Magnetic field design is essential for the operation of Hall thrusters.This study focuses on utilizing a genetic algorithm to optimize the magnetic field configuration of SPT70.A 2D hybrid PIC-DSMC and channel-wall er...Magnetic field design is essential for the operation of Hall thrusters.This study focuses on utilizing a genetic algorithm to optimize the magnetic field configuration of SPT70.A 2D hybrid PIC-DSMC and channel-wall erosion model are employed to analyze the plume divergence angle and wall erosion rate,while a Farady probe measurement and laser profilometry system are set up to verify the simulation results.The results demonstrate that the genetic algorithm contributes to reducing the divergence angle of the thruster plumes and alleviating the impact of high-energy particles on the discharge channel wall,reducing the erosion by 5.5%and 2.7%,respectively.Further analysis indicates that the change from a divergent magnetic field to a convergent magnetic field,combined with the upstream shift of the ionization region,contributes to the improving the operation of the Hall thruster.展开更多
To advance the performance of solid oxide fuel cells(SOFCs),this work proposes a novel biomimetic flow field architecture inspired by the geometric arrangement of sunflower florets.Drawing on natural principles of opt...To advance the performance of solid oxide fuel cells(SOFCs),this work proposes a novel biomimetic flow field architecture inspired by the geometric arrangement of sunflower florets.Drawing on natural principles of optimal spatial distribution,a multi-physics simulation model of the resulting Sunflower Bionic Flow Field(SBFF)was developed.Building upon this foundation,an enhanced configuration was introduced by integrating an annular channel,yielding a modified variant referred to as Modified Sunflower Bionic Flow Field(MSBFF).For comparative purposes,a conventional Traditional Parallel Flow Field(TPFF)was also analyzed under identical conditions.Simulation results underscore the superior gas distribution performance of the bionic configurations.Both SBFF and MSBFF significantly improved the homogeneity of reactant gas molar concentration throughout the flow domain.Relative to the TPFF,the SBFF achieved a 13.32%increase in current density,while the MSBFF reached an enhancement of 15.09%.Correspondingly,peak power densities rose by 14.07%and 16.55%,respectively.Furthermore,these bio-inspired structures contributed to improved thermal regulation,as evidenced by a reduction in average electrolyte temperature by 3.22%for the SBFF and 2.92%for the MSBFF.To further optimize performance,the influence of Fibonacci spiral channel count within the MSBFF design was systematically investigated.Results reveal a strong positive correlation between the number of spiral channels and electrochemical output.In particular,the MSBFF with 16 spiral channels(MSBFF-16)demonstrated the most favorable electrical and thermal characteristics.At an operating voltage of 0.7 V,MSBFF-16 exhibited a current density increase of 1.27%and 0.94%over MSBFF and MSBFF-12,respectively.Likewise,peak power density improved by 2.69%and 1.67%.Finally,the study examined the impact of varying inlet mass fractions of oxygen and hydrogen on SOFC performance.Distinct trends were observed:increasing the oxygen mass fraction markedly enhanced heat transfer and current density,while greater hydrogen mass fractions significantly boosted fuel utilization.These findings highlight the crucial role of reactant composition and flow field topology in governing the electrochemical and thermal efficiency of SOFC systems.展开更多
The shape optimization is studied by adopting the domain integrated method which is based on the calculus of variations during the shape design sensitivity analysis. A new method of improving the efficiency of the de...The shape optimization is studied by adopting the domain integrated method which is based on the calculus of variations during the shape design sensitivity analysis. A new method of improving the efficiency of the design velocity field analysis and the quality of the finite element method (FEM) mesh is put forward. The sensitivity analysis which is based on the calculus of variations is used in the shape optimization. The design velocity field is solved by Herrmann method. An example shows that both the quality of the FEM mesh and the efficiency of the computing of the design velocity field are improved by Herrmann method. So the effect and the efficiency of the shape optimization are guaranteed. If using sensitivity analysis which is based on the calculus of variations in the shape optimization, the sensitivity analysis can be a relatively independent module. The efficiency of computing the design velocity field and the quality of mesh will be improved by using Herrmann method.展开更多
Hall thrusters with large height-radius ratio,owing to their unique advantages in compactness,lightweight,and high performance,have progressively emerged as a preferred choice for diverse space propulsion applications...Hall thrusters with large height-radius ratio,owing to their unique advantages in compactness,lightweight,and high performance,have progressively emerged as a preferred choice for diverse space propulsion applications in the future.However,the amplification of the annular effect in structures with a large height-radius ratio poses a practical problem of plume over-focusing,which seriously restricts the further improvement of Hall thruster performance and the extension of its life.In this study,the formation mechanism of over-focused plume is deeply investigated,and it is ascertained that an intensified radial electric field directed towards the inner wall within the channel serves as a key contributing factor.This phenomenon is fundamentally attributed to structural characteristics of large height-radius ratio that induce pronounced inward inclination of field lines within strong magnetic field zone.Based on this,the design concept of focused magnetic field is proposed,wherein straight magnetic field lines are established within the strong magnetic field zone to generate a quasi-axial accelerating electric field.Simultaneously,the symmetrical magnetic field inside the channel ensures ionization concentration near the channel center,thereby achieving optimal matching between the ionization zone and accelerating field.Experimental results demonstrate that employing a focused magnetic field significantly reduces the divergence half-angle of the plume and yields an excellently barrel-shaped focusing plume morphology in HEP-1350PM.Consequently,the total efficiency of the thruster surpasses 60%,while erosion belt on the inner wall is shortened by nearly 50%.These advancements effectively enhance thruster performance and prolong its operational lifespan.This study can not only resolve practical problems associated with plume over-focusing,but also provide a fundamental guiding principle for magnetic field design of Hall thrusters.展开更多
This paper presents the preliminary design of poloidal field power supply system of HT-7U super-conducting tokamak. With an emphasis on AC/DC power converter, DC circuit breaker, quench protection, harmonic suppressio...This paper presents the preliminary design of poloidal field power supply system of HT-7U super-conducting tokamak. With an emphasis on AC/DC power converter, DC circuit breaker, quench protection, harmonic suppression and static var. compensation, and AC power system, the design principle and features are introduced, the design scheme and R & D progress are described, the simulation studies and laboratory test are presented too.展开更多
Interwell connectivities are fundamental parameters required to manage waterfloods in oil reservoirs. Data-driven models, such as the capacitance-resistance model （CRM）, are fast tools to estimate these parameters f...Interwell connectivities are fundamental parameters required to manage waterfloods in oil reservoirs. Data-driven models, such as the capacitance-resistance model （CRM）, are fast tools to estimate these parameters from time-correlations of input （injection rates） and output （production rates） signals. Noise and structure of the input time-series impose limits on the information that can be extracted from a given data-set. This work uses the CRM to study general prescriptions for the design of input signals that enhance the information content of injection/production data in the estimation of well-to-well interactions. Numerical schemes and general features of the optimal input signal strategy are derived for this problem.展开更多
HT7U is a large fusion experimental device. It will be built in the Institute of Plasma Physics of Chinese Academy of Sciences. The mission of HT-7U is to develop the scientific basis for a continuously operating toka...HT7U is a large fusion experimental device. It will be built in the Institute of Plasma Physics of Chinese Academy of Sciences. The mission of HT-7U is to develop the scientific basis for a continuously operating tokama-k fusion reactor. This paper describes only a toroidal field (TF) superconducting magnet system of HT7U. In this paper, design criteria of conductor and stability analysis, coil winding and support structure design of magnet system, mechanical calculation and stress analysis, heat load evaluation are given.展开更多
The design of the poloidal field （PF） system includes the ohmic heating field system and the equilibrium （EQ） field system, and is the basis for the design of a magnetic confinement fusion device. A coupling betwe...The design of the poloidal field （PF） system includes the ohmic heating field system and the equilibrium （EQ） field system, and is the basis for the design of a magnetic confinement fusion device. A coupling between the poloidal and plasma currents, especially the eddy current in the stabilizing shell, yields design difficulties. The effects of the eddy current in the stabilizing shell on the poloidal magnetic field also cannot be ignored. A new PF system design is thus proposed. By using a low-μ material （μ = 0.001, ε = 1） instead of a conductive shell, an electromagnetic model is established that can provide a continuous eddy current distribution on the conductive shell. In this model, a 3D time-domain problem with shells translates into a 2D magnetostatic problem, and the accuracy of the calculation is improved. Based on these current distributions, we design the PF system and analyze how the EQ coils and conductive shell affect the plasma EQ when the plasma ramps up. To meet the mainframe design requirements and achieve an efficient power-supply design, the position and connection of the poloidal coils are optimized further.展开更多
The HT-7U superconducting tokamak is an advanced steady-state plasma physics experimental device to be built in the Institute of Plasma Physics, the Chinese Academy of Sciences (IPP-CAS). The plasma current is 1 MA an...The HT-7U superconducting tokamak is an advanced steady-state plasma physics experimental device to be built in the Institute of Plasma Physics, the Chinese Academy of Sciences (IPP-CAS). The plasma current is 1 MA and the major and minor radius are 1.78 m and 0.4m respectively, with an elongation of 1.85. The preliminary engineering design of the poloidal field (PF) and toroidal field (TF) magnet systems have been done. The PF system is composed of twelve superconducting coils located symmetrically about the equator plane. The central solenoid (CS) assembly is formed by six coils. The TF system consists of 16 superconducting coils. The NbTi cable-in-conduit conductor or (CICC) cooled by a supercritical helium at 4.5 K is chosen as a superconductor for all of the PF and TF coils. At this temperature, the peak magnetic field on the PF magnets is about 4.51 T .The maximum volt-second capacity and the duration of plasma inductive discharge are about 10 Vs and 10 seconds respectively. The stray field in plasma initial region is quite low ( 1.5× 10 -3 T). The magnetic field on the TF magnet is 5.8 T while the toroidal field at the center of the device (R = 1.7 m) is 3.5 T and the ripple of the TF is less than 0.62% at the outer plasma surface (R = 2.1 m). All of the PF and TF magnets are stable during all modes of operation including the plasma disruption. The final design of the PF system is the result of an iterative process involving the use of equilibrium code EQT, magnetic code EFFI, and other codes, which have been developed by our designing group.展开更多
Two design axioms and axiomatic approach were discussed. As an example of application, design process of a new style single prop was illustrated in term of axi- oms.
In the paper the three-dimensional flow fields are numerically simulated in the vertical-shaft mechanical mix tank of a water treatment plant by means of FLUENT software based on the method of Computational Fluid Dyna...In the paper the three-dimensional flow fields are numerically simulated in the vertical-shaft mechanical mix tank of a water treatment plant by means of FLUENT software based on the method of Computational Fluid Dynamics (CFD). The influences of design parameters on flow fields and the mixing effect are analyzed. Firstly,the prediction capability of the turbulence model adopted in simulations is evaluated. And then,the mesh independence is checked up. Finally,the flow fields in various dimensionless blade diameters and dimensionless shaft spans are numerically simulated respectively. The results have shown that the numerical simulation method based on CFD is a feasible assistance for the optimal designs of mixers. Moreover,the optimal design of the blade diameter should take into account both the flow field and the power consumption. The optimization of the shaft span is to achieve a relatively even distribution of the flow field without any rupture. With the consideration of an optimal design,the dimensionless blade diameter and dimensionless shaft span should be 0.45 and 0.57 respectively in the case.展开更多
This paper presents quiet zone design using ultrasonic transducers for local active control in pure tone diffuse fields. Most of researches in local active noise control used conventional loudspeakers for the secondar...This paper presents quiet zone design using ultrasonic transducers for local active control in pure tone diffuse fields. Most of researches in local active noise control used conventional loudspeakers for the secondary sources to produce quiet zones. Recently ultrasonic transducers have been used for the secondary sources to control the plane wave in active noise control. However there is no research related to active noise control in diffuse fields using ultrasonic transducers. Therefore this study uses ultrasonic transducers for the secondary sources to control the diffuse fields. The quiet zone produced using ultrasonic transducers in single tone diffuse fields has been analyzed through simulations in this work. The results showed that quiet zones created using ultrasonic transducers were larger than those created using conventional loudspeakers. This is due to the fact that the audible sound pressure produced by the ultrasonic transducers decays slowly with the distance. Therefore the secondary field created by an ultrasonic transducer could fit the primary field better and the larger zone of quiet could be obtained using the ultrasonic transducer. Also the audible sound produced by the ultrasonic transducers is directional;therefore the sound pressure amplification outside the quiet zones was lower.展开更多
Performance of the proton exchange membrane fuel cell(PEMFC)is appreciably affected by the channel geometry.The branching structure of a plant leaf and human lung is an efficient network to distribute the nutrients in...Performance of the proton exchange membrane fuel cell(PEMFC)is appreciably affected by the channel geometry.The branching structure of a plant leaf and human lung is an efficient network to distribute the nutrients in the respective systems.The same nutrient transport system can be mimicked in the flow channel design of a PEMFC,to aid even reactant distribution and better water management.In this work,the effect of bio-inspired flow field designs such as lung and leaf channel design bipolar plates,on the performance of a PEMFC was examined experimentally at various operating conditions.A PEMFC of 49 cm2 area,with a Nafion 212 membrane with a 40%catalyst loading of 0.4 mg·cm-2 on the anode side and also 0.6 mg·cm-2 on the cathode side is assembled by incorporating the bio-inspired channel bipolar plate,and was tested on a programmable fuel-cell test station.The impact of the working parameters like reactants’relative humidity(RH),back pressure and fuel cell temperature on the performance of the fuel cell was examined;the operating pressure remains constant at 0.1 MPa.It was observed that the best performance was attained at a back pressure of 0.3 MPa,75°C operating temperature and 100%RH.The three flow channels were also compared at different operating pressures ranging from 0.1 MPa to 0.3 MPa,and the other parameters such as operating temperature,RH and back pressure were set as 75°C,100%and 0.3 MPa.The experimental outcomes of the PEMFC with bio-inspired channels were compared with the experimental results of a conventional triple serpentine flow field.It was observed that among the different flow channel designs considered,the leaf channel design gives the best output in terms of power density.Further,the experimental results of the leaf channel design were compared with those of the interdigitated leaf channel design.The PEMFC with the interdigitated leaf channel design was found to generate 6.72%more power density than the non-interdigitated leaf channel design.The fuel cell with interdigitated leaf channel design generated5.58%more net power density than the fuel cell with non-interdigitated leaf channel design after considering the parasitic losses.展开更多
基金funded by Shanghai Natural Science Foundation(No.12ZR1414700)。
文摘Magnetic field design is essential for the operation of Hall thrusters.This study focuses on utilizing a genetic algorithm to optimize the magnetic field configuration of SPT70.A 2D hybrid PIC-DSMC and channel-wall erosion model are employed to analyze the plume divergence angle and wall erosion rate,while a Farady probe measurement and laser profilometry system are set up to verify the simulation results.The results demonstrate that the genetic algorithm contributes to reducing the divergence angle of the thruster plumes and alleviating the impact of high-energy particles on the discharge channel wall,reducing the erosion by 5.5%and 2.7%,respectively.Further analysis indicates that the change from a divergent magnetic field to a convergent magnetic field,combined with the upstream shift of the ionization region,contributes to the improving the operation of the Hall thruster.
基金supported by a grant from National Key R&D Plan of China(Grant No.2023YFB2504503).
文摘To advance the performance of solid oxide fuel cells(SOFCs),this work proposes a novel biomimetic flow field architecture inspired by the geometric arrangement of sunflower florets.Drawing on natural principles of optimal spatial distribution,a multi-physics simulation model of the resulting Sunflower Bionic Flow Field(SBFF)was developed.Building upon this foundation,an enhanced configuration was introduced by integrating an annular channel,yielding a modified variant referred to as Modified Sunflower Bionic Flow Field(MSBFF).For comparative purposes,a conventional Traditional Parallel Flow Field(TPFF)was also analyzed under identical conditions.Simulation results underscore the superior gas distribution performance of the bionic configurations.Both SBFF and MSBFF significantly improved the homogeneity of reactant gas molar concentration throughout the flow domain.Relative to the TPFF,the SBFF achieved a 13.32%increase in current density,while the MSBFF reached an enhancement of 15.09%.Correspondingly,peak power densities rose by 14.07%and 16.55%,respectively.Furthermore,these bio-inspired structures contributed to improved thermal regulation,as evidenced by a reduction in average electrolyte temperature by 3.22%for the SBFF and 2.92%for the MSBFF.To further optimize performance,the influence of Fibonacci spiral channel count within the MSBFF design was systematically investigated.Results reveal a strong positive correlation between the number of spiral channels and electrochemical output.In particular,the MSBFF with 16 spiral channels(MSBFF-16)demonstrated the most favorable electrical and thermal characteristics.At an operating voltage of 0.7 V,MSBFF-16 exhibited a current density increase of 1.27%and 0.94%over MSBFF and MSBFF-12,respectively.Likewise,peak power density improved by 2.69%and 1.67%.Finally,the study examined the impact of varying inlet mass fractions of oxygen and hydrogen on SOFC performance.Distinct trends were observed:increasing the oxygen mass fraction markedly enhanced heat transfer and current density,while greater hydrogen mass fractions significantly boosted fuel utilization.These findings highlight the crucial role of reactant composition and flow field topology in governing the electrochemical and thermal efficiency of SOFC systems.
文摘The shape optimization is studied by adopting the domain integrated method which is based on the calculus of variations during the shape design sensitivity analysis. A new method of improving the efficiency of the design velocity field analysis and the quality of the finite element method (FEM) mesh is put forward. The sensitivity analysis which is based on the calculus of variations is used in the shape optimization. The design velocity field is solved by Herrmann method. An example shows that both the quality of the FEM mesh and the efficiency of the computing of the design velocity field are improved by Herrmann method. So the effect and the efficiency of the shape optimization are guaranteed. If using sensitivity analysis which is based on the calculus of variations in the shape optimization, the sensitivity analysis can be a relatively independent module. The efficiency of computing the design velocity field and the quality of mesh will be improved by using Herrmann method.
基金financial support from the National Key R&D Program of China(No.2022YFE0204100)the National Natural Science Foundation of China(Nos.U23B20152 and 52402479)。
文摘Hall thrusters with large height-radius ratio,owing to their unique advantages in compactness,lightweight,and high performance,have progressively emerged as a preferred choice for diverse space propulsion applications in the future.However,the amplification of the annular effect in structures with a large height-radius ratio poses a practical problem of plume over-focusing,which seriously restricts the further improvement of Hall thruster performance and the extension of its life.In this study,the formation mechanism of over-focused plume is deeply investigated,and it is ascertained that an intensified radial electric field directed towards the inner wall within the channel serves as a key contributing factor.This phenomenon is fundamentally attributed to structural characteristics of large height-radius ratio that induce pronounced inward inclination of field lines within strong magnetic field zone.Based on this,the design concept of focused magnetic field is proposed,wherein straight magnetic field lines are established within the strong magnetic field zone to generate a quasi-axial accelerating electric field.Simultaneously,the symmetrical magnetic field inside the channel ensures ionization concentration near the channel center,thereby achieving optimal matching between the ionization zone and accelerating field.Experimental results demonstrate that employing a focused magnetic field significantly reduces the divergence half-angle of the plume and yields an excellently barrel-shaped focusing plume morphology in HEP-1350PM.Consequently,the total efficiency of the thruster surpasses 60%,while erosion belt on the inner wall is shortened by nearly 50%.These advancements effectively enhance thruster performance and prolong its operational lifespan.This study can not only resolve practical problems associated with plume over-focusing,but also provide a fundamental guiding principle for magnetic field design of Hall thrusters.
文摘This paper presents the preliminary design of poloidal field power supply system of HT-7U super-conducting tokamak. With an emphasis on AC/DC power converter, DC circuit breaker, quench protection, harmonic suppression and static var. compensation, and AC power system, the design principle and features are introduced, the design scheme and R & D progress are described, the simulation studies and laboratory test are presented too.
基金financial support and to the Center for Petroleum Asset Risk Management of the University of Texas at Austin for hospitality and an exciting research environment
文摘Interwell connectivities are fundamental parameters required to manage waterfloods in oil reservoirs. Data-driven models, such as the capacitance-resistance model （CRM）, are fast tools to estimate these parameters from time-correlations of input （injection rates） and output （production rates） signals. Noise and structure of the input time-series impose limits on the information that can be extracted from a given data-set. This work uses the CRM to study general prescriptions for the design of input signals that enhance the information content of injection/production data in the estimation of well-to-well interactions. Numerical schemes and general features of the optimal input signal strategy are derived for this problem.
文摘HT7U is a large fusion experimental device. It will be built in the Institute of Plasma Physics of Chinese Academy of Sciences. The mission of HT-7U is to develop the scientific basis for a continuously operating tokama-k fusion reactor. This paper describes only a toroidal field (TF) superconducting magnet system of HT7U. In this paper, design criteria of conductor and stability analysis, coil winding and support structure design of magnet system, mechanical calculation and stress analysis, heat load evaluation are given.
基金supported by the National Magnetic Confinement Fusion Research Program of China (2011GB106000)
文摘The design of the poloidal field （PF） system includes the ohmic heating field system and the equilibrium （EQ） field system, and is the basis for the design of a magnetic confinement fusion device. A coupling between the poloidal and plasma currents, especially the eddy current in the stabilizing shell, yields design difficulties. The effects of the eddy current in the stabilizing shell on the poloidal magnetic field also cannot be ignored. A new PF system design is thus proposed. By using a low-μ material （μ = 0.001, ε = 1） instead of a conductive shell, an electromagnetic model is established that can provide a continuous eddy current distribution on the conductive shell. In this model, a 3D time-domain problem with shells translates into a 2D magnetostatic problem, and the accuracy of the calculation is improved. Based on these current distributions, we design the PF system and analyze how the EQ coils and conductive shell affect the plasma EQ when the plasma ramps up. To meet the mainframe design requirements and achieve an efficient power-supply design, the position and connection of the poloidal coils are optimized further.
文摘The HT-7U superconducting tokamak is an advanced steady-state plasma physics experimental device to be built in the Institute of Plasma Physics, the Chinese Academy of Sciences (IPP-CAS). The plasma current is 1 MA and the major and minor radius are 1.78 m and 0.4m respectively, with an elongation of 1.85. The preliminary engineering design of the poloidal field (PF) and toroidal field (TF) magnet systems have been done. The PF system is composed of twelve superconducting coils located symmetrically about the equator plane. The central solenoid (CS) assembly is formed by six coils. The TF system consists of 16 superconducting coils. The NbTi cable-in-conduit conductor or (CICC) cooled by a supercritical helium at 4.5 K is chosen as a superconductor for all of the PF and TF coils. At this temperature, the peak magnetic field on the PF magnets is about 4.51 T .The maximum volt-second capacity and the duration of plasma inductive discharge are about 10 Vs and 10 seconds respectively. The stray field in plasma initial region is quite low ( 1.5× 10 -3 T). The magnetic field on the TF magnet is 5.8 T while the toroidal field at the center of the device (R = 1.7 m) is 3.5 T and the ripple of the TF is less than 0.62% at the outer plasma surface (R = 2.1 m). All of the PF and TF magnets are stable during all modes of operation including the plasma disruption. The final design of the PF system is the result of an iterative process involving the use of equilibrium code EQT, magnetic code EFFI, and other codes, which have been developed by our designing group.
文摘Two design axioms and axiomatic approach were discussed. As an example of application, design process of a new style single prop was illustrated in term of axi- oms.
基金Sponsored by the Science and Technology Projects of Heilongjiang Province (Grant No.GB07C20202 and LC06C16)
文摘In the paper the three-dimensional flow fields are numerically simulated in the vertical-shaft mechanical mix tank of a water treatment plant by means of FLUENT software based on the method of Computational Fluid Dynamics (CFD). The influences of design parameters on flow fields and the mixing effect are analyzed. Firstly,the prediction capability of the turbulence model adopted in simulations is evaluated. And then,the mesh independence is checked up. Finally,the flow fields in various dimensionless blade diameters and dimensionless shaft spans are numerically simulated respectively. The results have shown that the numerical simulation method based on CFD is a feasible assistance for the optimal designs of mixers. Moreover,the optimal design of the blade diameter should take into account both the flow field and the power consumption. The optimization of the shaft span is to achieve a relatively even distribution of the flow field without any rupture. With the consideration of an optimal design,the dimensionless blade diameter and dimensionless shaft span should be 0.45 and 0.57 respectively in the case.
文摘This paper presents quiet zone design using ultrasonic transducers for local active control in pure tone diffuse fields. Most of researches in local active noise control used conventional loudspeakers for the secondary sources to produce quiet zones. Recently ultrasonic transducers have been used for the secondary sources to control the plane wave in active noise control. However there is no research related to active noise control in diffuse fields using ultrasonic transducers. Therefore this study uses ultrasonic transducers for the secondary sources to control the diffuse fields. The quiet zone produced using ultrasonic transducers in single tone diffuse fields has been analyzed through simulations in this work. The results showed that quiet zones created using ultrasonic transducers were larger than those created using conventional loudspeakers. This is due to the fact that the audible sound pressure produced by the ultrasonic transducers decays slowly with the distance. Therefore the secondary field created by an ultrasonic transducer could fit the primary field better and the larger zone of quiet could be obtained using the ultrasonic transducer. Also the audible sound produced by the ultrasonic transducers is directional;therefore the sound pressure amplification outside the quiet zones was lower.
文摘Performance of the proton exchange membrane fuel cell(PEMFC)is appreciably affected by the channel geometry.The branching structure of a plant leaf and human lung is an efficient network to distribute the nutrients in the respective systems.The same nutrient transport system can be mimicked in the flow channel design of a PEMFC,to aid even reactant distribution and better water management.In this work,the effect of bio-inspired flow field designs such as lung and leaf channel design bipolar plates,on the performance of a PEMFC was examined experimentally at various operating conditions.A PEMFC of 49 cm2 area,with a Nafion 212 membrane with a 40%catalyst loading of 0.4 mg·cm-2 on the anode side and also 0.6 mg·cm-2 on the cathode side is assembled by incorporating the bio-inspired channel bipolar plate,and was tested on a programmable fuel-cell test station.The impact of the working parameters like reactants’relative humidity(RH),back pressure and fuel cell temperature on the performance of the fuel cell was examined;the operating pressure remains constant at 0.1 MPa.It was observed that the best performance was attained at a back pressure of 0.3 MPa,75°C operating temperature and 100%RH.The three flow channels were also compared at different operating pressures ranging from 0.1 MPa to 0.3 MPa,and the other parameters such as operating temperature,RH and back pressure were set as 75°C,100%and 0.3 MPa.The experimental outcomes of the PEMFC with bio-inspired channels were compared with the experimental results of a conventional triple serpentine flow field.It was observed that among the different flow channel designs considered,the leaf channel design gives the best output in terms of power density.Further,the experimental results of the leaf channel design were compared with those of the interdigitated leaf channel design.The PEMFC with the interdigitated leaf channel design was found to generate 6.72%more power density than the non-interdigitated leaf channel design.The fuel cell with interdigitated leaf channel design generated5.58%more net power density than the fuel cell with non-interdigitated leaf channel design after considering the parasitic losses.
