-air explosion dynamics.A geometric model considering internal and external explosion is established.Results show that venting efficiency improves as the vent is positioned closer to the ignition or the number of vents increases.The peak internal overpressure increases by 1.2 times as the single vent moves from the ignition to near the end.The external explosion overpressure and dynamic pressure grows with the decrease of internal explosion venting efficiency.The flame front deflects toward the vent and ejects from the duct under the suction effect of the vent.The vortex flow characteristics near the vent cause the flame to deform as it propagates downstream.Vents located closer to the ignition induce the formation of a reverse flow field and lead to reverse propagation of the flame.The formation of symmetrical vortex regions within the flame causes it to compress,resulting in a longer external flame length as the vent is located farther from the ignition.The maximum flame speed increases by 1.1 times as the single vent moves from the ignition to near the end.Multiple flame propagation speed are exhibited under multiple vents conditions.展开更多
Objective To investigate the effects of extrinsic positive end-expiratory pressure (PEEPe) on work of breathing in patients with chronic obstructive pulmonary disease (COPD) and their corresponding mechanism.Methods...Objective To investigate the effects of extrinsic positive end-expiratory pressure (PEEPe) on work of breathing in patients with chronic obstructive pulmonary disease (COPD) and their corresponding mechanism.Methods Ten ventilated patients with COPD were included in the study. A Bicore CP-100 pulmonary monitor (Bicore Monitoring System, USA) was used for monitoring respiratory mechanics. First, dynamic intrinsic positive end-expiratory pressure (PEEPi,dyn) was measured when PEEPe was zero, which was called PEEPi,dynz. Then the PEEPe was set randomly at 0%, 40%, 60%, 80% and 100% of PEEPi,dynz respectively. Pulmonary mechanics and other parameters (heart rate, blood pressure and blood gas analysis) were measured 30 minutes after the level of PEEPe was changed.Results Work of breathing patient (WOBp), pressure time product, difference of esophageal pressure and PEEPi,dyn decreased significantly when PEEPe was applied, and continued decreasing as PEEPe was increased. Work of breathing ventilator increased significantly when PEEPe was increased to 80% and 100% of PEEPi,dynz. Significantly positive linear correlation was found between the changes in WOBp and in PEEPi,dyn.Conclusions WOBp decreases gradually as PEEPe is increased. WOBp decreases by narrowing the difference between the alveolus pressure and the central airway pressure at the end of expiration when PEEPe is applied.展开更多
基金funded by the National Key R&D Program of China,grant number no.2023YFB4301701.
文摘Hydrogen energy has been widely used in various industrial processes.However,hydrogen explosion can cause significant loss of personnel and property,and explosion venting is an effective method to reduce the explosion damage.The mechanism of hydrogen explosion venting has become an important research topic in hydrogen energy safety engineering.This study employs numerical simulation to explore the impact of vent parameters on the hydrogen-air explosion dynamics.A geometric model considering internal and external explosion is established.Results show that venting efficiency improves as the vent is positioned closer to the ignition or the number of vents increases.The peak internal overpressure increases by 1.2 times as the single vent moves from the ignition to near the end.The external explosion overpressure and dynamic pressure grows with the decrease of internal explosion venting efficiency.The flame front deflects toward the vent and ejects from the duct under the suction effect of the vent.The vortex flow characteristics near the vent cause the flame to deform as it propagates downstream.Vents located closer to the ignition induce the formation of a reverse flow field and lead to reverse propagation of the flame.The formation of symmetrical vortex regions within the flame causes it to compress,resulting in a longer external flame length as the vent is located farther from the ignition.The maximum flame speed increases by 1.1 times as the single vent moves from the ignition to near the end.Multiple flame propagation speed are exhibited under multiple vents conditions.
文摘Objective To investigate the effects of extrinsic positive end-expiratory pressure (PEEPe) on work of breathing in patients with chronic obstructive pulmonary disease (COPD) and their corresponding mechanism.Methods Ten ventilated patients with COPD were included in the study. A Bicore CP-100 pulmonary monitor (Bicore Monitoring System, USA) was used for monitoring respiratory mechanics. First, dynamic intrinsic positive end-expiratory pressure (PEEPi,dyn) was measured when PEEPe was zero, which was called PEEPi,dynz. Then the PEEPe was set randomly at 0%, 40%, 60%, 80% and 100% of PEEPi,dynz respectively. Pulmonary mechanics and other parameters (heart rate, blood pressure and blood gas analysis) were measured 30 minutes after the level of PEEPe was changed.Results Work of breathing patient (WOBp), pressure time product, difference of esophageal pressure and PEEPi,dyn decreased significantly when PEEPe was applied, and continued decreasing as PEEPe was increased. Work of breathing ventilator increased significantly when PEEPe was increased to 80% and 100% of PEEPi,dynz. Significantly positive linear correlation was found between the changes in WOBp and in PEEPi,dyn.Conclusions WOBp decreases gradually as PEEPe is increased. WOBp decreases by narrowing the difference between the alveolus pressure and the central airway pressure at the end of expiration when PEEPe is applied.
