The P2-type Na_(2/3)Fe_(1/2)Mn_(1/2)O_(2)materials were synthesized by an ultrasonic spray pyrolysis followed by solid-state sintering method.The structures,morphologies and electrochemical performances of Na_(2/3)Fe_...The P2-type Na_(2/3)Fe_(1/2)Mn_(1/2)O_(2)materials were synthesized by an ultrasonic spray pyrolysis followed by solid-state sintering method.The structures,morphologies and electrochemical performances of Na_(2/3)Fe_(1/2)Mn_(1/2)O_(2)materials were characterized thoroughly by means of X-ray diffractometer,scanning electron microscope and electrochemical charge/discharge instruments.Moreover,a thin layer of Al_(2)O_(3),which was formed on the surface of Na_(2/3)Fe_(1/2)Mn_(1/2)O_(2),can enhance the storage performance by preventing the formation of Na_(2)CO_(3)·H_(2)O,which is believed to enhance the electrochemical performances of Na_(2/3)Fe_(1/2)Mn_(1/2)O_(2)materials.This facile surface modification method may pave a way to synthesize advanced cathode materials for sodium-ion batteries.展开更多
Large-eddy simulation of spray combustion is under its rapid development.Different combustion models were used by different investigators.However,these models are less validated by detailed experimental data.In this p...Large-eddy simulation of spray combustion is under its rapid development.Different combustion models were used by different investigators.However,these models are less validated by detailed experimental data.In this paper,large-eddy simulation(LES)of ethanol spray-air combustion was made using an Eulerian-Lagrangian approach,a subgrid-scale kinetic energy stress model,and a filtered finite-rate combustion model,neglecting the sub-grid scale reaction rate.The simulation results are compared with experimental dada in the literature and validated in detail.The LES obtained statistically averaged gas temperature is in much better agreement with the experimental results than Reynolds averaged(RANS)modeling using the most complex probability density function(PDF)equation combustion model.The instantaneous LES results show the coherent structures of the shear region near the high-temperature flame zone and the fuel vapor concentration map,indicating that the droplets are concentrated in this shear region.The instantaneous temperature,oxygen and carbon dioxide concentration maps show the close interaction between the coherent structures and the combustion reaction.展开更多
In order to further clarify the spraying performance of siphonic nozzle, the spray rate of siponic cone nozzle with aperture of 1.0 mm was determined at 15 different air pressure levels and 12 gravity drop levels, and...In order to further clarify the spraying performance of siphonic nozzle, the spray rate of siponic cone nozzle with aperture of 1.0 mm was determined at 15 different air pressure levels and 12 gravity drop levels, and DPS and SPSS were used to make the difference analysis and modeling, which clarified the relationship between the spray rate of the siphonic cone nozzle with aperture of 1.0 mm and air pressure and gravity drop, getting the regression equation of Y=406.854P＋ 1.904G＋77.524. The study could provide a theoretical basis for the optimization and improvement of plant protection spraying equipment.展开更多
The measurement of droplet velocities in Diesel sprays close to the nozzle is important because of the complexity of in-nozzle flow, spray break-up and evaporation. However, the measurement of droplet velocities in th...The measurement of droplet velocities in Diesel sprays close to the nozzle is important because of the complexity of in-nozzle flow, spray break-up and evaporation. However, the measurement of droplet velocities in the dense region of Diesel sprays is very difficult or impossible by means of widely used laser diagnostic techniques, in particular under engine-like high-pressure and high-temperature conditions. The limitations of phase Doppler anemometry （PDA） and particle image velocimetry （PIV） prevent the application to the ultra-dense region of the spray. It was demonstrated that these problems can be greatly reduced by the laser flow tagging （LFT） technique. It was also demonstrated recently that LFT measurements can be conducted in clustered Diesel jets with improved spatial resolution and increased number of simultaneous measurements in the near-nozzle region. In the present work, the nozzle design, the temperature and pressure of the ambient air, and the fuel rail pressure are varied, in order to investigate the influence on the near-nozzle jet velocity and the underlying physical mechanisms.展开更多
During pesticide spraying, some of the smallest or slowest droplets do not reach the target and may contribute to spray drift. Therefore, it is important to characterize droplet size and velocity close to the nozzle e...During pesticide spraying, some of the smallest or slowest droplets do not reach the target and may contribute to spray drift. Therefore, it is important to characterize droplet size and velocity close to the nozzle exit. The aim of this study was to contribute to the comprehension of spray formation. Surfactant influence on spray characteristics was studied by comparing water spray with sprays containing three different surfactants, Two nozzles including a classical hollow cone nozzle ATR （Albuz, France） and an air-induced hollow cone nozzle TVI which is a low-drift nozzle （Albuz, France） were chosen. Radial profiles of the axial velocity component and Sauter mean diameter at two axial distances from the nozzle exit were measured using a Phase Doppler Particle Analyzer （PDPA）. Results showed that sprays issued from ATR and TVI nozzles were very different, even when water was sprayed. Effect of adding surfactant depended on the nozzle type. Sheet thickness was reduced by adding Elton and Heliosol regardless of the nozzle type. They reduced spray angle of ATR nozzle spray but did not affect that of YVI nozzle. Break-Thru has a slight effect when sprayed through the ATR nozzle, but it has the most pronounced effect on the SMD when sprayed through the TVI nozzle.展开更多
In a gas turbine engine combustor, highly swiding combustion is usually adopted to stabilize flame and reduce pollutant emissions. Swirl cup, as an air blast atomizer, is widely used to provide a uniform presentation ...In a gas turbine engine combustor, highly swiding combustion is usually adopted to stabilize flame and reduce pollutant emissions. Swirl cup, as an air blast atomizer, is widely used to provide a uniform presentation of fuel droplets to the combustor dome. This paper investigated the effect of secondary swirler on the flow field down- stream of the swirl cup using particle image velocimetry （PIV）. Three swirl cups＇ non-reacting flow field were studied： case A, B and C with secondary swirler vane angle 53°, 60° and 68° respectively. Detailed mean and transient velocities and vorticity in the center plane were obtained. From the PIV results, a sharp contrast flow field was obtained for case A to other two cases due to the lower secondary swirling intensity. The recirculation zone is collapsed in disorder for the case A. Ignition tests of the three cups were completed in a single cup com- bustor. In general, the ignition performance increases with the increasing of the secondary swirling intensity. For case A, the ignition performance is very unstable and has much randomness and there is no clear lean ignition boundary can be generated. This work can further understand the swirl behavior and ignition mechanism.展开更多
A theoretical model is developed to predict the upper limit heat transfer between a stack of parallel plates subject to multiphase cooling by air-mist flow.The model predicts the optimal separation distance between th...A theoretical model is developed to predict the upper limit heat transfer between a stack of parallel plates subject to multiphase cooling by air-mist flow.The model predicts the optimal separation distance between the plates based on the development of the boundary layers for small and large separation distances,and for dilute mist conditions.Simulation results show the optimal separation distance to be strongly dependent on the liquid-to-air mass flow rate loading ratio,and reach a limit for a critical loading.For these dilute spray conditions,complete evaporation of the droplets takes place.Simulation results also show the optimal separation distance decreases with the increase in the mist flow rate.The proposed theoretical model shall lead to a better understanding of the design of fins spacing in heat exchangers where multiphase spray cooling is used.展开更多
基金financially supported by the Natural Science Foundation of Hunan Province,China(No.2020JJ5755)the National Natural Science Foundation of China(Nos.51804344,51704332,51874360)the Innovation and Entrepreneurship Project of Hunan Province,China(No.2018GK5026)。
文摘The P2-type Na_(2/3)Fe_(1/2)Mn_(1/2)O_(2)materials were synthesized by an ultrasonic spray pyrolysis followed by solid-state sintering method.The structures,morphologies and electrochemical performances of Na_(2/3)Fe_(1/2)Mn_(1/2)O_(2)materials were characterized thoroughly by means of X-ray diffractometer,scanning electron microscope and electrochemical charge/discharge instruments.Moreover,a thin layer of Al_(2)O_(3),which was formed on the surface of Na_(2/3)Fe_(1/2)Mn_(1/2)O_(2),can enhance the storage performance by preventing the formation of Na_(2)CO_(3)·H_(2)O,which is believed to enhance the electrochemical performances of Na_(2/3)Fe_(1/2)Mn_(1/2)O_(2)materials.This facile surface modification method may pave a way to synthesize advanced cathode materials for sodium-ion batteries.
基金Supported by the National Natural Science Foundation of China(5073600,51266008)the Research Grant Council of Hong Kong(5105/08E,B-Q10H)
文摘Large-eddy simulation of spray combustion is under its rapid development.Different combustion models were used by different investigators.However,these models are less validated by detailed experimental data.In this paper,large-eddy simulation(LES)of ethanol spray-air combustion was made using an Eulerian-Lagrangian approach,a subgrid-scale kinetic energy stress model,and a filtered finite-rate combustion model,neglecting the sub-grid scale reaction rate.The simulation results are compared with experimental dada in the literature and validated in detail.The LES obtained statistically averaged gas temperature is in much better agreement with the experimental results than Reynolds averaged(RANS)modeling using the most complex probability density function(PDF)equation combustion model.The instantaneous LES results show the coherent structures of the shear region near the high-temperature flame zone and the fuel vapor concentration map,indicating that the droplets are concentrated in this shear region.The instantaneous temperature,oxygen and carbon dioxide concentration maps show the close interaction between the coherent structures and the combustion reaction.
基金Supported by the Special Key Fund for Science and Technology of Anhui Province(15CZZ03132)the Special Fund for Talent Development of Anhui Province(13C1109)the Agricultural Science and Technology Innovation Fund Project of Anhui Province(16A1132)~~
文摘In order to further clarify the spraying performance of siphonic nozzle, the spray rate of siponic cone nozzle with aperture of 1.0 mm was determined at 15 different air pressure levels and 12 gravity drop levels, and DPS and SPSS were used to make the difference analysis and modeling, which clarified the relationship between the spray rate of the siphonic cone nozzle with aperture of 1.0 mm and air pressure and gravity drop, getting the regression equation of Y=406.854P＋ 1.904G＋77.524. The study could provide a theoretical basis for the optimization and improvement of plant protection spraying equipment.
文摘The measurement of droplet velocities in Diesel sprays close to the nozzle is important because of the complexity of in-nozzle flow, spray break-up and evaporation. However, the measurement of droplet velocities in the dense region of Diesel sprays is very difficult or impossible by means of widely used laser diagnostic techniques, in particular under engine-like high-pressure and high-temperature conditions. The limitations of phase Doppler anemometry （PDA） and particle image velocimetry （PIV） prevent the application to the ultra-dense region of the spray. It was demonstrated that these problems can be greatly reduced by the laser flow tagging （LFT） technique. It was also demonstrated recently that LFT measurements can be conducted in clustered Diesel jets with improved spatial resolution and increased number of simultaneous measurements in the near-nozzle region. In the present work, the nozzle design, the temperature and pressure of the ambient air, and the fuel rail pressure are varied, in order to investigate the influence on the near-nozzle jet velocity and the underlying physical mechanisms.
文摘During pesticide spraying, some of the smallest or slowest droplets do not reach the target and may contribute to spray drift. Therefore, it is important to characterize droplet size and velocity close to the nozzle exit. The aim of this study was to contribute to the comprehension of spray formation. Surfactant influence on spray characteristics was studied by comparing water spray with sprays containing three different surfactants, Two nozzles including a classical hollow cone nozzle ATR （Albuz, France） and an air-induced hollow cone nozzle TVI which is a low-drift nozzle （Albuz, France） were chosen. Radial profiles of the axial velocity component and Sauter mean diameter at two axial distances from the nozzle exit were measured using a Phase Doppler Particle Analyzer （PDPA）. Results showed that sprays issued from ATR and TVI nozzles were very different, even when water was sprayed. Effect of adding surfactant depended on the nozzle type. Sheet thickness was reduced by adding Elton and Heliosol regardless of the nozzle type. They reduced spray angle of ATR nozzle spray but did not affect that of YVI nozzle. Break-Thru has a slight effect when sprayed through the ATR nozzle, but it has the most pronounced effect on the SMD when sprayed through the TVI nozzle.
文摘In a gas turbine engine combustor, highly swiding combustion is usually adopted to stabilize flame and reduce pollutant emissions. Swirl cup, as an air blast atomizer, is widely used to provide a uniform presentation of fuel droplets to the combustor dome. This paper investigated the effect of secondary swirler on the flow field down- stream of the swirl cup using particle image velocimetry （PIV）. Three swirl cups＇ non-reacting flow field were studied： case A, B and C with secondary swirler vane angle 53°, 60° and 68° respectively. Detailed mean and transient velocities and vorticity in the center plane were obtained. From the PIV results, a sharp contrast flow field was obtained for case A to other two cases due to the lower secondary swirling intensity. The recirculation zone is collapsed in disorder for the case A. Ignition tests of the three cups were completed in a single cup com- bustor. In general, the ignition performance increases with the increasing of the secondary swirling intensity. For case A, the ignition performance is very unstable and has much randomness and there is no clear lean ignition boundary can be generated. This work can further understand the swirl behavior and ignition mechanism.
文摘A theoretical model is developed to predict the upper limit heat transfer between a stack of parallel plates subject to multiphase cooling by air-mist flow.The model predicts the optimal separation distance between the plates based on the development of the boundary layers for small and large separation distances,and for dilute mist conditions.Simulation results show the optimal separation distance to be strongly dependent on the liquid-to-air mass flow rate loading ratio,and reach a limit for a critical loading.For these dilute spray conditions,complete evaporation of the droplets takes place.Simulation results also show the optimal separation distance decreases with the increase in the mist flow rate.The proposed theoretical model shall lead to a better understanding of the design of fins spacing in heat exchangers where multiphase spray cooling is used.
