Based on the volcanic relationship between catalytic activity and key adsorption energies,Pt-Co alloy materials have been widely studied as cathode oxygen reduction reaction(ORR)catalysts in proton exchange membrane f...Based on the volcanic relationship between catalytic activity and key adsorption energies,Pt-Co alloy materials have been widely studied as cathode oxygen reduction reaction(ORR)catalysts in proton exchange membrane fuel cells(PEMFCs)due to their higher active surface area and adjustable D-band energy levels compared to Pt/C.However,how to balance the alloying degree and ORR performance of Pt-Co catalyst remains a great challenge.Herein,we first synthesized a well-dispersed Pt/Co/C precursor by using a mild dimethylamine borane(DMAB)as the reducing agent.The precursor was calcined at high temperature under H_(2)/Ar mixed gas by a secondary reduction strategy to obtain an ordered Pt_(3)Co intermetallic compound nanoparticle catalyst with a high degree of alloying.The optimization of elec-tronic structure due to Pt-Co alloying and the strong metal-carrier interaction ensure the high kinetic activity of the cell membrane electrode.Additionally,the high degree of graphitization increases the electrical conductivity during the reaction.As a result,the activity and stability of the catalyst were significantly improved,with a half-wave potential as high as 0.87 V,which decreased by only 20 mV after 10000 potential cycles.Single-cell tests further validate the high intrinsic activity of the ordered Pt_(3)Co catalyst with mass activity up to 0.67 A mg_(pt)^(-1),exceeding the United States Department of Energy(US DOE)standard(0.44 A mg_(pt)^(-1)),and a rated power of 5.93 W mg_(pt)^(-1).展开更多
Spray evaporation of liquid fuels in a turbulent flow is a common process in various engineering applications such as combustion.Interactions between fuel droplets(discrete phase)and fluid flow(continuous phase)have a...Spray evaporation of liquid fuels in a turbulent flow is a common process in various engineering applications such as combustion.Interactions between fuel droplets(discrete phase)and fluid flow(continuous phase)have a considerable effect on liquid fuel evaporation.In this paper,both the single-and two-phase modeling of liquid fuel injection into a model evaporating chamber are presented.The influences of important issues such as turbulence models,coupling between gas phase and droplets,secondary break-up and air swirling on the current spray simulation are investigated.Accordingly,the shear stress transport turbulence model,Taylor analogy break-up and two-way coupling models are applied to simulate the two-phase flow.Atomization and spray of fuel droplets in hot air are modeled employing an Eulerian-Lagrangian approach.The current results show an acceptable agreement with the experiments.Adjacent the fuel atomizer,bigger droplets are detected near the spray edge and minor droplets are situated in the middle.With increasing the droplets axial position,the droplets diameter decreases with a finite slope.The smaller droplets have a deeper penetration,but their lifetime is smaller and they evaporate sooner.A linear relation between penetration and lifetime of smaller droplets is detected.Maximum droplet penetration and mean axial velocity of gas phase are observed for no air swirling case.The effect of variation of swirl number on the lifetime of droplets is almost negligible.By enhancing the swirl number,the uniformity of droplet size distribution is reduced and some large droplets are formed up in the domain.展开更多
The fuel manifold is an import accessory through which the fuel enters in combustor,after measuring in fuel control system.The component test results of fuel manifolds show that,when the starting fuel supply is given ...The fuel manifold is an import accessory through which the fuel enters in combustor,after measuring in fuel control system.The component test results of fuel manifolds show that,when the starting fuel supply is given and the primary fuel manifold relative unfold pressure is at constant,the adjustment of the secondary fuel manifold turn-on pressure has effects on fuel flow through the secondary fuel manifold and the time of fuel into the combustion chamber.The verification test of the secondary fuel manifold unfold pressure influence on engine starting performance has been conducted,showing that the unfold pressure variation of the secondary fuel manifold has great influence on the engine start performance.The test research results have important guidance and reference meaning for confirming the secondary fuel manifold unfolds pressure.展开更多
In nuclear reactor fuel assemblies, spacer grids are installed among the rod bundles to support the fuel rods and affect the flow field between rods. Mixing vanes, as a swirling device, are set on the upper apex of th...In nuclear reactor fuel assemblies, spacer grids are installed among the rod bundles to support the fuel rods and affect the flow field between rods. Mixing vanes, as a swirling device, are set on the upper apex of the spacer grid. Vortexes produced by mixing vanes move along the axial direction in subchannels and enhance the forced convection heat transfer between the rods and cooling-fluid medium. In this paper, a numerical simulation method was used to investigate vortex motion produced by typical AFA-3G spacer grids in a 5×5-rod bundle by Star-CCM+ software. The shear-stress transport k-ω model was used to simulate turbulence phenomena. A dimensionless parameter, Se, based on the absolute vorticity flux, was reported to specify the intensity of secondary flow. Its physical meaning is the ratio of inertial force to viscous force induced by secondary flow. The results are helpful to take advantage of spacer grids in a much more effective way in pressurized water reactors.展开更多
A triple swirler combustor is considered to be a promising solution for future high temperature rise combustors. The present paper aims to study dilution holes including primary dilution holes and secondary dilution h...A triple swirler combustor is considered to be a promising solution for future high temperature rise combustors. The present paper aims to study dilution holes including primary dilution holes and secondary dilution holes on the performance of a triple swirler combustor. Experimental investigations are conducted at different inlet airflow velocities（40–70 m/s） and combustor overall fuel–air ratio with fixed inlet airflow temperature（473 K） and atmospheric pressure. The experimental results show that the ignition is very difficult with specific performance of high ignition fuel–air ratio when the primary dilution holes are located 0.6H（where H is the liner dome height）downstream the dome, while the other four cases have almost the same ignition performance. The position of primary dilution holes has an effect on lean blowout stability and has a large influence on combustion efficiency. The combustion efficiency is the highest when the primary dilution holes are placed 0.9H downstream the dome among the five different locations.For the secondary dilution holes, the pattern factor of Design A is better than that of Design B.展开更多
基金supported by the National Key Research and Development Program of China(grant No.2022YFB3807500)the National Natural Science Foundation of China(grant No.21922802,22220102003)+1 种基金the Beijing Natural Science Foundation(grant No.JQ19007)“Double-First-Class”construction projects(grant No.XK180301,XK1804-02).
文摘Based on the volcanic relationship between catalytic activity and key adsorption energies,Pt-Co alloy materials have been widely studied as cathode oxygen reduction reaction(ORR)catalysts in proton exchange membrane fuel cells(PEMFCs)due to their higher active surface area and adjustable D-band energy levels compared to Pt/C.However,how to balance the alloying degree and ORR performance of Pt-Co catalyst remains a great challenge.Herein,we first synthesized a well-dispersed Pt/Co/C precursor by using a mild dimethylamine borane(DMAB)as the reducing agent.The precursor was calcined at high temperature under H_(2)/Ar mixed gas by a secondary reduction strategy to obtain an ordered Pt_(3)Co intermetallic compound nanoparticle catalyst with a high degree of alloying.The optimization of elec-tronic structure due to Pt-Co alloying and the strong metal-carrier interaction ensure the high kinetic activity of the cell membrane electrode.Additionally,the high degree of graphitization increases the electrical conductivity during the reaction.As a result,the activity and stability of the catalyst were significantly improved,with a half-wave potential as high as 0.87 V,which decreased by only 20 mV after 10000 potential cycles.Single-cell tests further validate the high intrinsic activity of the ordered Pt_(3)Co catalyst with mass activity up to 0.67 A mg_(pt)^(-1),exceeding the United States Department of Energy(US DOE)standard(0.44 A mg_(pt)^(-1)),and a rated power of 5.93 W mg_(pt)^(-1).
文摘Spray evaporation of liquid fuels in a turbulent flow is a common process in various engineering applications such as combustion.Interactions between fuel droplets(discrete phase)and fluid flow(continuous phase)have a considerable effect on liquid fuel evaporation.In this paper,both the single-and two-phase modeling of liquid fuel injection into a model evaporating chamber are presented.The influences of important issues such as turbulence models,coupling between gas phase and droplets,secondary break-up and air swirling on the current spray simulation are investigated.Accordingly,the shear stress transport turbulence model,Taylor analogy break-up and two-way coupling models are applied to simulate the two-phase flow.Atomization and spray of fuel droplets in hot air are modeled employing an Eulerian-Lagrangian approach.The current results show an acceptable agreement with the experiments.Adjacent the fuel atomizer,bigger droplets are detected near the spray edge and minor droplets are situated in the middle.With increasing the droplets axial position,the droplets diameter decreases with a finite slope.The smaller droplets have a deeper penetration,but their lifetime is smaller and they evaporate sooner.A linear relation between penetration and lifetime of smaller droplets is detected.Maximum droplet penetration and mean axial velocity of gas phase are observed for no air swirling case.The effect of variation of swirl number on the lifetime of droplets is almost negligible.By enhancing the swirl number,the uniformity of droplet size distribution is reduced and some large droplets are formed up in the domain.
文摘The fuel manifold is an import accessory through which the fuel enters in combustor,after measuring in fuel control system.The component test results of fuel manifolds show that,when the starting fuel supply is given and the primary fuel manifold relative unfold pressure is at constant,the adjustment of the secondary fuel manifold turn-on pressure has effects on fuel flow through the secondary fuel manifold and the time of fuel into the combustion chamber.The verification test of the secondary fuel manifold unfold pressure influence on engine starting performance has been conducted,showing that the unfold pressure variation of the secondary fuel manifold has great influence on the engine start performance.The test research results have important guidance and reference meaning for confirming the secondary fuel manifold unfolds pressure.
文摘In nuclear reactor fuel assemblies, spacer grids are installed among the rod bundles to support the fuel rods and affect the flow field between rods. Mixing vanes, as a swirling device, are set on the upper apex of the spacer grid. Vortexes produced by mixing vanes move along the axial direction in subchannels and enhance the forced convection heat transfer between the rods and cooling-fluid medium. In this paper, a numerical simulation method was used to investigate vortex motion produced by typical AFA-3G spacer grids in a 5×5-rod bundle by Star-CCM+ software. The shear-stress transport k-ω model was used to simulate turbulence phenomena. A dimensionless parameter, Se, based on the absolute vorticity flux, was reported to specify the intensity of secondary flow. Its physical meaning is the ratio of inertial force to viscous force induced by secondary flow. The results are helpful to take advantage of spacer grids in a much more effective way in pressurized water reactors.
基金supported by Funding for Outstanding Doctoral Dissertation in NUAA (No. BCXJ 14-01)Funding of Jiangsu Innovation Program for Graduate Education (No. CXLX12_0169)
文摘A triple swirler combustor is considered to be a promising solution for future high temperature rise combustors. The present paper aims to study dilution holes including primary dilution holes and secondary dilution holes on the performance of a triple swirler combustor. Experimental investigations are conducted at different inlet airflow velocities（40–70 m/s） and combustor overall fuel–air ratio with fixed inlet airflow temperature（473 K） and atmospheric pressure. The experimental results show that the ignition is very difficult with specific performance of high ignition fuel–air ratio when the primary dilution holes are located 0.6H（where H is the liner dome height）downstream the dome, while the other four cases have almost the same ignition performance. The position of primary dilution holes has an effect on lean blowout stability and has a large influence on combustion efficiency. The combustion efficiency is the highest when the primary dilution holes are placed 0.9H downstream the dome among the five different locations.For the secondary dilution holes, the pattern factor of Design A is better than that of Design B.
