EAST （Experimental Advanced Superconducting Tokamak） is a tokamak with su- perconducting toroidal and poloidal magnets operated at 4.5 K. In order to reduce the thermal load applied on the surfaces of all cryogenica...EAST （Experimental Advanced Superconducting Tokamak） is a tokamak with su- perconducting toroidal and poloidal magnets operated at 4.5 K. In order to reduce the thermal load applied on the surfaces of all cryogenically cooled components and keep the heat load of the cryogenic system at a minimum, a continuous radiation shield system located between the magnet system and warm components is adopted. The main loads to which the thermal shield system is subjected are gravity, seismic, electromagnetic and thermal gradients. This study employed NASTRAN and ANSYS finite element codes to analyze the stress under a spectrum of loading conditions and combinations, providing a theoretical basis for an optimization design of the structure.展开更多
The ITER equatorial thermal shield is located inside the cryostat and outside the vacuum vessel, and its purpose is to provide a thermal shield from hot components to the superconducting magnets. Electromagnetic analy...The ITER equatorial thermal shield is located inside the cryostat and outside the vacuum vessel, and its purpose is to provide a thermal shield from hot components to the superconducting magnets. Electromagnetic analysis of the equatorial thermal shield was performed using the ANSYS code, because electromagnetic load was one of the main loads. The 40 sector finite element model was established including the vacuum vessel, equatorial thermal shield, and superconducting magnets. The main purpose of this analysis was to investigate the eddy current and electromagnetic force in the equatorial thermal shield during plasma disruption. Stress analysis was implemented under the electromagnetic load. The results show that the equatorial thermal shield can accommodate the calculated electromagnetic loads.展开更多
Thermal analysis of the equatorial thermal shield for ITER is conducted in order to confirm that the cooling tube design was reasonable under both the plasma operational and the baking operational conditions. The stru...Thermal analysis of the equatorial thermal shield for ITER is conducted in order to confirm that the cooling tube design was reasonable under both the plasma operational and the baking operational conditions. The structural performance was analyzed by means of the finite element software ANSYS. A comparison of the results with design requirements shows that the results of the simulation are within allowable design requirements, which indicates the feasibility and reliability of the equatorial thermal shield structure.展开更多
Boron carbide/natural rubber latex(B_4 C/NRL)flexible films were prepared via dip-molding with B_4 C content in the range of 5–55 wt% for thermal neutron(0.0253 e V) shielding. B_4 C was well dispersed in NRL accordi...Boron carbide/natural rubber latex(B_4 C/NRL)flexible films were prepared via dip-molding with B_4 C content in the range of 5–55 wt% for thermal neutron(0.0253 e V) shielding. B_4 C was well dispersed in NRL according to microscopic observation. Both the inside and outside surfaces of the film were smooth. For B_4 C/NRL flexible films, the minimum elongation at break was greater than 600%, the minimum tensile strength was greater than 12 MPa, and the hardness was in the range of 35–55 HA,which were suitable for preparing flexible wearable products. The attenuation efficiencies of the B_4 C/NRL flexible films for thermal neutrons were also calculated. The B_4 C/NRL flexible films exhibit good attenuation effect for thermal neutrons.展开更多
With continuous enhancement of gas-turbine inlet temperature and rapid increase of radiant heat transfer,thermal barrier coating(TBC)materials with a combination of low thermal conductivity and good high-temperature t...With continuous enhancement of gas-turbine inlet temperature and rapid increase of radiant heat transfer,thermal barrier coating(TBC)materials with a combination of low thermal conductivity and good high-temperature thermal radiation shielding performance play vital roles in ensuring the durability of metallic blades.However,yttria-stabilized zirconia(YSZ),as the state-of-the-art TBC and current industry standard,is unable to meet such demands since it is almost translucent to high-temperature thermal radiation.Besides,poor corrosion resistance of YSZ to molten calcia-magnesia-alumina-silicates(CMAS)also impedes its application in sand,dust,or volcanic ash laden environments.In order to improve the hightemperature thermal radiation shielding performance and CMAS resistance of YSZ and further reduce its thermal conductivity,two medium-entropy(ME)oxide ceramics,ME(Y,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)and ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2),were designed and prepared by pressureless sintering of binary powder compacts in this work.ME(Y,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)presents cubic structure but a trace amount of secondary phase,while ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)displays a combination of tetragonal phase(81.6 wt.%)and cubic phase(18.4 wt.%).Both ME(Y,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)and ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)possess better high-temperature thermal radiation shielding performance than YSZ.Especially,the high-temperature thermal radiation shielding performance of ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)is superior to that of ME(Y,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)due to its narrower band gap and correspondingly higher infrared absorbance(above 0.7)at the waveband of 1 to 5μm.The two ME oxides also display significantly lower thermal conductivity than YSZ and close thermal expansion coefficients(TECs)to YSZ and Ni-based superalloys.In addition,the two ME oxides possess excellent CMAS resistance.After attack by molten CMAS at 1250℃for 4 h,merely~2μm thick penetration layer has been formed and the structure below the penetration layer is still intact.These results demonstrate that ME(Me,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)(Me=Y and Ta),especially ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2),are promising thermal barrier materials for high-temperature thermal radiation shielding and CMAS blocking.展开更多
In this article, hybrid fillers with different dimensions, namely, 2-dimensional（2-D） expanded graphite（EG） and 1-dimensional（1-D） multi-walled carbon nanotubes（CNTs）, were added to aromatic nylon MXD6 matrix ...In this article, hybrid fillers with different dimensions, namely, 2-dimensional（2-D） expanded graphite（EG） and 1-dimensional（1-D） multi-walled carbon nanotubes（CNTs）, were added to aromatic nylon MXD6 matrix via melt-blending, to enhance its thermal and electrical conductivity as well as electromagnetic interference shielding effectiveness（EMI SE）. For ternary composites of MXD6/EG/CNTs, the electrical conductivity reaches up nine orders of magnitude higher compared to that of the neat MXD6 sample, which turned the polymer-based composites from an insulator to a conductor, and the thermal conductivity has been enhanced by 477% compared with that of neat MXD6 sample. Meanwhile, the EMI SE of ternary composite reaches ~50 d B at the overall filler loading of only 18 wt%. This work can provide guidance for the preparation of polymer composites with excellent thermal and electrical conductivity via using hybrid filler.展开更多
Superheater tubes temperature control is a necessity for long lifetime, high efficiency and high load following capability in boiler. This study reports a new approach for the control strategy design of boilers with s...Superheater tubes temperature control is a necessity for long lifetime, high efficiency and high load following capability in boiler. This study reports a new approach for the control strategy design of boilers with special shields. The presented control strategy is developed based on radiation thermal shields with low emissivity coefficient and high reflectivity or scattering coefficient. In order to simulate the combustion event in boiler and heat transfer to superheater tubes, an effective set of computational fluid dynamic (CFD) codes is used. Results indicate a successful identification of over- heated zones on platen superheater tubes and effect of radiation shields for solving this problem.展开更多
ITER blanket design has progressed significantly since 2001, which resulted in a reduction in cost and an increase in performance with respect to FDR 2001. One of the most important improvements is the new coolant flo...ITER blanket design has progressed significantly since 2001, which resulted in a reduction in cost and an increase in performance with respect to FDR 2001. One of the most important improvements is the new coolant flow configuration in the shield block （ SB ） . In the current design TM, the cooling circuit in the SB is a matrix of radial holes which are arranged in eight poloidal rows. The rows are fed in parallel by front headers and back drilled collectors, and merge in four couples through the front header. These four couples of rows are linked in series by transverse holes. In the current design, a special shape of flow driver is mounted inside the radial hole, and coolant flows through clearance between the driver and drilled radial hole, which allows achieving a high coolant velocity,展开更多
In this work, the polyacrylonitrile containing gadolinium nanofibers for thermal neutron protection were successfully fabricated by electrospunning and followed by in situ self-polymerization. Scanning electron micros...In this work, the polyacrylonitrile containing gadolinium nanofibers for thermal neutron protection were successfully fabricated by electrospunning and followed by in situ self-polymerization. Scanning electron microscopy(SEM) and energy-dispersive spectroscopy(EDS) results show that there are no beads on the smooth surface of the nanofibers and gadolinium elements are uniformly dispersed in the matrix. The thermal analysis and FTIR results prove that gadolinium methacrylate is induced in situ selfpolymerization during the heat treatment. The leaching rate of Gd^(3+) decreases from 79.97% to 10.74% tested by lowfield nuclear magnetic resonance(LF-NMR) method after the self-polymerization of gadolinium methacrylate in the matrix when the nanofibers were immersed in water for7 days. The thermal neutron shielding analysis calculated by MCNP program shows that above 99% thermal neutrons are absorbed when traveling through the 2-mm-thick polyacrylonitrile containing gadolinium nanofibers.展开更多
Further development of the photovoltaic industry is restricted by the productivity of mono-crystalline silicon technology due to its requirements of low cost and high efficient photocells. The heat shield is not only ...Further development of the photovoltaic industry is restricted by the productivity of mono-crystalline silicon technology due to its requirements of low cost and high efficient photocells. The heat shield is not only the important part of the thermal field in Czochralski（Cz） mono-crystalline silicon furnace, but also one of the most important factors influencing the silicon crystal growth. Large-diameter Cz-Si crystal growth process is taken as the study object, Based on FEM numerical simulation, different heat shield structures are analyzed to investigate the heater power, the melt-crystal interface shape, the argon flow field, and the oxygen concentration at the melt-crystal interface in the process of large Cz-Si crystal growth. The impact of these factors on the growth efficiency and crystal quality are analyzed. The results show that the oxygen concentration on the melt-crystal interface and the power consumption of the heater stay high due to the lack of a heat shield in the crystal growth system. Argon circumfluence is generated on the external side of the right angle heat shield. By the right-angle heat shield, the speed of gas flow is lowered on the melt free surface, and the temperature gradient of the free surface is increased around the melt-crystal interface. It is not conducive for the stable growth of crystal. The shape of the melt-crystal interface and the argon circulation above the melt free surface are improved by the inclined heat shield. Compared with the others, the system pulling rate is increased and the lowest oxygen concentration is achieved at the melt-crystal interface with the composite heat shield. By the adoption of the optimized composite heat shield in experiment, the real melt-crystal interface shapes and its deformation laws obtained by Quick Pull Separation Method at different pulling rates agree with the simulation results. The results show that the method of simulation is feasible. The proposed research provides the theoretical foundation for the thermal field design of the large diameter Cz-Si monocrystalline growth.展开更多
The aim of this study was to synthesize and evaluate the thermal properties and ultraviolet(UV)resistance of zinc oxide-functionalized halloysite nanotubes(HNT–ZnO).The HNT–ZnO was synthesized using a facile solvent...The aim of this study was to synthesize and evaluate the thermal properties and ultraviolet(UV)resistance of zinc oxide-functionalized halloysite nanotubes(HNT–ZnO).The HNT–ZnO was synthesized using a facile solvent-free route.The properties of the HNT–ZnO nanofillers were characterized using zeta-potential measurement,X-ray diffraction(XRD),field-emission scanning electron microscopy(FESEM),transmission electron microscopy(TEM),Fourier transform infrared spectroscopy(FTIR),and thermogravimetric analysis(TGA).The immobilization of ZnO nanoparticles onto HNT is feasible even at the lowest mass ratio of HNT/ZnO.The TGA results indicate that the thermal stability of the HNT–ZnO nanofillers is higher than that of the HNT.Furthermore,UV?Vis diffuse reflectance spectroscopy(UV-DRS)results show that the HNT–ZnO achieve a total reflectance as high as approximately 87.5%in the UV region,as compare with 66.9%for the HNT.In summary,the immobilization of ZnO onto HNT is a viable approach for increasing the thermal stability and improving the UV shielding of HNT.展开更多
A novel thermal-protective coating has been successfully prepared by CPED process on a cast Al-12%Si alloy with the addition of ZrO2 nano-particles in the electrolyte. The microstructures and phase composition of the ...A novel thermal-protective coating has been successfully prepared by CPED process on a cast Al-12%Si alloy with the addition of ZrO2 nano-particles in the electrolyte. The microstructures and phase composition of the coatings were analyzed by SEM and XRD, and the heat insulation performance and the thermal shock resistance of the coatings were investigated. With ZrO2 nanoparticles addition, the cathode plasma discharge on the coating surface is more obvious than that without ZrO2 nanoparticles addition, the coating is more uniform and compact, and the thickness of the coating increases. Furthermore, the content of Zr and Y elements increases and the degree of crystallization of the coating is more complete. The formation of the solid solution of yttrium stabilized zirconia is promoted by cathode plasma discharge. In addition, the thermal insulation temperature increases as ZrO2 nano-particles are added to the electrolyte. After 1 000 cycles of thermal shock, there was no cracking in the coating surface layer, which indicated that the CPED coating with ZrO2 nanoparticles addition possessed a good thermal shock resistance.展开更多
A spacecraft designed to operate in a planetary atmosphere must have an adequate heat shield to withstand the high heat fluxes and heat loads that are generated by aerodynamic heating. Very often, the mass of the ther...A spacecraft designed to operate in a planetary atmosphere must have an adequate heat shield to withstand the high heat fluxes and heat loads that are generated by aerodynamic heating. Very often, the mass of the thermal protection system is a significant fraction of the total mass of the vehicle. In contrast, performing maneuvers in the atmosphere, that would be very costly in terms of propellant consumption if they were performed completely outside of the atmosphere in a classic way, is a very attractive prospective technique. The advantages and disadvantages in terms of total mass spared must be determined. The mission investigated involves an aeroassisted coplanar transfer from a high to a low Earth orbit. The approach uses a combination of three propulsive impulses in space together with an aerodynamic maneuver in the atmosphere. The heat shield adopted is fully ablative, given the expected high values of the entering heat flux. The convenience of the aeroassisted maneuver and the influence of the parameters involved are evaluated in comparison to a conventional Hohmann transfer. In particular, a parametric analysis is performed by varying the following characteristics of the vehicle: aerodynamic efficiency, mass-to-surface ratio, deorbit impulse, and initial altitude of the orbit. The influence of the thermal protection system is examined by assessing the impact of the type of ablative material employed, the thermal safety factor, and the allowable temperature for the adhesive layer on the substructure. The analysis is conducted with a highly representative thermal model by coupling the dynamic and thermal analyses and using a genetic optimizer. The optimization methodology and the thermal model are completely original. The results indicate the importance of choosing low-density ablative materials, of adopting a suitable thermal safety factor, and of choosing high-performance adhesives. The optimal trajectories obtained correspond to a zero second propulsive impulse.展开更多
A new composite of silicone rubber and boric acid was developed to be used as a personal wearing for protection from nuclear radiation. The capability of this material for absorbing thermal neutrons of different inten...A new composite of silicone rubber and boric acid was developed to be used as a personal wearing for protection from nuclear radiation. The capability of this material for absorbing thermal neutrons of different intensities followed by a detonation of nuclear weapon has been investigated. This investigation was performed by using californium-252 neutron source of like fission spectrum. The thermal neutron flux was measured behind different thicknesses of the developed material using a BF3 detector. Two positions of measurements were performed;at position near the detonation where the intensity of thermal neutron flux is low and at position far from the detonation where the intensity of thermal neutron is high. For both cases, the contribution of total thermal, initial incident and new produced thermal neutron fluxes are measured. The obtained results indicated that, addition of boron with concentration of about 17% to the silicon rubber tends to decrease the flux by more than 70%.展开更多
ITER in-wall shielding （IIS） is situated between the doubled shells of the ITER Vacuum Vessel （IVV）. Its main functions are applied in shielding neutron, gamma-ray and toroidal field ripple reduction. The structur...ITER in-wall shielding （IIS） is situated between the doubled shells of the ITER Vacuum Vessel （IVV）. Its main functions are applied in shielding neutron, gamma-ray and toroidal field ripple reduction. The structure of IIS has been modelled according to the IVV design criteria which has been updated by the ITER team （IT）. Static analysis and thermal expansion analysis were performed for the structure. Thermal-hydraulic analysis verified the heat removal capability and resulting temperature, pressure, and velocity changes in the coolant flow. Consequently, our design work is possibly suitable as a reference for IT＇s updated or final design in its next step.展开更多
文摘EAST （Experimental Advanced Superconducting Tokamak） is a tokamak with su- perconducting toroidal and poloidal magnets operated at 4.5 K. In order to reduce the thermal load applied on the surfaces of all cryogenically cooled components and keep the heat load of the cryogenic system at a minimum, a continuous radiation shield system located between the magnet system and warm components is adopted. The main loads to which the thermal shield system is subjected are gravity, seismic, electromagnetic and thermal gradients. This study employed NASTRAN and ANSYS finite element codes to analyze the stress under a spectrum of loading conditions and combinations, providing a theoretical basis for an optimization design of the structure.
基金supported by the International Thermonuclear Experimental Reactor (ITER) Specific Plan of China(No.2009GB101004)
文摘The ITER equatorial thermal shield is located inside the cryostat and outside the vacuum vessel, and its purpose is to provide a thermal shield from hot components to the superconducting magnets. Electromagnetic analysis of the equatorial thermal shield was performed using the ANSYS code, because electromagnetic load was one of the main loads. The 40 sector finite element model was established including the vacuum vessel, equatorial thermal shield, and superconducting magnets. The main purpose of this analysis was to investigate the eddy current and electromagnetic force in the equatorial thermal shield during plasma disruption. Stress analysis was implemented under the electromagnetic load. The results show that the equatorial thermal shield can accommodate the calculated electromagnetic loads.
基金supported by International Thermonuclear Experimental Reactor(ITER)Specific Plan(2009GB101004)
文摘Thermal analysis of the equatorial thermal shield for ITER is conducted in order to confirm that the cooling tube design was reasonable under both the plasma operational and the baking operational conditions. The structural performance was analyzed by means of the finite element software ANSYS. A comparison of the results with design requirements shows that the results of the simulation are within allowable design requirements, which indicates the feasibility and reliability of the equatorial thermal shield structure.
基金supported by the National Natural Science Foundation of China(No.11405149)the Sichuan Academic and Technical Leader Program(No.DTR201501)
文摘Boron carbide/natural rubber latex(B_4 C/NRL)flexible films were prepared via dip-molding with B_4 C content in the range of 5–55 wt% for thermal neutron(0.0253 e V) shielding. B_4 C was well dispersed in NRL according to microscopic observation. Both the inside and outside surfaces of the film were smooth. For B_4 C/NRL flexible films, the minimum elongation at break was greater than 600%, the minimum tensile strength was greater than 12 MPa, and the hardness was in the range of 35–55 HA,which were suitable for preparing flexible wearable products. The attenuation efficiencies of the B_4 C/NRL flexible films for thermal neutrons were also calculated. The B_4 C/NRL flexible films exhibit good attenuation effect for thermal neutrons.
基金financially supported by the National Natural Science Foundation of China(No.51772275 and No.51972089)Distinguished Young Foundation of Henan Province(No.202300410355)。
文摘With continuous enhancement of gas-turbine inlet temperature and rapid increase of radiant heat transfer,thermal barrier coating(TBC)materials with a combination of low thermal conductivity and good high-temperature thermal radiation shielding performance play vital roles in ensuring the durability of metallic blades.However,yttria-stabilized zirconia(YSZ),as the state-of-the-art TBC and current industry standard,is unable to meet such demands since it is almost translucent to high-temperature thermal radiation.Besides,poor corrosion resistance of YSZ to molten calcia-magnesia-alumina-silicates(CMAS)also impedes its application in sand,dust,or volcanic ash laden environments.In order to improve the hightemperature thermal radiation shielding performance and CMAS resistance of YSZ and further reduce its thermal conductivity,two medium-entropy(ME)oxide ceramics,ME(Y,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)and ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2),were designed and prepared by pressureless sintering of binary powder compacts in this work.ME(Y,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)presents cubic structure but a trace amount of secondary phase,while ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)displays a combination of tetragonal phase(81.6 wt.%)and cubic phase(18.4 wt.%).Both ME(Y,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)and ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)possess better high-temperature thermal radiation shielding performance than YSZ.Especially,the high-temperature thermal radiation shielding performance of ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)is superior to that of ME(Y,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)due to its narrower band gap and correspondingly higher infrared absorbance(above 0.7)at the waveband of 1 to 5μm.The two ME oxides also display significantly lower thermal conductivity than YSZ and close thermal expansion coefficients(TECs)to YSZ and Ni-based superalloys.In addition,the two ME oxides possess excellent CMAS resistance.After attack by molten CMAS at 1250℃for 4 h,merely~2μm thick penetration layer has been formed and the structure below the penetration layer is still intact.These results demonstrate that ME(Me,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)(Me=Y and Ta),especially ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2),are promising thermal barrier materials for high-temperature thermal radiation shielding and CMAS blocking.
基金financially supported by the National Natural Science Foundation of China(Nos.21274095 and 51573102)
文摘In this article, hybrid fillers with different dimensions, namely, 2-dimensional（2-D） expanded graphite（EG） and 1-dimensional（1-D） multi-walled carbon nanotubes（CNTs）, were added to aromatic nylon MXD6 matrix via melt-blending, to enhance its thermal and electrical conductivity as well as electromagnetic interference shielding effectiveness（EMI SE）. For ternary composites of MXD6/EG/CNTs, the electrical conductivity reaches up nine orders of magnitude higher compared to that of the neat MXD6 sample, which turned the polymer-based composites from an insulator to a conductor, and the thermal conductivity has been enhanced by 477% compared with that of neat MXD6 sample. Meanwhile, the EMI SE of ternary composite reaches ~50 d B at the overall filler loading of only 18 wt%. This work can provide guidance for the preparation of polymer composites with excellent thermal and electrical conductivity via using hybrid filler.
文摘Superheater tubes temperature control is a necessity for long lifetime, high efficiency and high load following capability in boiler. This study reports a new approach for the control strategy design of boilers with special shields. The presented control strategy is developed based on radiation thermal shields with low emissivity coefficient and high reflectivity or scattering coefficient. In order to simulate the combustion event in boiler and heat transfer to superheater tubes, an effective set of computational fluid dynamic (CFD) codes is used. Results indicate a successful identification of over- heated zones on platen superheater tubes and effect of radiation shields for solving this problem.
文摘ITER blanket design has progressed significantly since 2001, which resulted in a reduction in cost and an increase in performance with respect to FDR 2001. One of the most important improvements is the new coolant flow configuration in the shield block （ SB ） . In the current design TM, the cooling circuit in the SB is a matrix of radial holes which are arranged in eight poloidal rows. The rows are fed in parallel by front headers and back drilled collectors, and merge in four couples through the front header. These four couples of rows are linked in series by transverse holes. In the current design, a special shape of flow driver is mounted inside the radial hole, and coolant flows through clearance between the driver and drilled radial hole, which allows achieving a high coolant velocity,
基金financially supported by Postgraduate Research & Practice Innovation Program of Jiangsu Province (No. KYLX_1337)the Excellent Doctorial Dissertations Fund of Yangzhou University
文摘In this work, the polyacrylonitrile containing gadolinium nanofibers for thermal neutron protection were successfully fabricated by electrospunning and followed by in situ self-polymerization. Scanning electron microscopy(SEM) and energy-dispersive spectroscopy(EDS) results show that there are no beads on the smooth surface of the nanofibers and gadolinium elements are uniformly dispersed in the matrix. The thermal analysis and FTIR results prove that gadolinium methacrylate is induced in situ selfpolymerization during the heat treatment. The leaching rate of Gd^(3+) decreases from 79.97% to 10.74% tested by lowfield nuclear magnetic resonance(LF-NMR) method after the self-polymerization of gadolinium methacrylate in the matrix when the nanofibers were immersed in water for7 days. The thermal neutron shielding analysis calculated by MCNP program shows that above 99% thermal neutrons are absorbed when traveling through the 2-mm-thick polyacrylonitrile containing gadolinium nanofibers.
基金Supported by National Natural Science Foundation of China(Grant Nos.61075044,F0304)
文摘Further development of the photovoltaic industry is restricted by the productivity of mono-crystalline silicon technology due to its requirements of low cost and high efficient photocells. The heat shield is not only the important part of the thermal field in Czochralski（Cz） mono-crystalline silicon furnace, but also one of the most important factors influencing the silicon crystal growth. Large-diameter Cz-Si crystal growth process is taken as the study object, Based on FEM numerical simulation, different heat shield structures are analyzed to investigate the heater power, the melt-crystal interface shape, the argon flow field, and the oxygen concentration at the melt-crystal interface in the process of large Cz-Si crystal growth. The impact of these factors on the growth efficiency and crystal quality are analyzed. The results show that the oxygen concentration on the melt-crystal interface and the power consumption of the heater stay high due to the lack of a heat shield in the crystal growth system. Argon circumfluence is generated on the external side of the right angle heat shield. By the right-angle heat shield, the speed of gas flow is lowered on the melt free surface, and the temperature gradient of the free surface is increased around the melt-crystal interface. It is not conducive for the stable growth of crystal. The shape of the melt-crystal interface and the argon circulation above the melt free surface are improved by the inclined heat shield. Compared with the others, the system pulling rate is increased and the lowest oxygen concentration is achieved at the melt-crystal interface with the composite heat shield. By the adoption of the optimized composite heat shield in experiment, the real melt-crystal interface shapes and its deformation laws obtained by Quick Pull Separation Method at different pulling rates agree with the simulation results. The results show that the method of simulation is feasible. The proposed research provides the theoretical foundation for the thermal field design of the large diameter Cz-Si monocrystalline growth.
基金Universiti Sains Malaysia for Bridging Fund(grant No.304.PBAHAN.6316090)
文摘The aim of this study was to synthesize and evaluate the thermal properties and ultraviolet(UV)resistance of zinc oxide-functionalized halloysite nanotubes(HNT–ZnO).The HNT–ZnO was synthesized using a facile solvent-free route.The properties of the HNT–ZnO nanofillers were characterized using zeta-potential measurement,X-ray diffraction(XRD),field-emission scanning electron microscopy(FESEM),transmission electron microscopy(TEM),Fourier transform infrared spectroscopy(FTIR),and thermogravimetric analysis(TGA).The immobilization of ZnO nanoparticles onto HNT is feasible even at the lowest mass ratio of HNT/ZnO.The TGA results indicate that the thermal stability of the HNT–ZnO nanofillers is higher than that of the HNT.Furthermore,UV?Vis diffuse reflectance spectroscopy(UV-DRS)results show that the HNT–ZnO achieve a total reflectance as high as approximately 87.5%in the UV region,as compare with 66.9%for the HNT.In summary,the immobilization of ZnO onto HNT is a viable approach for increasing the thermal stability and improving the UV shielding of HNT.
基金Funded by the Youth Innovation Team of Shaanxi Universities,Shaanxi Key Research and Development Program(No.2018GY-111)Shaanxi Provincial Department of Education Industrialization Cultivation Project(No.17JF009)Yulin Science and Technology Project(Nos.2016-16-4 and 2018-2-30)
文摘A novel thermal-protective coating has been successfully prepared by CPED process on a cast Al-12%Si alloy with the addition of ZrO2 nano-particles in the electrolyte. The microstructures and phase composition of the coatings were analyzed by SEM and XRD, and the heat insulation performance and the thermal shock resistance of the coatings were investigated. With ZrO2 nanoparticles addition, the cathode plasma discharge on the coating surface is more obvious than that without ZrO2 nanoparticles addition, the coating is more uniform and compact, and the thickness of the coating increases. Furthermore, the content of Zr and Y elements increases and the degree of crystallization of the coating is more complete. The formation of the solid solution of yttrium stabilized zirconia is promoted by cathode plasma discharge. In addition, the thermal insulation temperature increases as ZrO2 nano-particles are added to the electrolyte. After 1 000 cycles of thermal shock, there was no cracking in the coating surface layer, which indicated that the CPED coating with ZrO2 nanoparticles addition possessed a good thermal shock resistance.
文摘A spacecraft designed to operate in a planetary atmosphere must have an adequate heat shield to withstand the high heat fluxes and heat loads that are generated by aerodynamic heating. Very often, the mass of the thermal protection system is a significant fraction of the total mass of the vehicle. In contrast, performing maneuvers in the atmosphere, that would be very costly in terms of propellant consumption if they were performed completely outside of the atmosphere in a classic way, is a very attractive prospective technique. The advantages and disadvantages in terms of total mass spared must be determined. The mission investigated involves an aeroassisted coplanar transfer from a high to a low Earth orbit. The approach uses a combination of three propulsive impulses in space together with an aerodynamic maneuver in the atmosphere. The heat shield adopted is fully ablative, given the expected high values of the entering heat flux. The convenience of the aeroassisted maneuver and the influence of the parameters involved are evaluated in comparison to a conventional Hohmann transfer. In particular, a parametric analysis is performed by varying the following characteristics of the vehicle: aerodynamic efficiency, mass-to-surface ratio, deorbit impulse, and initial altitude of the orbit. The influence of the thermal protection system is examined by assessing the impact of the type of ablative material employed, the thermal safety factor, and the allowable temperature for the adhesive layer on the substructure. The analysis is conducted with a highly representative thermal model by coupling the dynamic and thermal analyses and using a genetic optimizer. The optimization methodology and the thermal model are completely original. The results indicate the importance of choosing low-density ablative materials, of adopting a suitable thermal safety factor, and of choosing high-performance adhesives. The optimal trajectories obtained correspond to a zero second propulsive impulse.
文摘A new composite of silicone rubber and boric acid was developed to be used as a personal wearing for protection from nuclear radiation. The capability of this material for absorbing thermal neutrons of different intensities followed by a detonation of nuclear weapon has been investigated. This investigation was performed by using californium-252 neutron source of like fission spectrum. The thermal neutron flux was measured behind different thicknesses of the developed material using a BF3 detector. Two positions of measurements were performed;at position near the detonation where the intensity of thermal neutron flux is low and at position far from the detonation where the intensity of thermal neutron is high. For both cases, the contribution of total thermal, initial incident and new produced thermal neutron fluxes are measured. The obtained results indicated that, addition of boron with concentration of about 17% to the silicon rubber tends to decrease the flux by more than 70%.
基金the National 973 program of China(No.2004CB720704)
文摘ITER in-wall shielding （IIS） is situated between the doubled shells of the ITER Vacuum Vessel （IVV）. Its main functions are applied in shielding neutron, gamma-ray and toroidal field ripple reduction. The structure of IIS has been modelled according to the IVV design criteria which has been updated by the ITER team （IT）. Static analysis and thermal expansion analysis were performed for the structure. Thermal-hydraulic analysis verified the heat removal capability and resulting temperature, pressure, and velocity changes in the coolant flow. Consequently, our design work is possibly suitable as a reference for IT＇s updated or final design in its next step.
