Energetic Semiconductor bridge(ESCB)based on reactive multilayered films(RMFs)has a promising application in the miniature and intelligence of initiator and pyrotechnics device.Understanding the ignition enhancement m...Energetic Semiconductor bridge(ESCB)based on reactive multilayered films(RMFs)has a promising application in the miniature and intelligence of initiator and pyrotechnics device.Understanding the ignition enhancement mechanism of RMFs on semiconductor bridge(SCB)during the ignition process is crucial for the engineering and practical application of advanced initiator and pyrotechnics devices.In this study,a one-dimensional(1D)gas-solid two-phase flow ignition model was established to study the ignition process of ESCB to charge particles based on the reactivity of Al/MoO_(3) RMFs.In order to fully consider the coupled exothermic between the RMFs and the SCB plasma during the ignition process,the heat release of chemical reaction in RMFs was used as an internal heat source in this model.It is found that the exothermal reaction in RMFs improved the ignition performance of SCB.In the process of plasma rapid condensation with heat release,the product of RMFs enhanced the heat transfer process between the gas phase and the solid charge particle,which accelerated the expansion of hot plasma,and heated the solid charge particle as well as gas phase region with low temperature.In addition,it made up for pressure loss in the gas phase.During the plasma dissipation process,the exothermal chemical reaction in RMFs acted as the main heating source to heat the charge particle,making the surface temperature of the charge particle,gas pressure,and gas temperature rise continuously.This result may yield significant advantages in providing a universal ignition model for miniaturized ignition devices.展开更多
The mixing characteristics of particles such as dredged sediment of variable size discharged into cross flow are studied by a 3D numerical modal, which is developed to model the particle-fluid two-phase flow. The Eule...The mixing characteristics of particles such as dredged sediment of variable size discharged into cross flow are studied by a 3D numerical modal, which is developed to model the particle-fluid two-phase flow. The Eulerian method with the modified k- ε parameterization of turbulence for the fluid phase is used to solve fluid phase, while a Lagrangian method for the sohd phase （particles）, both the processes are coupled through the momentmn sources. In the model the wake turbulence induced by particles has been included as additional source term in the k - ε model; and the variable drift velocities of the particles are treated efficiently by the Lagrangian method in which the particles are tracked explicitly and the diffusion process is approximated by a random walk model. The hydrodynamic behavior of dumping a cloud of particles is governed by the total buoyancy of the cloud, the drag force on each particle and the velocity of cross-flow. The computed results show a roughly linear relationship between the displacement of the frontal position and the longitudi- nal width of the particle cloud. The particle size in the cloud and the velocity of cross flow dominate the flow behavior. The computed results are compared with the results of laboratory experiments and satisfactory agreement is obtained.展开更多
Recent developments in the utilization of microfluidic chips(MFCs) have shown their potential utility in multiphase organic synthesis by enabling efficient organic reactions in flow chemistry. However, MFCs technology...Recent developments in the utilization of microfluidic chips(MFCs) have shown their potential utility in multiphase organic synthesis by enabling efficient organic reactions in flow chemistry. However, MFCs technology has been wandering in the laboratory of small dose synthetic routes, which is limited to the level of "tiny" fluid flux. To address this issue, we herein report the first case of the chips with highthroughput 3D channels produced by femtosecond laser being used to create a time-saving, cost-effective and risk-free approach suitable for large-scale flow synthesis. Several multiphase reactions have been successfully prepared on demand in our designed flow synthesis system containing 3D MFCs: 1) benzyl alcohol was converted to benzaldehyde in 3 min with a yield of 97.50% by liquid-liquid two-phase transfer catalytic oxidation;2) organozinc reagents and α-cyano carbonyl carbon compounds were synthesized by solid-liquid two-phase metal insertion reaction in 7 min, and the yield was up to 100%;3) benzoic acid was synthesized by gas-liquid two-phase carboxylation reaction in 2.8 s with a yield of 96%. Significant gains in production rate result from the effective scaling of flow reactors from microliters per hour in MFCs to intermediate milliliters per minute without affecting mass transport performance. Meanwhile,our 3D MFCs show excellent mass and heat transfer efficiency in large-scale industrial units, breaking through the bottleneck in this field. As a result, it is possible to imagine the creation of a new, streamlined flow synthetic technique via MFCs for green multiphase organic synthesis.展开更多
A new model, which involves viscous and multi-phase effects, was given to study cavitating flows. A local compressible model was established by introducing a density-pressure function to account for the two-phase flow...A new model, which involves viscous and multi-phase effects, was given to study cavitating flows. A local compressible model was established by introducing a density-pressure function to account for the two-phase flow of water/vapor and the transition from one phase to the other. An algorithm for calculating variable-density N-S equations of cavitating flow problem was put forward. The present method yields reasonable results for both steady and unsteady cavitating flows in 2D and 3D cases. The numerical results of unsteady character of cavitating flows around hydrofoils coincide well with experimental data. It indicates the feasibility to apply this method to a variety of cavitating flows of practical problems.展开更多
In this paper a numerical investigation has been presented on the stall mechanism of a highly loaded Single Stage Low Speed Fan designed for the research test facility to be installed at North Western Polytechnic Univ...In this paper a numerical investigation has been presented on the stall mechanism of a highly loaded Single Stage Low Speed Fan designed for the research test facility to be installed at North Western Polytechnic University (NWPU) Xi’an, China. The results presented are for the design point, near stall and just stall operating conditions at design speed. Design point studies have been found to be an indicative of stall area. Unsteady method of domain scaling has been used to compute the results at near stall and just stall conditions. It has been found that unlike the conventional tip leakage flow of the rotor, stator hub section is mainly responsible for the stall of the fan. The flow mechanism has been discussed with correlation to the design variables and previous investigations. Commercial CFD code NUMECA FINE/Turbo has been used for computations; results have been compared with results obtained from commercial CFD code ANSYS-CFX. The loss prediction of latter code is conservative than the former. The stall mechanism predicted by both codes is analogous.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.22275092,52102107 and 52372084)the Fundamental Research Funds for the Central Universities(Grant No.30923010920)。
文摘Energetic Semiconductor bridge(ESCB)based on reactive multilayered films(RMFs)has a promising application in the miniature and intelligence of initiator and pyrotechnics device.Understanding the ignition enhancement mechanism of RMFs on semiconductor bridge(SCB)during the ignition process is crucial for the engineering and practical application of advanced initiator and pyrotechnics devices.In this study,a one-dimensional(1D)gas-solid two-phase flow ignition model was established to study the ignition process of ESCB to charge particles based on the reactivity of Al/MoO_(3) RMFs.In order to fully consider the coupled exothermic between the RMFs and the SCB plasma during the ignition process,the heat release of chemical reaction in RMFs was used as an internal heat source in this model.It is found that the exothermal reaction in RMFs improved the ignition performance of SCB.In the process of plasma rapid condensation with heat release,the product of RMFs enhanced the heat transfer process between the gas phase and the solid charge particle,which accelerated the expansion of hot plasma,and heated the solid charge particle as well as gas phase region with low temperature.In addition,it made up for pressure loss in the gas phase.During the plasma dissipation process,the exothermal chemical reaction in RMFs acted as the main heating source to heat the charge particle,making the surface temperature of the charge particle,gas pressure,and gas temperature rise continuously.This result may yield significant advantages in providing a universal ignition model for miniaturized ignition devices.
基金This work was supported by a grant fromthe Research Grant Council of the Hong Kong Special Administrative Region(Project No5033/98E)
文摘The mixing characteristics of particles such as dredged sediment of variable size discharged into cross flow are studied by a 3D numerical modal, which is developed to model the particle-fluid two-phase flow. The Eulerian method with the modified k- ε parameterization of turbulence for the fluid phase is used to solve fluid phase, while a Lagrangian method for the sohd phase （particles）, both the processes are coupled through the momentmn sources. In the model the wake turbulence induced by particles has been included as additional source term in the k - ε model; and the variable drift velocities of the particles are treated efficiently by the Lagrangian method in which the particles are tracked explicitly and the diffusion process is approximated by a random walk model. The hydrodynamic behavior of dumping a cloud of particles is governed by the total buoyancy of the cloud, the drag force on each particle and the velocity of cross-flow. The computed results show a roughly linear relationship between the displacement of the frontal position and the longitudi- nal width of the particle cloud. The particle size in the cloud and the velocity of cross flow dominate the flow behavior. The computed results are compared with the results of laboratory experiments and satisfactory agreement is obtained.
基金supported by the Shanghai Municipal Science and Technology Major Project (“Beyond Limits manufacture”)。
文摘Recent developments in the utilization of microfluidic chips(MFCs) have shown their potential utility in multiphase organic synthesis by enabling efficient organic reactions in flow chemistry. However, MFCs technology has been wandering in the laboratory of small dose synthetic routes, which is limited to the level of "tiny" fluid flux. To address this issue, we herein report the first case of the chips with highthroughput 3D channels produced by femtosecond laser being used to create a time-saving, cost-effective and risk-free approach suitable for large-scale flow synthesis. Several multiphase reactions have been successfully prepared on demand in our designed flow synthesis system containing 3D MFCs: 1) benzyl alcohol was converted to benzaldehyde in 3 min with a yield of 97.50% by liquid-liquid two-phase transfer catalytic oxidation;2) organozinc reagents and α-cyano carbonyl carbon compounds were synthesized by solid-liquid two-phase metal insertion reaction in 7 min, and the yield was up to 100%;3) benzoic acid was synthesized by gas-liquid two-phase carboxylation reaction in 2.8 s with a yield of 96%. Significant gains in production rate result from the effective scaling of flow reactors from microliters per hour in MFCs to intermediate milliliters per minute without affecting mass transport performance. Meanwhile,our 3D MFCs show excellent mass and heat transfer efficiency in large-scale industrial units, breaking through the bottleneck in this field. As a result, it is possible to imagine the creation of a new, streamlined flow synthetic technique via MFCs for green multiphase organic synthesis.
文摘A new model, which involves viscous and multi-phase effects, was given to study cavitating flows. A local compressible model was established by introducing a density-pressure function to account for the two-phase flow of water/vapor and the transition from one phase to the other. An algorithm for calculating variable-density N-S equations of cavitating flow problem was put forward. The present method yields reasonable results for both steady and unsteady cavitating flows in 2D and 3D cases. The numerical results of unsteady character of cavitating flows around hydrofoils coincide well with experimental data. It indicates the feasibility to apply this method to a variety of cavitating flows of practical problems.
文摘In this paper a numerical investigation has been presented on the stall mechanism of a highly loaded Single Stage Low Speed Fan designed for the research test facility to be installed at North Western Polytechnic University (NWPU) Xi’an, China. The results presented are for the design point, near stall and just stall operating conditions at design speed. Design point studies have been found to be an indicative of stall area. Unsteady method of domain scaling has been used to compute the results at near stall and just stall conditions. It has been found that unlike the conventional tip leakage flow of the rotor, stator hub section is mainly responsible for the stall of the fan. The flow mechanism has been discussed with correlation to the design variables and previous investigations. Commercial CFD code NUMECA FINE/Turbo has been used for computations; results have been compared with results obtained from commercial CFD code ANSYS-CFX. The loss prediction of latter code is conservative than the former. The stall mechanism predicted by both codes is analogous.
