We have investigated experimentally the process of a droplet impact on a regular micro-grooved surface. The target surfaces are patterned such that micro-scale spokes radiate from the center, concentric circles, and p...We have investigated experimentally the process of a droplet impact on a regular micro-grooved surface. The target surfaces are patterned such that micro-scale spokes radiate from the center, concentric circles, and parallel lines on the polishing copper plate, using Quasi-LIGA molding technology. The dynamic behavior of water droplets impacting on these structured surfaces is examined using a high-speed camera, including the drop impact processes, the maximum spreading diameters, and the lengths and numbers of fingers at different values of Weber number. Experimental results validate that the spreading processes are arrested on all target surfaces at low velocity. Also, the experimental results at higher impact velocity demonstrate that the spreading process is conducted on the surface parallel to the micro-grooves, but is arrested in the direction perpendicular to the micro-grooves. Besides, the lengths of fingers increase observably, even when they are ejected out as tiny droplets along the groove direction, at the same time the drop recoil velocity is reduced by micro-grooves which are parallel to the spreading direction, but not by micro-grooves which are vertical to the spreading direction.展开更多
Data collected using the micro rain radar(MRR) situated in Jinan city, eastern China, were used to explore the altitudinal and temporal evolution of rainfall microphysical characteristics, and to analyze the bright ba...Data collected using the micro rain radar(MRR) situated in Jinan city, eastern China, were used to explore the altitudinal and temporal evolution of rainfall microphysical characteristics, and to analyze the bright band(BB) characteristics and hydrometeor classification. Specifically, a low-intensity and stable stratiform precipitation event that occurred from 0000 to0550 UTC 15 February 2015 and featured a BB was studied. During this event, the rainfall intensity was less than 2 mm h-1 at a height of 300 m, which was above the radar site level, so the errors caused by the vertical air motion could be ignored.The freezing height from the radiosonde matched well with the top of the BB observed by the MRR. It was also found that the number of 0.5–1 mm diameter drops showed no noticeable variation below the BB. The maximum fall velocity and the maximum gradient fall velocity(GFV) of the raindrops appeared at the bottom of the BB. Meanwhile, a method that uses the GFV and reflectivity to identify the altitude and the thickness of the BB was established, with which the MRR can provide a reliable and real-time estimation of the 0?C isotherm. The droplet fall velocity was used to classify the types of snow crystals above the BB. In the first 20 min of the selected precipitation event, graupel prevailed above the BB; and at an altitude of2000 m, graupel also dominated in the first 250 min. After 150 min, the existence of graupel and dendritic crystals with water droplets above the BB was inferred.展开更多
The flow properties of fine bubble mixture flows are investigated and reported. Few previous studies have focused on ultra-fine bubble (UFB) mixtures, which contain sub-micrometer sized bubbles. In this study, UFB mix...The flow properties of fine bubble mixture flows are investigated and reported. Few previous studies have focused on ultra-fine bubble (UFB) mixtures, which contain sub-micrometer sized bubbles. In this study, UFB mixtures of water and glycerol solution are passed through micro-sized slits and capillaries, and the resultant pressure drops are evaluated in comparison with those for water and aqueous glycerol alone. The experimentally measured pressure drop for slits (≤51 μm) and capillaries (≤81 μm) is less for UFB mixtures than for water and aqueous glycerol alone. This phenomenon is considered in terms of interface behavior and attributed to the electric interaction between an electric double layer and the UFBs. Furthermore, numerical observation for slip wall conditions is conducted, and the results for UFB mixtures agree with the predicted values for slip wall conditions.展开更多
This study evaluates the improvement of the radar Quantitative Precipitation Estimation (QPE) by involving microphysical processes in the determination of </span><i><span style="font-family:Verdana...This study evaluates the improvement of the radar Quantitative Precipitation Estimation (QPE) by involving microphysical processes in the determination of </span><i><span style="font-family:Verdana;">Z</span></i><span style="font-family:Verdana;">-</span><i><span style="font-family:Verdana;">R</span></i><span style="font-family:Verdana;"> algorithms. Within the framework of the AMMA campaign, measurements of an X-band radar (Xport), a vertical pointing Micro Rain Radar (MRR) to investigate microphysical processes and a dense network of rain </span><span style="font-family:Verdana;">gauges deployed in Northern Benin (West Africa) in 2006 and 2007 were</span><span style="font-family:Verdana;"> used as support to establish such estimators and evaluate their performance compared to other estimators in the literature. By carefully considering and correcting MRR attenuation and calibration issues, the </span><i><span style="font-family:Verdana;">Z</span></i><span style="font-family:Verdana;">-</span><i><span style="font-family:Verdana;">R</span></i><span style="font-family:Verdana;"> estimator developed </span><span style="font-family:Verdana;">with the contribution of microphysical processes and non-linear least</span></span><span style="font-family:Verdana;">-</span><span style="font-family:""><span style="font-family:Verdana;">squares adjustment proves to be more efficient for quantitative rainfall estimation and produces the best statistic scores than other optimal </span><i><span style="font-family:Verdana;">Z</span></i><span style="font-family:Verdana;">-</span><i><span style="font-family:Verdana;">R</span></i><span style="font-family:Verdana;"> algorithms in the literature. We also find that it gives results comparable to some polarimetric algorithms including microphysical information through DSD integrated parameter retrievals.展开更多
The mechanism of micro-hollow cathode discharge at atmospheric pressure is investigated through simulations using two-dimensional fluid model combined with a transport model for metastable atoms.In the simulations,ele...The mechanism of micro-hollow cathode discharge at atmospheric pressure is investigated through simulations using two-dimensional fluid model combined with a transport model for metastable atoms.In the simulations,electric potential,electric field,particle density,and mean electron energy of the discharge are calculated.The results show that the two characteristic regions of the discharge,i.e.cathode drop and negative glow can be distinguished in the simulation.The cathode drop is characterized by strong electric field and high mean electron energy,while quasi-neutral plasma of high density and exists in the negative glow.The peak value of electron density can reach the order of 1017cm-3.The electron temperature varies from several eV to tens of eV.The influence of cathode dimension on the discharge characteristics is also investigated.展开更多
In this paper, a novel micro drop solvent extraction technique jonied with low temperature ETV-ICP-AES for ultra trace element analysis is reported. The apparatus of micro drop solvent extraction was designed, and pre...In this paper, a novel micro drop solvent extraction technique jonied with low temperature ETV-ICP-AES for ultra trace element analysis is reported. The apparatus of micro drop solvent extraction was designed, and preliminary investigation was made for the extraction of ultra trace La by a micro drop of 0.05 mol/L PMBP-benzene(2 μL). It was found that 500-fold concentration of ultra-trace La in 1 mL solution was achieved in 0.2 mL of glass chamber by a single micro drop of PMBP-benzene suspended on the tip of a 10 μL of microsyringe. The future development of micro drop solvent extraction technique in atomic spectrometry was briefly discussed.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51109178)the Science and Technology Innovation Foundation of Northwestern Polytechnical University,China(Grant No.JC20120218)
文摘We have investigated experimentally the process of a droplet impact on a regular micro-grooved surface. The target surfaces are patterned such that micro-scale spokes radiate from the center, concentric circles, and parallel lines on the polishing copper plate, using Quasi-LIGA molding technology. The dynamic behavior of water droplets impacting on these structured surfaces is examined using a high-speed camera, including the drop impact processes, the maximum spreading diameters, and the lengths and numbers of fingers at different values of Weber number. Experimental results validate that the spreading processes are arrested on all target surfaces at low velocity. Also, the experimental results at higher impact velocity demonstrate that the spreading process is conducted on the surface parallel to the micro-grooves, but is arrested in the direction perpendicular to the micro-grooves. Besides, the lengths of fingers increase observably, even when they are ejected out as tiny droplets along the groove direction, at the same time the drop recoil velocity is reduced by micro-grooves which are parallel to the spreading direction, but not by micro-grooves which are vertical to the spreading direction.
基金sponsored by the National Natural Science Foundation of China (Grant Nos. 41475028 and 41530427)
文摘Data collected using the micro rain radar(MRR) situated in Jinan city, eastern China, were used to explore the altitudinal and temporal evolution of rainfall microphysical characteristics, and to analyze the bright band(BB) characteristics and hydrometeor classification. Specifically, a low-intensity and stable stratiform precipitation event that occurred from 0000 to0550 UTC 15 February 2015 and featured a BB was studied. During this event, the rainfall intensity was less than 2 mm h-1 at a height of 300 m, which was above the radar site level, so the errors caused by the vertical air motion could be ignored.The freezing height from the radiosonde matched well with the top of the BB observed by the MRR. It was also found that the number of 0.5–1 mm diameter drops showed no noticeable variation below the BB. The maximum fall velocity and the maximum gradient fall velocity(GFV) of the raindrops appeared at the bottom of the BB. Meanwhile, a method that uses the GFV and reflectivity to identify the altitude and the thickness of the BB was established, with which the MRR can provide a reliable and real-time estimation of the 0?C isotherm. The droplet fall velocity was used to classify the types of snow crystals above the BB. In the first 20 min of the selected precipitation event, graupel prevailed above the BB; and at an altitude of2000 m, graupel also dominated in the first 250 min. After 150 min, the existence of graupel and dendritic crystals with water droplets above the BB was inferred.
文摘The flow properties of fine bubble mixture flows are investigated and reported. Few previous studies have focused on ultra-fine bubble (UFB) mixtures, which contain sub-micrometer sized bubbles. In this study, UFB mixtures of water and glycerol solution are passed through micro-sized slits and capillaries, and the resultant pressure drops are evaluated in comparison with those for water and aqueous glycerol alone. The experimentally measured pressure drop for slits (≤51 μm) and capillaries (≤81 μm) is less for UFB mixtures than for water and aqueous glycerol alone. This phenomenon is considered in terms of interface behavior and attributed to the electric interaction between an electric double layer and the UFBs. Furthermore, numerical observation for slip wall conditions is conducted, and the results for UFB mixtures agree with the predicted values for slip wall conditions.
文摘This study evaluates the improvement of the radar Quantitative Precipitation Estimation (QPE) by involving microphysical processes in the determination of </span><i><span style="font-family:Verdana;">Z</span></i><span style="font-family:Verdana;">-</span><i><span style="font-family:Verdana;">R</span></i><span style="font-family:Verdana;"> algorithms. Within the framework of the AMMA campaign, measurements of an X-band radar (Xport), a vertical pointing Micro Rain Radar (MRR) to investigate microphysical processes and a dense network of rain </span><span style="font-family:Verdana;">gauges deployed in Northern Benin (West Africa) in 2006 and 2007 were</span><span style="font-family:Verdana;"> used as support to establish such estimators and evaluate their performance compared to other estimators in the literature. By carefully considering and correcting MRR attenuation and calibration issues, the </span><i><span style="font-family:Verdana;">Z</span></i><span style="font-family:Verdana;">-</span><i><span style="font-family:Verdana;">R</span></i><span style="font-family:Verdana;"> estimator developed </span><span style="font-family:Verdana;">with the contribution of microphysical processes and non-linear least</span></span><span style="font-family:Verdana;">-</span><span style="font-family:""><span style="font-family:Verdana;">squares adjustment proves to be more efficient for quantitative rainfall estimation and produces the best statistic scores than other optimal </span><i><span style="font-family:Verdana;">Z</span></i><span style="font-family:Verdana;">-</span><i><span style="font-family:Verdana;">R</span></i><span style="font-family:Verdana;"> algorithms in the literature. We also find that it gives results comparable to some polarimetric algorithms including microphysical information through DSD integrated parameter retrievals.
基金Project supported by National Science Foundation of China (11205046, 51077035), Science Foundation of Hebei Province(A2012201037), China Postdoctoral Science Foundation(2013M541195), Science Foundation of Hebei University (2011YYO 1, 2012-237).
文摘The mechanism of micro-hollow cathode discharge at atmospheric pressure is investigated through simulations using two-dimensional fluid model combined with a transport model for metastable atoms.In the simulations,electric potential,electric field,particle density,and mean electron energy of the discharge are calculated.The results show that the two characteristic regions of the discharge,i.e.cathode drop and negative glow can be distinguished in the simulation.The cathode drop is characterized by strong electric field and high mean electron energy,while quasi-neutral plasma of high density and exists in the negative glow.The peak value of electron density can reach the order of 1017cm-3.The electron temperature varies from several eV to tens of eV.The influence of cathode dimension on the discharge characteristics is also investigated.
文摘In this paper, a novel micro drop solvent extraction technique jonied with low temperature ETV-ICP-AES for ultra trace element analysis is reported. The apparatus of micro drop solvent extraction was designed, and preliminary investigation was made for the extraction of ultra trace La by a micro drop of 0.05 mol/L PMBP-benzene(2 μL). It was found that 500-fold concentration of ultra-trace La in 1 mL solution was achieved in 0.2 mL of glass chamber by a single micro drop of PMBP-benzene suspended on the tip of a 10 μL of microsyringe. The future development of micro drop solvent extraction technique in atomic spectrometry was briefly discussed.