By conjugating features of combustion gas jetting flows of the solid-rocket and using mathematical methods, a numerical scheme is systematically derived based on Harten′s standard TVD scheme, which fits for the flow ...By conjugating features of combustion gas jetting flows of the solid-rocket and using mathematical methods, a numerical scheme is systematically derived based on Harten′s standard TVD scheme, which fits for the flow with high temperature, pressure and velocity. The rational calculation formula of pressure partial derivation is also given out. By using the chemical kinetics knowledge, problems of multi-component and finite rate chemical reaction contained in combustion gas of the rocket flow field are discussed. The method for solving the mass source term of chemical reaction is clarified. Taking 9 reaction equations with 12 components as an example and utilizing the established calculation program, the free jetting flow field of the rocket is simulated. Numerical results show the correctness of the numerical scheme.展开更多
This article addresses the magnetohydrodynamics(MHD) flow of a third grade fluid over an exponentially stretching sheet. Analysis is carried out in the presence of first order chemical reaction. Both cases of construc...This article addresses the magnetohydrodynamics(MHD) flow of a third grade fluid over an exponentially stretching sheet. Analysis is carried out in the presence of first order chemical reaction. Both cases of constructive and destructive chemical reactions are reported. Convergent solutions of the resulting differential systems are presented in series forms. Characteristics of various sundry parameters on the velocity, concentration, skin friction and local Sherwood number are analyzed and discussed.展开更多
Microchannel reactors are commonly used in micro-chemical technology. The performance of microreactors is greatly affected by the velocity field in the microchannel. The flow field is disturbed by the cylindrical etch...Microchannel reactors are commonly used in micro-chemical technology. The performance of microreactors is greatly affected by the velocity field in the microchannel. The flow field is disturbed by the cylindrical etch holes caused by air dust on the microchannel surface during its processing procedure. In this approach, a two-dimensional computational fluid dynamics （CFD） model is put forward to study the effect of etch holes on flow field. The influenced area of single or two concave etch holes is studied for the case of laminar flow. The hole diameter, the Reynolds number and the distance between the center of holes are found to have influences on the flow field. Numerical results indicate that the effects of etch hole on the flow field should be evaluated and the way of choosing the economic class of cleanroom for microreactor manufacture is presented.展开更多
One of the most important and effective hardware elements for improvement of efficiency and power density of proton exchange membrane fuel cells is the flow field plate. The design and the pattern of the flow field pl...One of the most important and effective hardware elements for improvement of efficiency and power density of proton exchange membrane fuel cells is the flow field plate. The design and the pattern of the flow field plate have a considerable effect on the effectiveness of mass transport as well as on the electrochemical reactions inside the cell. The configuration of the flow field plate aims at ensuring a low pressure-drop over all channels in the stack. In this work, a FPFFP （fractal parallel flow field plate）, with bio-inspired configuration by insertion of fractals in a classic PFFP （parallel flow field plate）, is proposed, increasing the flow area of the hydrogen at anode side without increasing the section＇s area of the flow field plate. By simulating was observed that, the use of channels in fractal shape can increase the hydrogen flow area without occuring pressure loss in the cell. The fluid dynamic behavior in the FPFFP at smaller scales was replicated in the same plate, with better advantage of the active area of the electrode. Increasing the hydrogen flow area without causing pressure loss could be a good tactic to increase the power density of fuel cells, and consequently improving the cell performance.展开更多
A hybrid rocket can be used in various applications and is an attractive propulsion system. However, serious erosion of nozzles is common in motor firing operations, which could restrict the application of hybrid rock...A hybrid rocket can be used in various applications and is an attractive propulsion system. However, serious erosion of nozzles is common in motor firing operations, which could restrict the application of hybrid rocket motors. Usually, the serious erosion is attributed to the high concentration of oxidizing species in hybrid motors, while the details of flowfields in the motors are not paid special attention to. In this paper, first the thermochemical erosion of C/C nozzle is simulated coupled with the flowfields in a 98% H2O2/hydroxyl-terminated polybutadiene（HTPB） hybrid rocket motor. The simulation is made on a typical axisymmetric motor, including a pre-combustion chamber, an aft-combustion chamber and nozzle structures. Thermochemica reactions of H2 O, CO2, OH, O and O2 with C are taken into account. Second, the change of flowfields due to fuel regression during motor firing operations is considered. Nozzle erosion in different flowfields is evaluated. Third, the results of nozzle erosion in the coupled simulation are compared with those under uniform and chemical equilibrium flow and motor firing test results. The results of simulation and firing tests indicate that the thermochemical erosion of nozzles in hybrid motors should be calculated coupled with flowfields in the motor. In uniform and chemical equilibrium flowfields, the erosion rate is overestimated. The diffusion flame in hybrid motors protects the nozzle surface from the injected oxidizer and high temperature products in flowfields, leading to a relatively fuel-rich environment above the nozzle. The influence of OH and the geometry of motor should also be considered in the evaluation of nozzle erosion in hybrid motors.展开更多
文摘By conjugating features of combustion gas jetting flows of the solid-rocket and using mathematical methods, a numerical scheme is systematically derived based on Harten′s standard TVD scheme, which fits for the flow with high temperature, pressure and velocity. The rational calculation formula of pressure partial derivation is also given out. By using the chemical kinetics knowledge, problems of multi-component and finite rate chemical reaction contained in combustion gas of the rocket flow field are discussed. The method for solving the mass source term of chemical reaction is clarified. Taking 9 reaction equations with 12 components as an example and utilizing the established calculation program, the free jetting flow field of the rocket is simulated. Numerical results show the correctness of the numerical scheme.
文摘This article addresses the magnetohydrodynamics(MHD) flow of a third grade fluid over an exponentially stretching sheet. Analysis is carried out in the presence of first order chemical reaction. Both cases of constructive and destructive chemical reactions are reported. Convergent solutions of the resulting differential systems are presented in series forms. Characteristics of various sundry parameters on the velocity, concentration, skin friction and local Sherwood number are analyzed and discussed.
基金Supported by the National Natural Science Foundation of China （20676093）.
文摘Microchannel reactors are commonly used in micro-chemical technology. The performance of microreactors is greatly affected by the velocity field in the microchannel. The flow field is disturbed by the cylindrical etch holes caused by air dust on the microchannel surface during its processing procedure. In this approach, a two-dimensional computational fluid dynamics （CFD） model is put forward to study the effect of etch holes on flow field. The influenced area of single or two concave etch holes is studied for the case of laminar flow. The hole diameter, the Reynolds number and the distance between the center of holes are found to have influences on the flow field. Numerical results indicate that the effects of etch hole on the flow field should be evaluated and the way of choosing the economic class of cleanroom for microreactor manufacture is presented.
文摘One of the most important and effective hardware elements for improvement of efficiency and power density of proton exchange membrane fuel cells is the flow field plate. The design and the pattern of the flow field plate have a considerable effect on the effectiveness of mass transport as well as on the electrochemical reactions inside the cell. The configuration of the flow field plate aims at ensuring a low pressure-drop over all channels in the stack. In this work, a FPFFP （fractal parallel flow field plate）, with bio-inspired configuration by insertion of fractals in a classic PFFP （parallel flow field plate）, is proposed, increasing the flow area of the hydrogen at anode side without increasing the section＇s area of the flow field plate. By simulating was observed that, the use of channels in fractal shape can increase the hydrogen flow area without occuring pressure loss in the cell. The fluid dynamic behavior in the FPFFP at smaller scales was replicated in the same plate, with better advantage of the active area of the electrode. Increasing the hydrogen flow area without causing pressure loss could be a good tactic to increase the power density of fuel cells, and consequently improving the cell performance.
文摘A hybrid rocket can be used in various applications and is an attractive propulsion system. However, serious erosion of nozzles is common in motor firing operations, which could restrict the application of hybrid rocket motors. Usually, the serious erosion is attributed to the high concentration of oxidizing species in hybrid motors, while the details of flowfields in the motors are not paid special attention to. In this paper, first the thermochemical erosion of C/C nozzle is simulated coupled with the flowfields in a 98% H2O2/hydroxyl-terminated polybutadiene（HTPB） hybrid rocket motor. The simulation is made on a typical axisymmetric motor, including a pre-combustion chamber, an aft-combustion chamber and nozzle structures. Thermochemica reactions of H2 O, CO2, OH, O and O2 with C are taken into account. Second, the change of flowfields due to fuel regression during motor firing operations is considered. Nozzle erosion in different flowfields is evaluated. Third, the results of nozzle erosion in the coupled simulation are compared with those under uniform and chemical equilibrium flow and motor firing test results. The results of simulation and firing tests indicate that the thermochemical erosion of nozzles in hybrid motors should be calculated coupled with flowfields in the motor. In uniform and chemical equilibrium flowfields, the erosion rate is overestimated. The diffusion flame in hybrid motors protects the nozzle surface from the injected oxidizer and high temperature products in flowfields, leading to a relatively fuel-rich environment above the nozzle. The influence of OH and the geometry of motor should also be considered in the evaluation of nozzle erosion in hybrid motors.
