When the high-pressure gas is exhausted to the vacuum chamber from the nozzle,the underexpanded supersonic jet contained with the Mach disk is generally formed.The eventual purpose of this study is to clarify the unst...When the high-pressure gas is exhausted to the vacuum chamber from the nozzle,the underexpanded supersonic jet contained with the Mach disk is generally formed.The eventual purpose of this study is to clarify the unsteady phenomenon of the underexpanded free jet when the back pressure continuously changes with time.The characteristic of the Mach disk has been clarified in consideration of the diameter and position of it by the numerical analysis in this paper.The sonic jet of the exit Mach number Me=1 is assumed and the axisymmetric conservational equation is solved by the TVD method in the numerical calculation.The diameter and position of the Mach disk differs with the results of a steady jet and the influence on the continuously changing of the back pressure is evidenced from the comparison with the case of steady supersonic jet.展开更多
The pinning of quantized magnetic vortices in superconducting YBa_(2)Cu_(3)O_(7-δ)(YBCO or Y123)thin films with Y_(2)BaCuO_(5)(Y211)nanoinclusions have been investigated over wide temperature range(4.2-77 K).The conc...The pinning of quantized magnetic vortices in superconducting YBa_(2)Cu_(3)O_(7-δ)(YBCO or Y123)thin films with Y_(2)BaCuO_(5)(Y211)nanoinclusions have been investigated over wide temperature range(4.2-77 K).The concentration of Y211 nanoinclusions has been systematically varied inside YBCO thin films prepared by laser ablation technique using surface modified target approach.Large pinning force density values(Fp∼0.5 TNm^(−3)at 4.2 K,9 T)have been observed for the YBCO film with moderate concentration of Y211 nanoinclusions(3.6 area%on ablation target).In addition,uniform enhancement in critical current density(J_(c))was observed in the angular dependent J_(c)measurement of YBCO+Y211 nanocomposite films.Y211 nanoinclusions have been found to be very efficient in pinning the quantized vortices thereby enhancing the in‐field J_(c)values over a wide range of temperature.Increasing the concentration of Y211 secondary phase into Y123 film matrix results into agglomeration of Y211 phase and observed as increased Y211 nanoparticle size.These larger secondary phase nanoparticles are not as efficient pinning centers at lower temperatures as they are at higher temperatures due to substantial reduction of the coherence length at lower temperatures.Investigation of the temperature dependence of J_(c)for YBCO+Y211 nanocomposite films has been conducted and possible vortex pinning mechanism in these nanocomposite films has been discussed.展开更多
Polymer carbon nitride(PCN)is widely used in photocatalysis.However,pristine PCN has disadvantages such as insufficient visible light absorption and low photogenerated carrier separation efficiency that greatly limite...Polymer carbon nitride(PCN)is widely used in photocatalysis.However,pristine PCN has disadvantages such as insufficient visible light absorption and low photogenerated carrier separation efficiency that greatly limited the photocatalytic efficiency.As a non-toxic metal,gallium has the potential to solve the defects of PCN.Gallium ions coordinated with nitrogen in carbon nitride to form Ga-N active sites and improved the photocatalytic activity.The doped potassium ions form a transmission channel for charge redistribution and transfer between adjacent layers,which is beneficial for better separation of photoexcited carriers.In this study,a series of PCN co-doped with gallium and potassium(Ga-K-PCN)were prepared.The experimental results indicated photocatalytic generation of hydrogen peroxide proceeds through the 2e−oxygen reduction reaction pathway.Notably,Nyquist plots and photocurrent results further proved that the presence of Ga-N sites and potassium ion doping could significantly improve the separation/transfer of intra-planar and interlayer charge carriers and thus enhance photocatalytic efficiency.The Ga10-K3-PCN photocatalysts promoted yield of H_(2)O_(2),with reactivity at 28.2μmol/(g·h)and solar-to-chemical conversion efficiency at 0.64%,surpassed that of a typical photo-catalyst based on PCN(0.18%).展开更多
When the high-pressure gas is exhausted to the vacuum chamber from the supersonic nozzle, the overexpanded supersonic jet is formed at specific condition. In two-dimensional supersonic jet, furthermore, it is known th...When the high-pressure gas is exhausted to the vacuum chamber from the supersonic nozzle, the overexpanded supersonic jet is formed at specific condition. In two-dimensional supersonic jet, furthermore, it is known that the hysteresis phenomena for the reflection type of shock wave in the flow field is occurred under the quasi-steady flow and for instance, the transitional pressure ratio between the regular reflection （RR） and Mach reflection （MR） is affected by this phenomenon. Many papers have described the hysteresis phenomena for underexpanded supersonic jet, but this phenomenon under the overexpanded axisymmetric jet has not been detailed in the past papers. The purpose of this study is to clear the hysteresis phenomena for the reflection type of shock wave at the overexpanded axisymmetric jet using the TVD method and to discuss the characteristic of hysteresis phenomena.展开更多
When the shock wave propagating in the straight circular tube reaches at the open end, the impulsive wave is generated by the emission of a shock wave from an open end, and unsteady pulse jet is formed near the open e...When the shock wave propagating in the straight circular tube reaches at the open end, the impulsive wave is generated by the emission of a shock wave from an open end, and unsteady pulse jet is formed near the open end behind the impulsive wave under the specific condition. The pulse jet transits to spherical shock wave with the increase in the strength of shock wave. The strength is dependent on the Mach number of shock wave, which attenuates by propagation distance from the open end. In this study, the mechanism of generating the unsteady pulse jet, the characteristics of the pressure distribution in the flow field and the emission of shock wave from straight circular tube which has the infinite flange at open end are analyzed numerically by the TVD method. Strength of spherical shock wave, relation of shock wave Mach number,distance decay of spherical shock wave and directional characteristics are clarified.展开更多
Aluminum is an abundant metal in the earth’s crust that turns out to be toxic in acidic environments.Many plants are affected by the presence of aluminum at the whole plant level,at the organ level,and at the cellula...Aluminum is an abundant metal in the earth’s crust that turns out to be toxic in acidic environments.Many plants are affected by the presence of aluminum at the whole plant level,at the organ level,and at the cellular level.Tobacco as a cash crop(Nicotiana tabacum L.)is a widely cultivated plant worldwide and is also a good model organism for research.Although there are many articles on Al-phytotoxicity in the literature,reviews on a single species that are economically and scientifically important are limited.In this article,we not only provide the biology associated with tobacco Al-toxicity,but also some essential information regarding the effects of this metal on other plant species(even animals).This review provides information on aluminum localization and uptake process by different staining techniques,as well as the effects of its toxicity at different compartment levels and the physiological consequences derived from them.In addition,molecular studies in recent years have reported specific responses to Al toxicity,such as overexpression of various protective proteins.Besides,this review discusses data on various organelle-based responses,cell death,and other mechanisms,data on tobacco plants and other kingdoms relevant to these studies.展开更多
Ageing behaviors of the positive electrode of lithium ion battery are characterized by measuring mechanical properties of the electrode reeds, such as resonance frequency and internal friction, as a function of temper...Ageing behaviors of the positive electrode of lithium ion battery are characterized by measuring mechanical properties of the electrode reeds, such as resonance frequency and internal friction, as a function of temperature. In the measurements of the electrode reeds with a sandwich structure of active material film and current collector of Al foil, two thermally-activated relaxation processes can be observed on the polyvinylidene difluoride binder in the active material film. Namely, a surface-related relaxation at ~150 K and a relaxation corresponding to the β-phase transition at ~240 K in the polymer binder can be observed at high signal/noise ratio. The resonance frequency decreases and the internal friction increases after charge/discharge cycling. The changes in activation energies of the relaxation processes also indicate that the measurement of mechanical properties of the positive electrode is an effective method for characterizing ageing behaviors of the positive electrode as a whole.展开更多
The numerical analysis of a turbulent sonic jet from a two-dimensional convergent nozzle has been carried out using the compressible k-? turbulence model and TVD finite difference scheme. Numerical conditions have bee...The numerical analysis of a turbulent sonic jet from a two-dimensional convergent nozzle has been carried out using the compressible k-? turbulence model and TVD finite difference scheme. Numerical conditions have been varied over a range of operating pressure ratios from 1.893 to 6.0 which cover the jet flow conditions from correctly expanded to underexpanded. Numerical flow visualization of sonic jet structure using the computer schlieren, a relation between shock cell length in the jet with the operating pressure ratio and the pressure distribution along jet centerline are obtained. Also, a transition process of a two-dimensional sonic jet from correctly expanded to underexpanded conditions is shown in detail and a flow model of jet structure is proposed.展开更多
The effect of nozzle geometry on sonic line and characteristics of supersonic air jet was studied. Computational fluid dynamics was applied in this study. The axisymmetric nozzle geometries investigated were two diffe...The effect of nozzle geometry on sonic line and characteristics of supersonic air jet was studied. Computational fluid dynamics was applied in this study. The axisymmetric nozzle geometries investigated were two different contour converging nozzles, two different conically converging sharp-edged nozzles and a sharp-edged orifice. The results show that the supersonic jet structure, sonic line and streamlines in supersonic jet are strongly influenced by the nozzle geometry, and the total pressure loss increases with the increase of Mach disk diameter. The present numerical simulation is an effective tool to evaluate compressible flows in supersonic air jet.展开更多
When the underexpanded supersonic jet impinges on the obstacle, it is well known that the self-induced flow oscillation occurs at the specific condition of the pressure ratio in the flowfield, the position of an obsta...When the underexpanded supersonic jet impinges on the obstacle, it is well known that the self-induced flow oscillation occurs at the specific condition of the pressure ratio in the flowfield, the position of an obstacle and so on. This oscillation is related with the noise problems of aeronautical and other industrial engineering so that the characteristic and the mechanism of self-induced flow oscillation have to be cleared to control the various noise problems. But, it seems that the characteristics of the oscillated flowfield and the mechanism of oscillation have to be more clear to control the oscillation. This paper aims to clarify the effect of the plate position and the width for the self-induced flow oscillation of an underexpanded supersonic jet impinging on the perpendicular plate by the experiment and the numerical analysis. From the results, it is clear that the occurring domain of the self-induced flow oscillation and its dimension strongly depend on the plate position and the width.展开更多
An air classifier is used in the recycling process of covered electric wire in the recycling factories, in which the covered electric wires are crushed, sieved, and classified by the air classifier, which generates wa...An air classifier is used in the recycling process of covered electric wire in the recycling factories, in which the covered electric wires are crushed, sieved, and classified by the air classifier, which generates wastes. In these factories, operators manually adjust the air flow rate while checking the wastes discharged from the separator outlet. However, the adjustments are basically done by trial and error, and it is difficult to do them appropriately. In this study, we tried to develop the image processing system that calculates the ratio of copper (Cu) product and polyvinyl chloride (PVC) in the wastes as a substitute for the operator’s eyes. Six colors of PVC (white, gray, green, blue, black, and red) were used in the present work. An image consists of foreground and background. An image’s regions of interest are objects (Cu particles) in its foreground. However, the particles having a color similar to the background color are buried in the background. Using the difference of two color backgrounds, we separated particles and background without dependent of background. The Otsu’ thresholding was employed to choose the threshold to maximize the degree of separation of the particles and background. The ratio of Cu to PVC pixels from mixed image was calculated by linear discriminant analysis. The error of PVC pixels resulted in zero, whereas the error of Cu pixels arose to 4.19%. Comparing the numbers of Cu and PVC pixels within the contour, the minority of the object were corrected to the majority of the object. The error of Cu pixels discriminated as PVC incorrectly became zero percent through this correction.展开更多
When a gas expands through a convergent nozzle in which the ratio of the ambient to the stagnation pressures is higher than that of the critical one, the issuing jet from the nozzle is under-expanded. If a flat plate ...When a gas expands through a convergent nozzle in which the ratio of the ambient to the stagnation pressures is higher than that of the critical one, the issuing jet from the nozzle is under-expanded. If a flat plate is placed normal to the jet at a certain distance from the nozzle, a detached shock wave is formed at a region between the nozzle exit and the plate. In general, supersonic moist air jet technologies with non-equilibrium condensation are very often applied to industrial manufacturing processes. In spite of the importance in major characteristics of the supersonic moist air jets impinging to a solid body, its qualitative characteristics are not known satisfactorily. In the present study, the effect of the non-equilibrium condensation on the under-expanded air jet impinging on a vertical flat plate is investigated numerically in the case with non-equilibrium condensation, frequency of oscillation for the flow field becomes larger than that without the non-equilibrium condensation, and amplitudes of static pressure become small compared with those of dry air. Furthermore, the numerical results are compared with experimental ones.展开更多
When a Pressure wave propagates along a constant area straight tube and reaches at the open end, an impulsive wave is emitted outward from the tube exit toward the surrounding area and causes an impulsive noise like a...When a Pressure wave propagates along a constant area straight tube and reaches at the open end, an impulsive wave is emitted outward from the tube exit toward the surrounding area and causes an impulsive noise like a sonic boom. In order to clarify the magnitude of an impulsive wave obtained by the discharge of a weak shock wave born an open end of a tube in relation to the noise problem and the industrial devices, the experimental and numerical investigations have been carried out for various strength of a shock wave. A simple open end shock tube with the flange at the tube exit.was used and the numerical calculation using the TVD scheme was performed. The effective equations which concerns with the magnitude of an impulsive wave generated by the emission of a shock wave have been obtained from the procedure of the open end correction based on the aeroacoustic theory and the numerical results. The influence of open end correction length and the diameter of a flange on the magnitude of an impulsive wave has been discussed.展开更多
In the present study,a computational fluid dynamics work was performed to investigate the occurrence of the shock wave by condensation in supersonic moist air jet.The unsteady,compressible axisymmetric Navier-Stokes e...In the present study,a computational fluid dynamics work was performed to investigate the occurrence of the shock wave by condensation in supersonic moist air jet.The unsteady,compressible axisymmetric Navier-Stokes equation is solved by TVD(Total Variation Diminishing) scheme in this study.The numerical simulations have been performed for low pressure ratio and various humidities.The results show the occurrence of the shock wave in supersonic moist air jet for a low pressure ratio when Mach disk does not occur,depending on humidity of the air.展开更多
In the present study, a computational fluid dynamics method has been applied to investigate the effects of initial degree of supersaturation at reservoir condition on under-expanded sonic jet structures, such as Mach ...In the present study, a computational fluid dynamics method has been applied to investigate the effects of initial degree of supersaturation at reservoir condition on under-expanded sonic jet structures, such as Mach disk location and diameter, barrel shock wave and jet boundary. The axisymmetric nozzle geometry investigated was a converging nozzle with straight part. As a result, it was found that the overpressures due to condensation generate and the characteristics of flow with generation of overpressure due to condensation in the jet were different from those without condensation.展开更多
Electrical and structural properties of nanocrystalline solids of C80 fullerene encapsulated with a Lu3N cluster, Lu3N@C80, have been studied by measuring x-ray photoemission spectra, x-ray diffraction, and current-vo...Electrical and structural properties of nanocrystalline solids of C80 fullerene encapsulated with a Lu3N cluster, Lu3N@C80, have been studied by measuring x-ray photoemission spectra, x-ray diffraction, and current-voltage characteristics of the Lu3N@C80/Au Schottky contact in the temperature range of 300 - 500 K. The nanocrystalline solid sample of Lu3N@C80 fullerene consists of grains characterized with an fcc structure and those grains become larger in size after pressing the powder sample at 1.25 GPa. The current-voltage characteristics measured at various temperatures showed that there are no significant dependences on both the Schottky barrier and the carrier mobility on electric field. The Schottky barrier of the Lu3N@C80/Au contact is determined to be 0.71 ± 0.04 eV.展开更多
When the underexpanded supersonic jet impinges on the obstacle, it is well known that the self-induced flow os- cillation occurs. This oscillation depends on the pressure ratio in the flowfield, the position of an obs...When the underexpanded supersonic jet impinges on the obstacle, it is well known that the self-induced flow os- cillation occurs. This oscillation depends on the pressure ratio in the flowfield, the position of an obstacle and is related with the noise problems of aeronautical and other industrial engineering. The characteristic and the mechanism of self-induced flow oscillation, have to be clarified to control various noise problems. But, it seems that the characteristics of the oscillated flowfield and the mechanism of an oscillation have to be more cleared to control the oscillation. This paper aims to clarify the effect of the pressure ratio and the obstacle position and the mechanism of self-induced flow oscillation by numerical analysis and experiment, when the underexpanded su- personic jet impinges on the cylindrical body. From the result of this study, it is clear that occurrence of the self-induced flow osciUation depends on the pressure balance in the flowfield.展开更多
文摘When the high-pressure gas is exhausted to the vacuum chamber from the nozzle,the underexpanded supersonic jet contained with the Mach disk is generally formed.The eventual purpose of this study is to clarify the unsteady phenomenon of the underexpanded free jet when the back pressure continuously changes with time.The characteristic of the Mach disk has been clarified in consideration of the diameter and position of it by the numerical analysis in this paper.The sonic jet of the exit Mach number Me=1 is assumed and the axisymmetric conservational equation is solved by the TVD method in the numerical calculation.The diameter and position of the Mach disk differs with the results of a steady jet and the influence on the continuously changing of the back pressure is evidenced from the comparison with the case of steady supersonic jet.
基金supported by the ALCA project of Japan Science and Technology Agency.
文摘The pinning of quantized magnetic vortices in superconducting YBa_(2)Cu_(3)O_(7-δ)(YBCO or Y123)thin films with Y_(2)BaCuO_(5)(Y211)nanoinclusions have been investigated over wide temperature range(4.2-77 K).The concentration of Y211 nanoinclusions has been systematically varied inside YBCO thin films prepared by laser ablation technique using surface modified target approach.Large pinning force density values(Fp∼0.5 TNm^(−3)at 4.2 K,9 T)have been observed for the YBCO film with moderate concentration of Y211 nanoinclusions(3.6 area%on ablation target).In addition,uniform enhancement in critical current density(J_(c))was observed in the angular dependent J_(c)measurement of YBCO+Y211 nanocomposite films.Y211 nanoinclusions have been found to be very efficient in pinning the quantized vortices thereby enhancing the in‐field J_(c)values over a wide range of temperature.Increasing the concentration of Y211 secondary phase into Y123 film matrix results into agglomeration of Y211 phase and observed as increased Y211 nanoparticle size.These larger secondary phase nanoparticles are not as efficient pinning centers at lower temperatures as they are at higher temperatures due to substantial reduction of the coherence length at lower temperatures.Investigation of the temperature dependence of J_(c)for YBCO+Y211 nanocomposite films has been conducted and possible vortex pinning mechanism in these nanocomposite films has been discussed.
基金The support of Mitsubishi Chemical Corporation and the Japan Society for the Promotion of Science Grant-in-Aid for Scientific Research B(No.20H02847)the Support for Pioneering Research Initiated by the Next Generation program for Japan Science and Technology Agency(No.JPMJSP2154)the National Natural Science Foundation of China(No.52103008)are greatly acknowledged.
文摘Polymer carbon nitride(PCN)is widely used in photocatalysis.However,pristine PCN has disadvantages such as insufficient visible light absorption and low photogenerated carrier separation efficiency that greatly limited the photocatalytic efficiency.As a non-toxic metal,gallium has the potential to solve the defects of PCN.Gallium ions coordinated with nitrogen in carbon nitride to form Ga-N active sites and improved the photocatalytic activity.The doped potassium ions form a transmission channel for charge redistribution and transfer between adjacent layers,which is beneficial for better separation of photoexcited carriers.In this study,a series of PCN co-doped with gallium and potassium(Ga-K-PCN)were prepared.The experimental results indicated photocatalytic generation of hydrogen peroxide proceeds through the 2e−oxygen reduction reaction pathway.Notably,Nyquist plots and photocurrent results further proved that the presence of Ga-N sites and potassium ion doping could significantly improve the separation/transfer of intra-planar and interlayer charge carriers and thus enhance photocatalytic efficiency.The Ga10-K3-PCN photocatalysts promoted yield of H_(2)O_(2),with reactivity at 28.2μmol/(g·h)and solar-to-chemical conversion efficiency at 0.64%,surpassed that of a typical photo-catalyst based on PCN(0.18%).
文摘When the high-pressure gas is exhausted to the vacuum chamber from the supersonic nozzle, the overexpanded supersonic jet is formed at specific condition. In two-dimensional supersonic jet, furthermore, it is known that the hysteresis phenomena for the reflection type of shock wave in the flow field is occurred under the quasi-steady flow and for instance, the transitional pressure ratio between the regular reflection （RR） and Mach reflection （MR） is affected by this phenomenon. Many papers have described the hysteresis phenomena for underexpanded supersonic jet, but this phenomenon under the overexpanded axisymmetric jet has not been detailed in the past papers. The purpose of this study is to clear the hysteresis phenomena for the reflection type of shock wave at the overexpanded axisymmetric jet using the TVD method and to discuss the characteristic of hysteresis phenomena.
文摘When the shock wave propagating in the straight circular tube reaches at the open end, the impulsive wave is generated by the emission of a shock wave from an open end, and unsteady pulse jet is formed near the open end behind the impulsive wave under the specific condition. The pulse jet transits to spherical shock wave with the increase in the strength of shock wave. The strength is dependent on the Mach number of shock wave, which attenuates by propagation distance from the open end. In this study, the mechanism of generating the unsteady pulse jet, the characteristics of the pressure distribution in the flow field and the emission of shock wave from straight circular tube which has the infinite flange at open end are analyzed numerically by the TVD method. Strength of spherical shock wave, relation of shock wave Mach number,distance decay of spherical shock wave and directional characteristics are clarified.
文摘Aluminum is an abundant metal in the earth’s crust that turns out to be toxic in acidic environments.Many plants are affected by the presence of aluminum at the whole plant level,at the organ level,and at the cellular level.Tobacco as a cash crop(Nicotiana tabacum L.)is a widely cultivated plant worldwide and is also a good model organism for research.Although there are many articles on Al-phytotoxicity in the literature,reviews on a single species that are economically and scientifically important are limited.In this article,we not only provide the biology associated with tobacco Al-toxicity,but also some essential information regarding the effects of this metal on other plant species(even animals).This review provides information on aluminum localization and uptake process by different staining techniques,as well as the effects of its toxicity at different compartment levels and the physiological consequences derived from them.In addition,molecular studies in recent years have reported specific responses to Al toxicity,such as overexpression of various protective proteins.Besides,this review discusses data on various organelle-based responses,cell death,and other mechanisms,data on tobacco plants and other kingdoms relevant to these studies.
文摘Ageing behaviors of the positive electrode of lithium ion battery are characterized by measuring mechanical properties of the electrode reeds, such as resonance frequency and internal friction, as a function of temperature. In the measurements of the electrode reeds with a sandwich structure of active material film and current collector of Al foil, two thermally-activated relaxation processes can be observed on the polyvinylidene difluoride binder in the active material film. Namely, a surface-related relaxation at ~150 K and a relaxation corresponding to the β-phase transition at ~240 K in the polymer binder can be observed at high signal/noise ratio. The resonance frequency decreases and the internal friction increases after charge/discharge cycling. The changes in activation energies of the relaxation processes also indicate that the measurement of mechanical properties of the positive electrode is an effective method for characterizing ageing behaviors of the positive electrode as a whole.
文摘The numerical analysis of a turbulent sonic jet from a two-dimensional convergent nozzle has been carried out using the compressible k-? turbulence model and TVD finite difference scheme. Numerical conditions have been varied over a range of operating pressure ratios from 1.893 to 6.0 which cover the jet flow conditions from correctly expanded to underexpanded. Numerical flow visualization of sonic jet structure using the computer schlieren, a relation between shock cell length in the jet with the operating pressure ratio and the pressure distribution along jet centerline are obtained. Also, a transition process of a two-dimensional sonic jet from correctly expanded to underexpanded conditions is shown in detail and a flow model of jet structure is proposed.
文摘The effect of nozzle geometry on sonic line and characteristics of supersonic air jet was studied. Computational fluid dynamics was applied in this study. The axisymmetric nozzle geometries investigated were two different contour converging nozzles, two different conically converging sharp-edged nozzles and a sharp-edged orifice. The results show that the supersonic jet structure, sonic line and streamlines in supersonic jet are strongly influenced by the nozzle geometry, and the total pressure loss increases with the increase of Mach disk diameter. The present numerical simulation is an effective tool to evaluate compressible flows in supersonic air jet.
文摘When the underexpanded supersonic jet impinges on the obstacle, it is well known that the self-induced flow oscillation occurs at the specific condition of the pressure ratio in the flowfield, the position of an obstacle and so on. This oscillation is related with the noise problems of aeronautical and other industrial engineering so that the characteristic and the mechanism of self-induced flow oscillation have to be cleared to control the various noise problems. But, it seems that the characteristics of the oscillated flowfield and the mechanism of oscillation have to be more clear to control the oscillation. This paper aims to clarify the effect of the plate position and the width for the self-induced flow oscillation of an underexpanded supersonic jet impinging on the perpendicular plate by the experiment and the numerical analysis. From the results, it is clear that the occurring domain of the self-induced flow oscillation and its dimension strongly depend on the plate position and the width.
文摘An air classifier is used in the recycling process of covered electric wire in the recycling factories, in which the covered electric wires are crushed, sieved, and classified by the air classifier, which generates wastes. In these factories, operators manually adjust the air flow rate while checking the wastes discharged from the separator outlet. However, the adjustments are basically done by trial and error, and it is difficult to do them appropriately. In this study, we tried to develop the image processing system that calculates the ratio of copper (Cu) product and polyvinyl chloride (PVC) in the wastes as a substitute for the operator’s eyes. Six colors of PVC (white, gray, green, blue, black, and red) were used in the present work. An image consists of foreground and background. An image’s regions of interest are objects (Cu particles) in its foreground. However, the particles having a color similar to the background color are buried in the background. Using the difference of two color backgrounds, we separated particles and background without dependent of background. The Otsu’ thresholding was employed to choose the threshold to maximize the degree of separation of the particles and background. The ratio of Cu to PVC pixels from mixed image was calculated by linear discriminant analysis. The error of PVC pixels resulted in zero, whereas the error of Cu pixels arose to 4.19%. Comparing the numbers of Cu and PVC pixels within the contour, the minority of the object were corrected to the majority of the object. The error of Cu pixels discriminated as PVC incorrectly became zero percent through this correction.
文摘When a gas expands through a convergent nozzle in which the ratio of the ambient to the stagnation pressures is higher than that of the critical one, the issuing jet from the nozzle is under-expanded. If a flat plate is placed normal to the jet at a certain distance from the nozzle, a detached shock wave is formed at a region between the nozzle exit and the plate. In general, supersonic moist air jet technologies with non-equilibrium condensation are very often applied to industrial manufacturing processes. In spite of the importance in major characteristics of the supersonic moist air jets impinging to a solid body, its qualitative characteristics are not known satisfactorily. In the present study, the effect of the non-equilibrium condensation on the under-expanded air jet impinging on a vertical flat plate is investigated numerically in the case with non-equilibrium condensation, frequency of oscillation for the flow field becomes larger than that without the non-equilibrium condensation, and amplitudes of static pressure become small compared with those of dry air. Furthermore, the numerical results are compared with experimental ones.
文摘When a Pressure wave propagates along a constant area straight tube and reaches at the open end, an impulsive wave is emitted outward from the tube exit toward the surrounding area and causes an impulsive noise like a sonic boom. In order to clarify the magnitude of an impulsive wave obtained by the discharge of a weak shock wave born an open end of a tube in relation to the noise problem and the industrial devices, the experimental and numerical investigations have been carried out for various strength of a shock wave. A simple open end shock tube with the flange at the tube exit.was used and the numerical calculation using the TVD scheme was performed. The effective equations which concerns with the magnitude of an impulsive wave generated by the emission of a shock wave have been obtained from the procedure of the open end correction based on the aeroacoustic theory and the numerical results. The influence of open end correction length and the diameter of a flange on the magnitude of an impulsive wave has been discussed.
文摘In the present study,a computational fluid dynamics work was performed to investigate the occurrence of the shock wave by condensation in supersonic moist air jet.The unsteady,compressible axisymmetric Navier-Stokes equation is solved by TVD(Total Variation Diminishing) scheme in this study.The numerical simulations have been performed for low pressure ratio and various humidities.The results show the occurrence of the shock wave in supersonic moist air jet for a low pressure ratio when Mach disk does not occur,depending on humidity of the air.
文摘In the present study, a computational fluid dynamics method has been applied to investigate the effects of initial degree of supersaturation at reservoir condition on under-expanded sonic jet structures, such as Mach disk location and diameter, barrel shock wave and jet boundary. The axisymmetric nozzle geometry investigated was a converging nozzle with straight part. As a result, it was found that the overpressures due to condensation generate and the characteristics of flow with generation of overpressure due to condensation in the jet were different from those without condensation.
文摘Electrical and structural properties of nanocrystalline solids of C80 fullerene encapsulated with a Lu3N cluster, Lu3N@C80, have been studied by measuring x-ray photoemission spectra, x-ray diffraction, and current-voltage characteristics of the Lu3N@C80/Au Schottky contact in the temperature range of 300 - 500 K. The nanocrystalline solid sample of Lu3N@C80 fullerene consists of grains characterized with an fcc structure and those grains become larger in size after pressing the powder sample at 1.25 GPa. The current-voltage characteristics measured at various temperatures showed that there are no significant dependences on both the Schottky barrier and the carrier mobility on electric field. The Schottky barrier of the Lu3N@C80/Au contact is determined to be 0.71 ± 0.04 eV.
文摘When the underexpanded supersonic jet impinges on the obstacle, it is well known that the self-induced flow os- cillation occurs. This oscillation depends on the pressure ratio in the flowfield, the position of an obstacle and is related with the noise problems of aeronautical and other industrial engineering. The characteristic and the mechanism of self-induced flow oscillation, have to be clarified to control various noise problems. But, it seems that the characteristics of the oscillated flowfield and the mechanism of an oscillation have to be more cleared to control the oscillation. This paper aims to clarify the effect of the pressure ratio and the obstacle position and the mechanism of self-induced flow oscillation by numerical analysis and experiment, when the underexpanded su- personic jet impinges on the cylindrical body. From the result of this study, it is clear that occurrence of the self-induced flow osciUation depends on the pressure balance in the flowfield.
