Flow visualization and hot-wire measurement techniques were combined to investigate the influence of the size and number of tabs on jet flow field and vortex structure generation mechanism. Streamwise vortices generat...Flow visualization and hot-wire measurement techniques were combined to investigate the influence of the size and number of tabs on jet flow field and vortex structure generation mechanism. Streamwise vortices generated by the tabs of different sizes and numbers were observed from the flow visualization images. Combined with flow visualization, hot-wire measurement gave a quantitative insight of the effect of various tabbed jet flows. Instantaneous two-component velocity signals (longitudinal and transverse velocity components) at different cross sections along radius direction and streamwise direction with different tabbed jet nozzles were measured using hot-wire anemometer. Average flow field parameters of tabbed jet flow such as mean velocity, tur-bulence intensity, vorticity were analyzed and the effects of tabs with different sizes and numbers were compared with that of circular no-tab jet flow. It is revealed that the generation of a series of counter-rotating quasi-streamwise vortices, azimuthal vortices and double-row azi-muthal vortex are the reasons for mixing enhancement of tabbed turbulent jet flow.展开更多
In the radiant section of cracking furnace,the thermal cracking process is highly coupled with turbulent flow,heat transfer and mass transfer.In this paper,a three-dimensional simulation of propane pyrolysis reactor t...In the radiant section of cracking furnace,the thermal cracking process is highly coupled with turbulent flow,heat transfer and mass transfer.In this paper,a three-dimensional simulation of propane pyrolysis reactor tube is performed based on a detailed kinetic radical cracking scheme,combined with a comprehensive rigorous computational fluid dynamics(CFD)model.The eddy-dissipation-concept(EDC)model is introduced to deal with turbulence-chemistry interaction of cracking gas,especially for the multi-step radical kinetics.Considering the high aspect ratio and severe gradient phenomenon,numerical strategies such as grid resolution and refinement,stepping method and relaxation technique at different levels are employed to accelerate convergence.Large scale of radial nonuniformity in the vicinity of the tube wall is investigated.Spatial distributions of each radical reaction rate are first studied,and made it possible to identify the dominant elementary reactions.Additionally,a series of operating conditions including the feedstock feed rate,wall temperature profile and heat flux profile towards the reactor tubes are investigated.The obtained results can be used as scientific guide for further technical retrofit and operation optimization aiming at high conversion and selectivity of pyrolysis process.展开更多
The photodissociation of Br2 was investigated within the near-visible UV absorption band. Based on the potential curves for the ground and low-lying excited states, the optical cross-sections for the discrete transiti...The photodissociation of Br2 was investigated within the near-visible UV absorption band. Based on the potential curves for the ground and low-lying excited states, the optical cross-sections for the discrete transitions of C1^Пu,B^3Пou^+, A^3П1u←X^1∑g+ and their total energy absorption spectrum are derived, and the quantum yield of (Br+Br6*) channel are determined correspondingly. The one-dimensional Landau-Zener model is used to evaluate the behavior of curve crossing during photodissociation. The results indicate that the influence of nonadiabatic mechanism, which may be caused by the electronic-vibrational interplay between the 13 and C states, is negligibly small for the (Br+Br^*) channel. From the Landau-Zener modeling of the observed product recoil parameter β(Br+Br), the best-fit value of the coupling matrix elenment or coupling strength between the diabatic B and C state potentials is obtained.展开更多
In the present work we elucidate the thermodynamic mechanisms of femtosecond(fs)laser ablation of amorphous polystyrene by means of molecular dynamics(MD)simulations.The effects of extrinsic parameter of laser pulse i...In the present work we elucidate the thermodynamic mechanisms of femtosecond(fs)laser ablation of amorphous polystyrene by means of molecular dynamics(MD)simulations.The effects of extrinsic parameter of laser pulse intensity and intrinsic parameter of molecular architecture on the laser ablation are further studied.Simulation results show that the laser ablation-induced polymeric material removal is achieved by evaporation from the surface and expansion within the bulk.Furthermore,inter-chain sliding and intra-chain change also play important roles in the microscopic deformation of the material.It is found that both the laser pulse intensity and the arrangement of phenyl groups have significant influence on the fs laser ablation of polystyrene.展开更多
Sulfur dioxide (SO2) and nitrogen oxide (NOx) in flue gas can be removed by combining microwave induced catalysis and adsorption on activated carbon. The reaction mechanisms of desulfurization and denitrification ...Sulfur dioxide (SO2) and nitrogen oxide (NOx) in flue gas can be removed by combining microwave induced catalysis and adsorption on activated carbon. The reaction mechanisms of desulfurization and denitrification by microwave irradiation were analyzed based on the measurement of reaction products. Thermodynamic parameters for desulfurization and denitrification by thermal-carbon reduction were predicted according to the principles of thermodynamics. The experimental results indicated that the desulfurization and denitrification reaction processes include three reaction stages: slow reaction zone, transitional zone and rapid reaction zone. In high temperature zone, activation energies for the reduction of SO2 and nitrogen monoxide (NO) are 30.69 and 24.06 kJ mo1-1, respectively. This study shows that microwave can effectively enhance the removal of pollutants through its heating effect and the induced catalysis.展开更多
基金National Natural Science Foundation of China (No.10472081)Program for New Century Excellent Talents in Universities of Minis-try of Education of China and Plan of Tianjin Science and Technology Development (No.06TXTJJC13800)
文摘Flow visualization and hot-wire measurement techniques were combined to investigate the influence of the size and number of tabs on jet flow field and vortex structure generation mechanism. Streamwise vortices generated by the tabs of different sizes and numbers were observed from the flow visualization images. Combined with flow visualization, hot-wire measurement gave a quantitative insight of the effect of various tabbed jet flows. Instantaneous two-component velocity signals (longitudinal and transverse velocity components) at different cross sections along radius direction and streamwise direction with different tabbed jet nozzles were measured using hot-wire anemometer. Average flow field parameters of tabbed jet flow such as mean velocity, tur-bulence intensity, vorticity were analyzed and the effects of tabs with different sizes and numbers were compared with that of circular no-tab jet flow. It is revealed that the generation of a series of counter-rotating quasi-streamwise vortices, azimuthal vortices and double-row azi-muthal vortex are the reasons for mixing enhancement of tabbed turbulent jet flow.
基金Supported by the National Science&Technology Supporting Plan(2012BAF05B00)the National Basic Research Program(2012CB720500)
文摘In the radiant section of cracking furnace,the thermal cracking process is highly coupled with turbulent flow,heat transfer and mass transfer.In this paper,a three-dimensional simulation of propane pyrolysis reactor tube is performed based on a detailed kinetic radical cracking scheme,combined with a comprehensive rigorous computational fluid dynamics(CFD)model.The eddy-dissipation-concept(EDC)model is introduced to deal with turbulence-chemistry interaction of cracking gas,especially for the multi-step radical kinetics.Considering the high aspect ratio and severe gradient phenomenon,numerical strategies such as grid resolution and refinement,stepping method and relaxation technique at different levels are employed to accelerate convergence.Large scale of radial nonuniformity in the vicinity of the tube wall is investigated.Spatial distributions of each radical reaction rate are first studied,and made it possible to identify the dominant elementary reactions.Additionally,a series of operating conditions including the feedstock feed rate,wall temperature profile and heat flux profile towards the reactor tubes are investigated.The obtained results can be used as scientific guide for further technical retrofit and operation optimization aiming at high conversion and selectivity of pyrolysis process.
基金ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (No.10534010 and No.20673140).
文摘The photodissociation of Br2 was investigated within the near-visible UV absorption band. Based on the potential curves for the ground and low-lying excited states, the optical cross-sections for the discrete transitions of C1^Пu,B^3Пou^+, A^3П1u←X^1∑g+ and their total energy absorption spectrum are derived, and the quantum yield of (Br+Br6*) channel are determined correspondingly. The one-dimensional Landau-Zener model is used to evaluate the behavior of curve crossing during photodissociation. The results indicate that the influence of nonadiabatic mechanism, which may be caused by the electronic-vibrational interplay between the 13 and C states, is negligibly small for the (Br+Br^*) channel. From the Landau-Zener modeling of the observed product recoil parameter β(Br+Br), the best-fit value of the coupling matrix elenment or coupling strength between the diabatic B and C state potentials is obtained.
基金supported by the National Natural Science Foundation of China(Grant Nos.51275114 and 51006093)the Laboratory of Precision Manufacturing Technology in China Academy of Engineering Physics(Grant No.zz13010)the Fundamental Research Funds for the Central Universities,China(Grant No.HIT.NSRIF.2013050)
文摘In the present work we elucidate the thermodynamic mechanisms of femtosecond(fs)laser ablation of amorphous polystyrene by means of molecular dynamics(MD)simulations.The effects of extrinsic parameter of laser pulse intensity and intrinsic parameter of molecular architecture on the laser ablation are further studied.Simulation results show that the laser ablation-induced polymeric material removal is achieved by evaporation from the surface and expansion within the bulk.Furthermore,inter-chain sliding and intra-chain change also play important roles in the microscopic deformation of the material.It is found that both the laser pulse intensity and the arrangement of phenyl groups have significant influence on the fs laser ablation of polystyrene.
基金supported by the National Natural Science Foundation of China (Grant No. 50976035)
文摘Sulfur dioxide (SO2) and nitrogen oxide (NOx) in flue gas can be removed by combining microwave induced catalysis and adsorption on activated carbon. The reaction mechanisms of desulfurization and denitrification by microwave irradiation were analyzed based on the measurement of reaction products. Thermodynamic parameters for desulfurization and denitrification by thermal-carbon reduction were predicted according to the principles of thermodynamics. The experimental results indicated that the desulfurization and denitrification reaction processes include three reaction stages: slow reaction zone, transitional zone and rapid reaction zone. In high temperature zone, activation energies for the reduction of SO2 and nitrogen monoxide (NO) are 30.69 and 24.06 kJ mo1-1, respectively. This study shows that microwave can effectively enhance the removal of pollutants through its heating effect and the induced catalysis.