The microstructure evolution and properties of an Al-Zn-Mg-Cu alloy were investigated under different non-linear cooling processes from the solution temperature, combined with in-situ electrical resistivity measuremen...The microstructure evolution and properties of an Al-Zn-Mg-Cu alloy were investigated under different non-linear cooling processes from the solution temperature, combined with in-situ electrical resistivity measurements, selected area diffraction patterns （SADPs）, transmission electron microscopy （TEM）, and tensile tests. The relative resistivity was calculated to characterize the phase transformation of the experimental alloy during different cooling processes. The results show that at high temperatures, the microstructure evolutions change from the directional diffusion of Zn and Mg atoms to the precipitation of S phase, depending on the cooling rate. At medium temperatures, q phase nucleates on A13Zr dispersoids and grain boundaries under fast cooling conditions, while S phase precipitates under the slow cooling conditions. The strength and ductility of the aged alloy suffer a significant deterioration due to the heterogeneous precipitation in medium temperature range. At low temperatures, homogeneously nucleated GP zone, η′ and η phases precipitate.展开更多
Based on the fluid network theory,the possibility of utilizing regenerator flow resistance to suppress the direct current （DC） flow induced by the introduction of a double-inlet in a pulse tube cooler is investigate...Based on the fluid network theory,the possibility of utilizing regenerator flow resistance to suppress the direct current （DC） flow induced by the introduction of a double-inlet in a pulse tube cooler is investigated theoretically. The calculation results show that increasing regenerator flow resistance can lead to a smaller extent of DC flow.Therefore,a better stability performance of the cooler can be realized.On this basis,the stability characteristics of the cooler with various regenerator matrix arrangements are studied by experiments.By replacing 30% space of 247 screens of stainless steel mesh at the cold part of the regenerator by lead balls of 0.25 mm diameter,a long-time stable temperature output at 80 K region is achieved. This achievement provides a new way to obtain stable performance for pulse tube coolers at high temperature and is helpful for its application.展开更多
With the consideration of the thermal management and heat sink requirements,a cooling device is designed and the thermal resistance of this device is calculated with a single 5 W power LED.The thermal design of a sing...With the consideration of the thermal management and heat sink requirements,a cooling device is designed and the thermal resistance of this device is calculated with a single 5 W power LED.The thermal design of a single 5 W power LED is reasonable,effective and the result has been simulated.This design also instruct other power LEDs' thermal design.Provided is a reliable and effective method for the design of power LED illumination lamps and lanterns.展开更多
This experiment is to study the special resistant induced by the high-speed evaporation surrounding themoving high-temperature particles. An observable equipment was designed, in which the first 11 experiments wereper...This experiment is to study the special resistant induced by the high-speed evaporation surrounding themoving high-temperature particles. An observable equipment was designed, in which the first 11 experiments wereperformed by pouring one or several Zirconia spheres with various high-temperature and a diameter of 3～ 10 mminto a water pool. The particles falling-down speeds were recorded by high-speed photographic instrumentation,and pressures and water temperatures were measured. A comparison between the experiments with cold and hotspheres respectively, employing three different sphere types each, was presented. The experimental data, com-pared with the theory of the evaporation drag model, are nearly identical.展开更多
Temperature gradient and cooling rate have an obvious effect on formation of methane hydrate. The process for formation of methane hydrate in coarse sand is monitored to tmderstand the relationship between temperature...Temperature gradient and cooling rate have an obvious effect on formation of methane hydrate. The process for formation of methane hydrate in coarse sand is monitored to tmderstand the relationship between temperature gradient and cooling rate and nucleation, growth and distribution of methane hydrate by using the electrical resistivity method. The results show that the change of resistivity can better reflect the nucleation and growth and distribution of methane hydrate. Temperature gradient promotes the nucleation, formation, and formation rate of methane hydrate. At a temperature gradient of 0.11℃/cm, the rate of methane hydrate formation and saturation reaches a maximum. Cooling rate has little effect on the methane hydrate formation process. Judging from the outcome of final spatial distribution of methane hydrate, the cooling rate has an obvious but irregular effect in coarse sand. The effect of tempera^re gradient on distribution of methane hydrate in coarse sand is less than that of cooling rate. At a temperature gradient of 0.07℃/cm, methane hydrate is distributed uniformly in the sample. If the temperature gradient is higher or lower than this value, the hydrate is enriched in the upper layer of sample.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
Thickness of falling water film out of tubes is one of critical factors of heat transfer of evaporative air cooler. A new method of resistance measurement was developed to measure thickness of the film. When the resis...Thickness of falling water film out of tubes is one of critical factors of heat transfer of evaporative air cooler. A new method of resistance measurement was developed to measure thickness of the film. When the resistance probe on the tip of micrometer touches the surface and bottom of the film, two corresponding sudden reductions of resistance occurs, and the difference of two graduations on the micrometer displays the thickness of the film. The film thickness of eleven angles was measured in five kinds of water flows and results varies from 0.8933mm to 1.7233 mm. Mean thickness and mean heat transfer coefficient of the film out of the tube was calculated.展开更多
The boiling heat transfer of evaporation cooling in a billet reheating furnace was simulated.The results indicate that the bubbles easily aggregate inside of the elbow and upper side of the horizontal regions in theπ...The boiling heat transfer of evaporation cooling in a billet reheating furnace was simulated.The results indicate that the bubbles easily aggregate inside of the elbow and upper side of the horizontal regions in theπshaped support tubes.The circulation velocity increasing helps to improve the uniformity of vapor distribution and decrease the difference of vapor volume fraction between upper and down at end of the horizontal sections.With the increase of circulation velocity,the resistance loss and the circulation ratio both increase,but the former will decrease with the increase of work pressure.展开更多
Cold-test experiment of an S-band broadband high power coupled-cavity traveling-wave tube(CCTWT)is introduced in this paper.The dispersion characteristic,the synchronous voltage and the interaction impedance of this S...Cold-test experiment of an S-band broadband high power coupled-cavity traveling-wave tube(CCTWT)is introduced in this paper.The dispersion characteristic,the synchronous voltage and the interaction impedance of this S-band CCTWT are measured.The experimental results are in agreement with the numerical simulation values.展开更多
Flooding phenomenon limits the stability and the flow of a liquid film falling along the walls of a channel in which a gas is flowing upwards. As known, the entrainment effect can completely prevent the liquid to fall...Flooding phenomenon limits the stability and the flow of a liquid film falling along the walls of a channel in which a gas is flowing upwards. As known, the entrainment effect can completely prevent the liquid to fall from its natural flow. The present work proposes a new mechanistic model for the prediction of the onset of flooding in vertical and inclined pipes in the presence of obstructions, as well as taking into account the viscosity effect. The good performance of the model in the different geometrical conditions and for variable viscosities of the liquid component assesses the validity of the hypothesis that the instability of a wavelike disturbance limits the countercurrent flow in a channel.展开更多
Solar sail is used to achieve a geocentric sun-synchronous frozen orbit.This kind of orbit combines the characteristics of both sun-synchronous orbits and frozen orbits.Furthermore,the impossible orbits for a typical ...Solar sail is used to achieve a geocentric sun-synchronous frozen orbit.This kind of orbit combines the characteristics of both sun-synchronous orbits and frozen orbits.Furthermore,the impossible orbits for a typical spacecraft such as sun-synchronous orbits whose inclination is less than 90° are also possible for solar sail.To achieve a sun-synchronous frozen orbit,the characteristic acceleration of the sail is chosen properly.In addition,the attitude of the sail is adjusted to keep the sun-synchronous and frozen characteristics.The perturbations including atmosphere drag,third-body gravitational forces and shaded regions are discussed,where the atmosphere drag is cancelled by solar radiation pressure force,third-body gravitational forces have negligible effects on the orbit and the shaded region can be avoided by choosing the classical orbit elements of the sail.At last,a numerical example is employed to validate the sun-synchronous frozen characteristics of the sail.展开更多
Experimental study and one dimensional model analysis were conducted to investigate cooling performance of an integrated impingement and pin fin cooling device. A typical configuration specimen was made and tested in ...Experimental study and one dimensional model analysis were conducted to investigate cooling performance of an integrated impingement and pin fin cooling device. A typical configuration specimen was made and tested in a large scale low speed closed-looped wind tunnel. Detailed two-dimensional contour maps of the temperature and cooling effectiveness were obtained for different pressure ratios and therefore different coolant flow-rates through the tested specimen. The experimental results showed that very high cooling effectiveness can be achieved by this cooling device with relatively small amount of coolant flow. Based on the theory of transpiration cooling in porous material, a one dimensional heat transfer model was established to analyze the effect of various parameters on cooling effectiveness. It was found from this model that the variation of heat transfer on the gas side, including heat transfer coefficient and film cooling effectiveness, of the specimen created much more effect on its cooling effectiveness than that of the coolant side. The predictions of the one-dimensional mode were compared and agreed well with the experimental data.展开更多
Local structure of cooling panel has great effects on the heat transfer in the cooling channel for the scramjet. The problems of flow dead area and mass flow rate non-uniform distribution caused by the local structure...Local structure of cooling panel has great effects on the heat transfer in the cooling channel for the scramjet. The problems of flow dead area and mass flow rate non-uniform distribution caused by the local structure effect the cooling effectiveness in the channel seriously. Numerical simulation to the flow field of scramjet cold panel with four different fuel injection island structures respectively has been carried out using the CFD commercial software-CFX in this research. The results reveal that flow dead area has been eliminated and flow field has been improved for the optimized structure. Furthermore, local resistance loss has been decreased and the mass flow rate non-uniform distribution in the channel has been reduced. Based on the optimized results, some suggestions about the local design of cooling panel have been proposed in this research.展开更多
基金Project(2014GK2013)supported by the Science and Technology Program of Hunan Province,China
文摘The microstructure evolution and properties of an Al-Zn-Mg-Cu alloy were investigated under different non-linear cooling processes from the solution temperature, combined with in-situ electrical resistivity measurements, selected area diffraction patterns （SADPs）, transmission electron microscopy （TEM）, and tensile tests. The relative resistivity was calculated to characterize the phase transformation of the experimental alloy during different cooling processes. The results show that at high temperatures, the microstructure evolutions change from the directional diffusion of Zn and Mg atoms to the precipitation of S phase, depending on the cooling rate. At medium temperatures, q phase nucleates on A13Zr dispersoids and grain boundaries under fast cooling conditions, while S phase precipitates under the slow cooling conditions. The strength and ductility of the aged alloy suffer a significant deterioration due to the heterogeneous precipitation in medium temperature range. At low temperatures, homogeneously nucleated GP zone, η′ and η phases precipitate.
基金The National Natural Science Foundation of China(No.50406009).
文摘Based on the fluid network theory,the possibility of utilizing regenerator flow resistance to suppress the direct current （DC） flow induced by the introduction of a double-inlet in a pulse tube cooler is investigated theoretically. The calculation results show that increasing regenerator flow resistance can lead to a smaller extent of DC flow.Therefore,a better stability performance of the cooler can be realized.On this basis,the stability characteristics of the cooler with various regenerator matrix arrangements are studied by experiments.By replacing 30% space of 247 screens of stainless steel mesh at the cold part of the regenerator by lead balls of 0.25 mm diameter,a long-time stable temperature output at 80 K region is achieved. This achievement provides a new way to obtain stable performance for pulse tube coolers at high temperature and is helpful for its application.
文摘With the consideration of the thermal management and heat sink requirements,a cooling device is designed and the thermal resistance of this device is calculated with a single 5 W power LED.The thermal design of a single 5 W power LED is reasonable,effective and the result has been simulated.This design also instruct other power LEDs' thermal design.Provided is a reliable and effective method for the design of power LED illumination lamps and lanterns.
文摘This experiment is to study the special resistant induced by the high-speed evaporation surrounding themoving high-temperature particles. An observable equipment was designed, in which the first 11 experiments wereperformed by pouring one or several Zirconia spheres with various high-temperature and a diameter of 3～ 10 mminto a water pool. The particles falling-down speeds were recorded by high-speed photographic instrumentation,and pressures and water temperatures were measured. A comparison between the experiments with cold and hotspheres respectively, employing three different sphere types each, was presented. The experimental data, com-pared with the theory of the evaporation drag model, are nearly identical.
基金supported by the Chinese Academy of Sciences Action-plan for Western Project(No.KZCX2-XB3-03)the National Natural Science Foundation of China(No.41001038,51266005)the National Natural Science Foundation of China(No.41101070,1106ZBB007)
文摘Temperature gradient and cooling rate have an obvious effect on formation of methane hydrate. The process for formation of methane hydrate in coarse sand is monitored to tmderstand the relationship between temperature gradient and cooling rate and nucleation, growth and distribution of methane hydrate by using the electrical resistivity method. The results show that the change of resistivity can better reflect the nucleation and growth and distribution of methane hydrate. Temperature gradient promotes the nucleation, formation, and formation rate of methane hydrate. At a temperature gradient of 0.11℃/cm, the rate of methane hydrate formation and saturation reaches a maximum. Cooling rate has little effect on the methane hydrate formation process. Judging from the outcome of final spatial distribution of methane hydrate, the cooling rate has an obvious but irregular effect in coarse sand. The effect of tempera^re gradient on distribution of methane hydrate in coarse sand is less than that of cooling rate. At a temperature gradient of 0.07℃/cm, methane hydrate is distributed uniformly in the sample. If the temperature gradient is higher or lower than this value, the hydrate is enriched in the upper layer of sample.
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Acknowledgments： The study is one of branches of a key project of Chinese National Programs for Foundation Research and Development, thanks for the supporting from the National Nature Science Foundation. The new method to measure thickness of wager film has applied an utility model patent in China （No. 200620098211.4）.
文摘Thickness of falling water film out of tubes is one of critical factors of heat transfer of evaporative air cooler. A new method of resistance measurement was developed to measure thickness of the film. When the resistance probe on the tip of micrometer touches the surface and bottom of the film, two corresponding sudden reductions of resistance occurs, and the difference of two graduations on the micrometer displays the thickness of the film. The film thickness of eleven angles was measured in five kinds of water flows and results varies from 0.8933mm to 1.7233 mm. Mean thickness and mean heat transfer coefficient of the film out of the tube was calculated.
基金Project(51171041) supported by the National Natural Science Foundation of China
文摘The boiling heat transfer of evaporation cooling in a billet reheating furnace was simulated.The results indicate that the bubbles easily aggregate inside of the elbow and upper side of the horizontal regions in theπshaped support tubes.The circulation velocity increasing helps to improve the uniformity of vapor distribution and decrease the difference of vapor volume fraction between upper and down at end of the horizontal sections.With the increase of circulation velocity,the resistance loss and the circulation ratio both increase,but the former will decrease with the increase of work pressure.
文摘Cold-test experiment of an S-band broadband high power coupled-cavity traveling-wave tube(CCTWT)is introduced in this paper.The dispersion characteristic,the synchronous voltage and the interaction impedance of this S-band CCTWT are measured.The experimental results are in agreement with the numerical simulation values.
文摘Flooding phenomenon limits the stability and the flow of a liquid film falling along the walls of a channel in which a gas is flowing upwards. As known, the entrainment effect can completely prevent the liquid to fall from its natural flow. The present work proposes a new mechanistic model for the prediction of the onset of flooding in vertical and inclined pipes in the presence of obstructions, as well as taking into account the viscosity effect. The good performance of the model in the different geometrical conditions and for variable viscosities of the liquid component assesses the validity of the hypothesis that the instability of a wavelike disturbance limits the countercurrent flow in a channel.
基金supported by the National Natural Science Foundation of China (Grants Nos.10902056 and 10832004)State Key Lab of Astronautical Dynamics of China (Grant No. 2011ADL-DW0201)
文摘Solar sail is used to achieve a geocentric sun-synchronous frozen orbit.This kind of orbit combines the characteristics of both sun-synchronous orbits and frozen orbits.Furthermore,the impossible orbits for a typical spacecraft such as sun-synchronous orbits whose inclination is less than 90° are also possible for solar sail.To achieve a sun-synchronous frozen orbit,the characteristic acceleration of the sail is chosen properly.In addition,the attitude of the sail is adjusted to keep the sun-synchronous and frozen characteristics.The perturbations including atmosphere drag,third-body gravitational forces and shaded regions are discussed,where the atmosphere drag is cancelled by solar radiation pressure force,third-body gravitational forces have negligible effects on the orbit and the shaded region can be avoided by choosing the classical orbit elements of the sail.At last,a numerical example is employed to validate the sun-synchronous frozen characteristics of the sail.
文摘Experimental study and one dimensional model analysis were conducted to investigate cooling performance of an integrated impingement and pin fin cooling device. A typical configuration specimen was made and tested in a large scale low speed closed-looped wind tunnel. Detailed two-dimensional contour maps of the temperature and cooling effectiveness were obtained for different pressure ratios and therefore different coolant flow-rates through the tested specimen. The experimental results showed that very high cooling effectiveness can be achieved by this cooling device with relatively small amount of coolant flow. Based on the theory of transpiration cooling in porous material, a one dimensional heat transfer model was established to analyze the effect of various parameters on cooling effectiveness. It was found from this model that the variation of heat transfer on the gas side, including heat transfer coefficient and film cooling effectiveness, of the specimen created much more effect on its cooling effectiveness than that of the coolant side. The predictions of the one-dimensional mode were compared and agreed well with the experimental data.
文摘Local structure of cooling panel has great effects on the heat transfer in the cooling channel for the scramjet. The problems of flow dead area and mass flow rate non-uniform distribution caused by the local structure effect the cooling effectiveness in the channel seriously. Numerical simulation to the flow field of scramjet cold panel with four different fuel injection island structures respectively has been carried out using the CFD commercial software-CFX in this research. The results reveal that flow dead area has been eliminated and flow field has been improved for the optimized structure. Furthermore, local resistance loss has been decreased and the mass flow rate non-uniform distribution in the channel has been reduced. Based on the optimized results, some suggestions about the local design of cooling panel have been proposed in this research.
