Under hypersonic flow conditions, the complicated gas-graphene interactions including surface catalysis and surface ablation would occur concurrently and intervene together with the thermodynamic response induced by s...Under hypersonic flow conditions, the complicated gas-graphene interactions including surface catalysis and surface ablation would occur concurrently and intervene together with the thermodynamic response induced by spacecraft reentry. In this work, the competing effects of surface heterogeneous catalytic recombination and ablation characteristics at elevated temperatures are investigated using the Reactive Molecular Dynamics(RMD) simulation method. A GasSurface Interaction(GSI) model is established to simulate the collisions of hyper-enthalpy atomic oxygen on graphene films in the temperature range of 500–2500 K. A critical temperature Tcaround900 K is identified to distinguish the graphene responses into two parts: at T < T_(c), the heterogeneous surface catalysis dominates, while the surface ablation plays a leading role at T > T_(c). Contradicting to the traditional Arrhenius expression that the recombination coefficient increases with the increase of surface temperature, the value is found to be relatively uniform at T < T_(c) but declines sharply as the surface temperature increases further due to the competing ablation effect. The occurrence of surface ablation decreases the amounts of active sites on the graphene surface for oxygen adsorption, leading to reduced recombination coefficient from both Langmuir-Hinshelwood(L-H) and Eley-Rideal(E-R) mechanisms. It suggests that the traditional Computational Fluid Dynamics(CFD) simulation method, which relies on the Arrhenius-type catalysis model, would result in large discrepancies in predicting aerodynamic heat for carbon-based materials during reentry into strong aerodynamic thermal environment.展开更多
The instantaneous degradation of erosion surface of ethylene propylene diene monomer(EPDM)insulation subjected to the particle-laden flow in two operating conditions was measured by using a real-time X-ray radiography...The instantaneous degradation of erosion surface of ethylene propylene diene monomer(EPDM)insulation subjected to the particle-laden flow in two operating conditions was measured by using a real-time X-ray radiography system.The images of its erosion state and dynamic ablation rate were obtained.And the charring-layer was analyzed by using SEM and energy spectrum.The experimental results indicate that the erosion rate of EPDM insulation layer impacted by low speed and low concentration particle flow is relatively small in the 1st second since the motor starting,but increases rapidly in 1 to 2.5 s,while the erosion rate of EPDM insulation layer impacted by high speed and high concentration particle flow increases rapidly in the 1st second;the ablation rate at the section eroded intensively by particle flow increases at first,then decreases,and goes to stabilization after 4.5 s;the higher speed and concentration particle flow are,the deeper particles get into charring layer,which lead to more thermal increment and thinner charring layer.展开更多
We investigate the angular distribution and average kinetic energy of ions produced during ultrafast laser ablation （ULA） of a copper target in high vacuum. Laser produced plasma （LPP） is induced by irradiating th...We investigate the angular distribution and average kinetic energy of ions produced during ultrafast laser ablation （ULA） of a copper target in high vacuum. Laser produced plasma （LPP） is induced by irradiating the target with Ti：Sapphire laser pulses of -50 fs and 800 nm at an angle of incidence of 45°. An ion probe is moved along a circular path around the ablation spot, thereby allowing characterization of the time-of-flight （TOF） of ions at different angles relative to the normal target. The angular distribution of the ion flux is well-described by an adiabatic and isentropic expansion model of a plume produced by solid-target laser ablation （LA）. The angular width of the ion flux becomes narrower with increasing laser fluence. Moreover, the ion average kinetic energy is forward-peaked and shows a stronger dependence on the laser pulse fluence than on the ion flux. Such results can be ascribed to space charge effects that occur during the early stages of LPP formation.展开更多
基金the Manned Space Engineering Technology (No. ZS2020103001)the National Natural Science Foundation of China (No. 52006004)+1 种基金National Numerical Wind Tunnel Project of China (No. NNW2018-ZT3A05)the Open Fund of Key Laboratory of Icing and Anti/De-icing (No. IADL20190102)
文摘Under hypersonic flow conditions, the complicated gas-graphene interactions including surface catalysis and surface ablation would occur concurrently and intervene together with the thermodynamic response induced by spacecraft reentry. In this work, the competing effects of surface heterogeneous catalytic recombination and ablation characteristics at elevated temperatures are investigated using the Reactive Molecular Dynamics(RMD) simulation method. A GasSurface Interaction(GSI) model is established to simulate the collisions of hyper-enthalpy atomic oxygen on graphene films in the temperature range of 500–2500 K. A critical temperature Tcaround900 K is identified to distinguish the graphene responses into two parts: at T < T_(c), the heterogeneous surface catalysis dominates, while the surface ablation plays a leading role at T > T_(c). Contradicting to the traditional Arrhenius expression that the recombination coefficient increases with the increase of surface temperature, the value is found to be relatively uniform at T < T_(c) but declines sharply as the surface temperature increases further due to the competing ablation effect. The occurrence of surface ablation decreases the amounts of active sites on the graphene surface for oxygen adsorption, leading to reduced recombination coefficient from both Langmuir-Hinshelwood(L-H) and Eley-Rideal(E-R) mechanisms. It suggests that the traditional Computational Fluid Dynamics(CFD) simulation method, which relies on the Arrhenius-type catalysis model, would result in large discrepancies in predicting aerodynamic heat for carbon-based materials during reentry into strong aerodynamic thermal environment.
基金Sponsored by the National Nature Science Foundation of China(50976095)
文摘The instantaneous degradation of erosion surface of ethylene propylene diene monomer(EPDM)insulation subjected to the particle-laden flow in two operating conditions was measured by using a real-time X-ray radiography system.The images of its erosion state and dynamic ablation rate were obtained.And the charring-layer was analyzed by using SEM and energy spectrum.The experimental results indicate that the erosion rate of EPDM insulation layer impacted by low speed and low concentration particle flow is relatively small in the 1st second since the motor starting,but increases rapidly in 1 to 2.5 s,while the erosion rate of EPDM insulation layer impacted by high speed and high concentration particle flow increases rapidly in the 1st second;the ablation rate at the section eroded intensively by particle flow increases at first,then decreases,and goes to stabilization after 4.5 s;the higher speed and concentration particle flow are,the deeper particles get into charring layer,which lead to more thermal increment and thinner charring layer.
基金supported by the China National Scholarship Fund,the Executive Programme Italy-China for the years 2010–2012(No.CN10M02)the National Natural Science Foundation of China(No.11104201)+1 种基金the Key Laboratory of Opto-electronic Information Technology,Ministry of Education(Tianjin University)Open Fundthe European Union Seventh Framework Programme(FP7/2007–2013)(No.264098-MAMA)
文摘We investigate the angular distribution and average kinetic energy of ions produced during ultrafast laser ablation （ULA） of a copper target in high vacuum. Laser produced plasma （LPP） is induced by irradiating the target with Ti：Sapphire laser pulses of -50 fs and 800 nm at an angle of incidence of 45°. An ion probe is moved along a circular path around the ablation spot, thereby allowing characterization of the time-of-flight （TOF） of ions at different angles relative to the normal target. The angular distribution of the ion flux is well-described by an adiabatic and isentropic expansion model of a plume produced by solid-target laser ablation （LA）. The angular width of the ion flux becomes narrower with increasing laser fluence. Moreover, the ion average kinetic energy is forward-peaked and shows a stronger dependence on the laser pulse fluence than on the ion flux. Such results can be ascribed to space charge effects that occur during the early stages of LPP formation.
