The particle concentration inside a cyclone separator at different operation parameters was simulated with the FLUENT software. The Advanced Reynolds Stress Model （ARSM） was used in gas phase turbulence modeling. St...The particle concentration inside a cyclone separator at different operation parameters was simulated with the FLUENT software. The Advanced Reynolds Stress Model （ARSM） was used in gas phase turbulence modeling. Stochastic Particle Tracking Model （SPTM） and the Particle-Source-In-Cell （PSIC） method were adopted for particles computing. The interaction between particles and the gas phase was also taken into account. The numerical simulation results were in agreement with the experimental data. The simulation revealed that an unsteady spiral dust strand appeared near the cyclone wall and a non-axi-symmetrical dust ring appeared in the annular space and under the cover plate of the cyclone. There were two regions in the radial particle concentration distribution, in which particle concentration was low in the inner region （r/R≤0.75） and increased greatly in the outer region （r/R〉0.75）. Large particles generally had higher concentration in the near-wall region and small particles had higher concentration in the inner swirling flow region. The axial distribution of particle concentration in the inner swirling flow （r/R≤0.3） region showed that there existed serious fine particle entrainment within the height of 0.SD above the dust discharge port and a short-cut flow at a distance of about 0.25D below the entrance of the vortex finder. The dimensionless concentration in the high-concentration region increased obviously in the upper part of the cyclone separation space when inlet particle loading was large. With increasing gas temperature, the particle separation ability of the cyclone was obviously weakened.展开更多
Adsorption/desorption in a new Zn（Ⅱ）-TiO2 adsorption system was investigated at different particle concentrations （Cp）. TEM, SEM and XRD analyses revealed that the TiO2 particles were an aggregation of nano-sized...Adsorption/desorption in a new Zn（Ⅱ）-TiO2 adsorption system was investigated at different particle concentrations （Cp）. TEM, SEM and XRD analyses revealed that the TiO2 particles were an aggregation of nano-sized （approximately 10 nm） pure anatase-type TiO2. Adsorption experiments were carried out with particle concentrations of 100, 400 and 1000 mg/L, and their adsorption isotherms were found to decline successively, showing an obvious Cp effect. Desorption experiments indicated that adsorption in this system was irreversible, and the irreversibility increased with increasing Cp. These phenomena could be explained by the MEA （metastable equilibrium adsorption） theory and the Cp effect could be modeled well with an MEA-Freundlich-type Cp effect isotherm equation. This study may heln understand environmental behavior of contaminants on ultrafine natural particles.展开更多
A cyclone dust collector is applied in many industries. Especially the axial flow cyclone is the mostsimple construction and it keeps high reliability for maintenance. On the other hand, the collectionefficiency of th...A cyclone dust collector is applied in many industries. Especially the axial flow cyclone is the mostsimple construction and it keeps high reliability for maintenance. On the other hand, the collectionefficiency of the cyclone depends not only on the inlet gas velocity but also on the feed particle concentration. The collection efficiency increases with increasing feed particle concentration. However untilnow the problem of how to estimate the collection efficiency depended on the feed particle concentrationis remained except the investigation by Muschelknautz & Brunner~[6]. Therefore in this paper one ofthe estimate method for the collection efficiency of the axial flow cyclones is proposed. The applicationto the geometrically similar type of cyclone of the body diameters D_1=30, 50, 69 and 99 mm showedin good agreement with the experimental results of the collection efficiencies which were described indetail in the paper by Ogawa & Sugiyama~[8].展开更多
During the 2012 Lanzhou International Marathon, the local government made a significant effort to improve traffic conditions and air quality by implementing traffic restriction measures. To evaluate the direct effect ...During the 2012 Lanzhou International Marathon, the local government made a significant effort to improve traffic conditions and air quality by implementing traffic restriction measures. To evaluate the direct effect of these measures on urban air quality, especially particle concentrations and their size distributions, atmospheric particle size distributions （0.5-20μm） obtained using an aerodynamic particle sizer （model 3321, TSI, USA） in June 2012 were analyzed. It was found that the particle number, surface area and volume concentrations for size range 0.5-10 μm were （15.0±2.1） cm-3, （11.8±2.6） μm2/cm3 and （1.9±0.6） μm2/cm3, respectively, on the traffic-restricted day （Sunday）, which is 63.2%, 53.0% and 47.2% lower than those on a normal Sunday. For number and surface area concentrations, the most affected size range was 0.5-0.7 and 0.5-0.8 μm, respectively, while for volume concentration, the most affected size ranges were 0.5-0.8, 1.7-2.0 and 5.0-5.4 μm. Number and volume concentrations of particles in size range 0.5-1.0μm correlated well with the number of non-CNG （Compressed Natural Gas） powered vehicles, while their correlation with the number of CNG-powered vehicles was very low, suggesting that reasonable urban traffic controls along with vehicle technology improvements could play an important role in improving urban air quality.展开更多
The seasonal transport of the Saharan dust to the West African region, near the Gulf of Guinea, during northem winter has been studied over 12 years. Using an optical particle counter, the dust aerosols in the diamete...The seasonal transport of the Saharan dust to the West African region, near the Gulf of Guinea, during northem winter has been studied over 12 years. Using an optical particle counter, the dust aerosols in the diameter range 0.5-25 μm have been sampled at Kumasi （6040＇ N, l°34＇ W） in Ghana during the winter months of January-February from 1997 to 2009. The settling atmospheric dust particles observed during the peak Harmattan and the background Harmattan periods are analysed for the mean particle size, number and mass concentrations as well as the particle size-frequency. It is shown that the average daily particle diameter, number and mass concentrations obtained in the peak Harmattan periods are 1.57 ± 0.54 μm, 50 ± 25 particles/cm3 and 1,130 ± 994 μg/m3, respectively, while for the background Harmattan these values are correspondingly, 1.31 ±0.31 μm, 32 ±12 particles/cm3 and 576 ±429 μg/m3, respectively. These experimental results will be useful for the design of ambient air-filters and for understanding the West African climate change.展开更多
Particle size distribution of 12-500 nm was measured at Mt. Waliguan, China Global Atmosphere Watch Baseline Observatory, from Aug. in 2005 to May in 2007.72-hr back-trajectories at 100-m arrival height above ground l...Particle size distribution of 12-500 nm was measured at Mt. Waliguan, China Global Atmosphere Watch Baseline Observatory, from Aug. in 2005 to May in 2007.72-hr back-trajectories at 100-m arrival height above ground level for the same period were calculated at 6：00, 12：00, and 21：00 （Beijing Time） for each day using the Hybrid Single-Particle Lagrangian Integrated Trajectory （HYSPLIT-4） model developed by NOAA/ARL. It was found that air mass sources significantly impact particle number concentration and size distribution at Mt. Waliguan. Cluster analysis of back-trajectories show that higher Aitken mode particle number concentration was observed when air masses came from or passed by the northeastern section of Mt. Waliguan, with short trajectory length. High number concentration of nucleation mode was associated with air masses from clean regions, with long trajectory length.展开更多
The TSI-3321 APS was used to measure concentration of atmospheric particulates in Ranjiaba region of Yubei District in Chongqing City during March 21- 29,2014,and the temporal variations in the hourly average mass and...The TSI-3321 APS was used to measure concentration of atmospheric particulates in Ranjiaba region of Yubei District in Chongqing City during March 21- 29,2014,and the temporal variations in the hourly average mass and number concentration and median particle diameter of PM10 and PM2.5 as well as their correlation with relative humidity were analyzed. The results showed that the three indicators of PM10 and PM2.5 except for the mass concentration correlated with relative humidity,of which the correlation between the mass median particle diameter and relative humidity was the best. The correlation coefficient R^2 between the mass median particle diameter of PM10（ PM2.5） and relative humidity was up to 0. 943（ 0. 832）. Therefore,relative humidity and pressure are key impact factors of indicators of particles.展开更多
Direct measurement of slip length is based on the measured fluid velocity near solid boundary. However, previous micro particle image velocimetry/particle tracking velocimetry （microPIV/PTV） measurements have report...Direct measurement of slip length is based on the measured fluid velocity near solid boundary. However, previous micro particle image velocimetry/particle tracking velocimetry （microPIV/PTV） measurements have reported surprisingly large measured near-wall velocities of pressure-driven flow in apparent contradiction with the no-slip hy-pothesis and experimental results from other techniques. To better interpret the measured results of the microPIV/PTV, we performed velocity profile measurements near a hy-drophilic wall （z = 0.25-1.5 μm） with two sizes of tracer particles （φ 50 nm and φ200 nm）. The experimental results indicate that, at less than 1 μm from the wall, the deviations between the measured velocities and no-slip theoretical values obviously decrease from 93% of φ200 nm particles to 48% of φ50 nm particles. The Boltzmann-like exponential measured particle concentrations near wall were found. Based on the non linear Boltzmann distribution of particle concentration and the effective focus plane thickness, we illustrated the reason of the apparent velocity increase near wall and proposed a method to correct the measured velocity profile. By this method, the deviations between the corrected measured velocities and the no-slip theoretical velocity decrease from 45.8% to 10%, and the measured slip length on hy-drophilic glass is revised from 75 nm to 16 nm. These results indicated that the particle size and the biased particle concentration distribution can significantly affect near wall velocity measurement via microPIV/PTV, and result in larger measured velocity and slip length close to wall.展开更多
The Reynolds-averaged general dynamic equation(RAGDE)for the nanoparticle size distribution function is derived,including the contribution to particle coagulation resulting from the fluctuating concentration.The equat...The Reynolds-averaged general dynamic equation(RAGDE)for the nanoparticle size distribution function is derived,including the contribution to particle coagulation resulting from the fluctuating concentration.The equation together with that of a turbulent gas flow is solved numerically in the turbulent flow of a ventilation chamber with a jet on the wall based on the proposed model relating the fluctuating coagulation to the gradient of mean concentration.Some results are compared with the experimental data.The results show that the proposed model relating the fluctuating coagulation to the gradient of mean concentration is reasonable,and it is necessary to consider the contribution to coagulation resulting from the fluctuating concentration in such a flow.The changes of the particle number concentration M_(0) and the geometric mean diameter dg are more obvious in the core area of the jet,but less obvious in other areas.With the increase in the initial particle number concentration m00,the values of M_(0) and the standard deviation of the particle sizeσdecrease,but the value of d_(g) increases.The decrease in the initial particle diameter leads to the reduction of M_(0) andσand the increase in d_(g).With the increase in the Reynolds number,particles have few chances of collision,and hence the coagulation rate is reduced,leading to the increase in M_(0) andσand the decrease in d_(g).展开更多
During the Austral summer of 1996/1997, the First Chinese Antarctic Inland Expedition reached the inland area about 330 km along the direction around 76°E from Zhongshan Station, and collected 84 surface snow...During the Austral summer of 1996/1997, the First Chinese Antarctic Inland Expedition reached the inland area about 330 km along the direction around 76°E from Zhongshan Station, and collected 84 surface snow samples at an interval of 4 km . Micro particle analysis of the samples indicates that the micro particle concentration apparently decreases with the increasing of altitude, and the amplitudes of micro particle concentration is much larger in the lower altitude than in the higher altitude. Further analysis of grain size distributions of micro particle, percentage of micro particles from different sources and variations with altitude suggest that micro particles in this area are from a considerably dominant source. Although this area is controlled by polar easterly wind and katabatic wind, transportation and deposition of the micro particles are mainly influenced by marine transportation in coastal area.展开更多
The cyclone separator is an important separation device.This paper presents a new type of embedded two-stage cyclone,which includes a 2 nd-stage cyclone(internal traditional cyclone)with multiple inlets and a 1 st-sta...The cyclone separator is an important separation device.This paper presents a new type of embedded two-stage cyclone,which includes a 2 nd-stage cyclone(internal traditional cyclone)with multiple inlets and a 1 st-stage cyclone(outer cylinder)that unifies the 2 nd-stage cyclone inlets into one inlet.The Taguchi experimental method was used to study the two-stage cyclone separator’s inlet area on its performance.Studies have shown that the increase of the 1 st-stage cyclone inlet area and the increase in the number of 2 nd-stage cyclone inlets(N)positively affect reducing the pressure drop and a negative effect on efficiency.It is recommended to use 2 S(the original 1 st-stage cyclone inlet area)of the 1 st-stage cyclone inlet area and 2 N of the 2 nd-stage cyclone inlets when separating fine particles.Compared with a traditional cyclone,the pressure drop is reduced by 1303 Pa,the mass separation efficiency(Eq)is increased by 0.56%,and the number separation efficiency(En)is increased by 2.05%.When separating larger particles,it is recommended to use 2 S of the 1 st-stage cyclone inlet area and 4 N of the 2 nd-stage cyclone inlets.Compared with a traditional cyclone,although Endecreases slightly,the pressure drop is reduced by 3055 Pa,and the Eqis increased by 0.56%.The research results provide new insight into the design of the cyclone.展开更多
Based on the analysis of spectrum characteristics of intensity fluctuations while light beams pass through stack gas flow in an industrial setting, this paper puts emphasis upon discussing the spectrum of optical inte...Based on the analysis of spectrum characteristics of intensity fluctuations while light beams pass through stack gas flow in an industrial setting, this paper puts emphasis upon discussing the spectrum of optical intensity fluctuations by the variety of particle concentration in stack gas flow. This paper also gives the primary theoretical explanation of the measurement results in the stack of coal-fired utility boilers. Meanwhile, the cross-correlation formula is given as the theoretical basis of velocity measurement by using particle concentration scintillation.展开更多
In order to solve the problem that the vulcanizing agent utilization rate is low and the dilution effect of copper slag is poor,the vortex stirring dilution method was used to improve the conditions of the dilution ki...In order to solve the problem that the vulcanizing agent utilization rate is low and the dilution effect of copper slag is poor,the vortex stirring dilution method was used to improve the conditions of the dilution kinetics and copper recovery.The water model was used to simulate the effect of copper slag dilution.Under the premise of keeping the Reynolds number consistent,silicone oil and glass beads were used instead of copper slag and vulcanizing agent.Based on the relationship between voltage and concentration,the PC6D dual-channel particle concentration measuring instrument was used to study the stirring speed and the insertion depth of the stirring paddle in model experiments,and the suitable conditions were speed 250 rpm and insertion depth 70 mm.The fire dilution of copper slag was done under the conditions.After stirring and sedimentation,the Fe_(3)O_(4) in slag decreased from 22.58% to 4.65%,and the copper content of the slag decreased from 2.94% to 0.34%.The copper recovery was 88.44%.展开更多
Indoor environment separated with down-feed air curtain was numerically simulated and experimen-tally researched. Indoor airflow and temperature fields separated with air curtain were numerically simulated. Re-sults s...Indoor environment separated with down-feed air curtain was numerically simulated and experimen-tally researched. Indoor airflow and temperature fields separated with air curtain were numerically simulated. Re-sults show that both polluted airflow and thermal air current can be separated with a down-feed air curtain to pre-vent contaminants from spreading in the room space. In a test chamber, the smoke of burning Tibetan incense served as the source of contaminants, and the probe test shows that 1.0 μm is the prevailing diameter of the smoke particles. During the release of the smoke, the particle concentration of the indoor air was tested with a laser particle counter at the points of three different heights from the floor when the air curtain was running or not. Experimental results show that the higher the test point is located, the lower the particle concentration is, implying that the sepa-rating or isolating effect decreases as the air velocity of the curtain reduces along with the height descends. Accord-ing to both simulation and experimental results, down-feed air curtain can separate indoor environment effectively when the supply air velocity of air curtain is not less than 3 m/s. In order to strengthen separation effect, it is sug-gested that the supply air velocity be speeded up to 5 m/s.展开更多
The paper presents a simple model for outdoor air contaminant transmission into occupied rooms. In the model, several factors such as filtration, ventilation, deposition, re-emission, outdoor concentration and indoor ...The paper presents a simple model for outdoor air contaminant transmission into occupied rooms. In the model, several factors such as filtration, ventilation, deposition, re-emission, outdoor concentration and indoor sources are included. The model results show that the air exchange rate plays an important role in the transmission of outdoor contaminants into the indoor environment. The model shows that increasing the value of the filtration efficiency decreases the mass concentration of indoor particles. In addition, if outdoor aerosol particles have a periodic behaviour, indoor aerosol particles also behave periodically but smoother. Indoor sources are found to be able to increase indoor concentrations greatly and continuously.展开更多
An approach is developed to examine the mean and uncertainty of thermal conductivity of a heterogeneous multiparticle system,where the particle concentration or void fraction is treated as a truncated fractal distribu...An approach is developed to examine the mean and uncertainty of thermal conductivity of a heterogeneous multiparticle system,where the particle concentration or void fraction is treated as a truncated fractal distribution.The truncated fractal distribution is then integrated into the Maxwell model,which is equivalent to a cell model in which the multiparticle system is conceptualized as a spherical fluid cell that envelopes a solid particle.The developed mean thermal conductivity is compared with four experimental data sets of liquid-saturated media from the literature.The effect of fractal characteristics is quantified and discussed.Incorporating particle concentration or void fraction truncated fractal distribution can better capture scatters in the experimental results.The thermal conductivity and its standard deviation decrease with increasing fractal dimensions.When the void fraction is truncated fractal,the uncertainty increases mostly in the low mean void fraction range and drops more quickly with the increasing mean void fraction compared to the case where the particle concentration is truncated fractal.In a typical case of multiparticle system when the solid particles are more conductive than the fluid,the faster increase rate of standard deviation with the ratio of solid over fluid conductivities occurs when the mean void fraction is smaller.展开更多
The time series of indoor and outdoor particle number concentrations in a naturally ventilated residential building in Xi＇an were tested simultaneously for 7 days in summer. The relationships between indoor and outdo...The time series of indoor and outdoor particle number concentrations in a naturally ventilated residential building in Xi＇an were tested simultaneously for 7 days in summer. The relationships between indoor and outdoor concentrations were examined and discussed, and linear regression analysis was employed to correlate the indoor and outdoor concentrations. The diurnal cycles of indoor and outdoor particle concentrations of different particle size ranges all showed positive correlations between indoor and outdoor number concentrations, The I/O ratios of number concentrations varied with the increase of particle size in the range of 0.89 （±0.19） to 0.99 （±0.15）.展开更多
A model for measuring aerosol mass concentration by an optical particle counter is presented using the conception of the average mass. In this model, to understand the meaning of the pulse height distribution of parti...A model for measuring aerosol mass concentration by an optical particle counter is presented using the conception of the average mass. In this model, to understand the meaning of the pulse height distribution of particles which is used to inverse mass concentration, the relationship among intensity distribution in the optical sensing volume, particle shape, and the pulse height distribution is discussed. To solve the instability of the equivalent factor, a novel two-step calibration method is proposed. The experimental results demonstrate that mass concentrations calculated by the model are in good agreement with those measured by a norm-referenced instrument. For samples of soot and air, the slopes of fitting lines of data points are 0.9582 and 0.9220, and the correlation coefficients are 0.9991 and 0.9965, respectively.展开更多
In order to reveal the influence of forced ventilation on the dispersion of droplets ejected from roadheader-mounted external sprayer,the paper studies the air-flowing field and the droplet distribution under the cond...In order to reveal the influence of forced ventilation on the dispersion of droplets ejected from roadheader-mounted external sprayer,the paper studies the air-flowing field and the droplet distribution under the condition of gentle breeze and normal forced ventilation in heading face using the particle tracking technology of computational fluid dynamics(CFD).The results show that air-flowing tendency in the same section presents great comparability in the period of gentle breeze and forced ventilation,and the difference mainly embodies in the different wind velocity.The influence of ventilation on the dispersion of droplets is faint under the gentle breeze condition.The droplet can be evenly distributed around the cutting head.However,under the normal forced ventilation,a large number of droplets will drift to the return air side.At the same time,droplet clusters are predominantly presented in the lower part of windward side and the middle of the leeward side around the cutting head.In contrast,the droplet concentration in other parts around cutting head decreases a lot and the droplets are unable to form close-grained mist curtain.So the dust escape channel is formed.In addition,the simulation results also reveal that the disturbance of air flow on the droplet distribution can be effectively relieved when using ventilation duct with Coanda effect(VDCE).Field experiment results show that the dust suppression efficiency of total dust and respirable dust increases respectively by 10.5%and 9.3%when using VDCE,which proves that it can weaken the influence of airflow on droplet dispersion.展开更多
基金Supported by the National Key Project of Basic Research of the Ministry for Science and Technology of P. R. China (Grant No. 2005CB22120103)
文摘The particle concentration inside a cyclone separator at different operation parameters was simulated with the FLUENT software. The Advanced Reynolds Stress Model （ARSM） was used in gas phase turbulence modeling. Stochastic Particle Tracking Model （SPTM） and the Particle-Source-In-Cell （PSIC） method were adopted for particles computing. The interaction between particles and the gas phase was also taken into account. The numerical simulation results were in agreement with the experimental data. The simulation revealed that an unsteady spiral dust strand appeared near the cyclone wall and a non-axi-symmetrical dust ring appeared in the annular space and under the cover plate of the cyclone. There were two regions in the radial particle concentration distribution, in which particle concentration was low in the inner region （r/R≤0.75） and increased greatly in the outer region （r/R〉0.75）. Large particles generally had higher concentration in the near-wall region and small particles had higher concentration in the inner swirling flow region. The axial distribution of particle concentration in the inner swirling flow （r/R≤0.3） region showed that there existed serious fine particle entrainment within the height of 0.SD above the dust discharge port and a short-cut flow at a distance of about 0.25D below the entrance of the vortex finder. The dimensionless concentration in the high-concentration region increased obviously in the upper part of the cyclone separation space when inlet particle loading was large. With increasing gas temperature, the particle separation ability of the cyclone was obviously weakened.
基金Project supported by the National Natural Science Foundation of China(No.20537020)the "Hundred Talent Scientist Program" of the Chinese Academy of Sciences.
文摘Adsorption/desorption in a new Zn（Ⅱ）-TiO2 adsorption system was investigated at different particle concentrations （Cp）. TEM, SEM and XRD analyses revealed that the TiO2 particles were an aggregation of nano-sized （approximately 10 nm） pure anatase-type TiO2. Adsorption experiments were carried out with particle concentrations of 100, 400 and 1000 mg/L, and their adsorption isotherms were found to decline successively, showing an obvious Cp effect. Desorption experiments indicated that adsorption in this system was irreversible, and the irreversibility increased with increasing Cp. These phenomena could be explained by the MEA （metastable equilibrium adsorption） theory and the Cp effect could be modeled well with an MEA-Freundlich-type Cp effect isotherm equation. This study may heln understand environmental behavior of contaminants on ultrafine natural particles.
文摘A cyclone dust collector is applied in many industries. Especially the axial flow cyclone is the mostsimple construction and it keeps high reliability for maintenance. On the other hand, the collectionefficiency of the cyclone depends not only on the inlet gas velocity but also on the feed particle concentration. The collection efficiency increases with increasing feed particle concentration. However untilnow the problem of how to estimate the collection efficiency depended on the feed particle concentrationis remained except the investigation by Muschelknautz & Brunner~[6]. Therefore in this paper one ofthe estimate method for the collection efficiency of the axial flow cyclones is proposed. The applicationto the geometrically similar type of cyclone of the body diameters D_1=30, 50, 69 and 99 mm showedin good agreement with the experimental results of the collection efficiencies which were described indetail in the paper by Ogawa & Sugiyama~[8].
基金supported by the Hundred Talents Program of Chinese Academy of Sciences (No. 29O827631)
文摘During the 2012 Lanzhou International Marathon, the local government made a significant effort to improve traffic conditions and air quality by implementing traffic restriction measures. To evaluate the direct effect of these measures on urban air quality, especially particle concentrations and their size distributions, atmospheric particle size distributions （0.5-20μm） obtained using an aerodynamic particle sizer （model 3321, TSI, USA） in June 2012 were analyzed. It was found that the particle number, surface area and volume concentrations for size range 0.5-10 μm were （15.0±2.1） cm-3, （11.8±2.6） μm2/cm3 and （1.9±0.6） μm2/cm3, respectively, on the traffic-restricted day （Sunday）, which is 63.2%, 53.0% and 47.2% lower than those on a normal Sunday. For number and surface area concentrations, the most affected size range was 0.5-0.7 and 0.5-0.8 μm, respectively, while for volume concentration, the most affected size ranges were 0.5-0.8, 1.7-2.0 and 5.0-5.4 μm. Number and volume concentrations of particles in size range 0.5-1.0μm correlated well with the number of non-CNG （Compressed Natural Gas） powered vehicles, while their correlation with the number of CNG-powered vehicles was very low, suggesting that reasonable urban traffic controls along with vehicle technology improvements could play an important role in improving urban air quality.
文摘The seasonal transport of the Saharan dust to the West African region, near the Gulf of Guinea, during northem winter has been studied over 12 years. Using an optical particle counter, the dust aerosols in the diameter range 0.5-25 μm have been sampled at Kumasi （6040＇ N, l°34＇ W） in Ghana during the winter months of January-February from 1997 to 2009. The settling atmospheric dust particles observed during the peak Harmattan and the background Harmattan periods are analysed for the mean particle size, number and mass concentrations as well as the particle size-frequency. It is shown that the average daily particle diameter, number and mass concentrations obtained in the peak Harmattan periods are 1.57 ± 0.54 μm, 50 ± 25 particles/cm3 and 1,130 ± 994 μg/m3, respectively, while for the background Harmattan these values are correspondingly, 1.31 ±0.31 μm, 32 ±12 particles/cm3 and 576 ±429 μg/m3, respectively. These experimental results will be useful for the design of ambient air-filters and for understanding the West African climate change.
基金sponsored by National Key Development Program for Fundamental Research (973 Program) Project(Nos.2006CB403703 and 2006CB403701)
文摘Particle size distribution of 12-500 nm was measured at Mt. Waliguan, China Global Atmosphere Watch Baseline Observatory, from Aug. in 2005 to May in 2007.72-hr back-trajectories at 100-m arrival height above ground level for the same period were calculated at 6：00, 12：00, and 21：00 （Beijing Time） for each day using the Hybrid Single-Particle Lagrangian Integrated Trajectory （HYSPLIT-4） model developed by NOAA/ARL. It was found that air mass sources significantly impact particle number concentration and size distribution at Mt. Waliguan. Cluster analysis of back-trajectories show that higher Aitken mode particle number concentration was observed when air masses came from or passed by the northeastern section of Mt. Waliguan, with short trajectory length. High number concentration of nucleation mode was associated with air masses from clean regions, with long trajectory length.
文摘The TSI-3321 APS was used to measure concentration of atmospheric particulates in Ranjiaba region of Yubei District in Chongqing City during March 21- 29,2014,and the temporal variations in the hourly average mass and number concentration and median particle diameter of PM10 and PM2.5 as well as their correlation with relative humidity were analyzed. The results showed that the three indicators of PM10 and PM2.5 except for the mass concentration correlated with relative humidity,of which the correlation between the mass median particle diameter and relative humidity was the best. The correlation coefficient R^2 between the mass median particle diameter of PM10（ PM2.5） and relative humidity was up to 0. 943（ 0. 832）. Therefore,relative humidity and pressure are key impact factors of indicators of particles.
基金supported by the National Natural Science Foundation of China (10872203)the National Basic Research Program(2007AC744701)the CAS Research and Development Program of China (KSCX2-YW-H18)
文摘Direct measurement of slip length is based on the measured fluid velocity near solid boundary. However, previous micro particle image velocimetry/particle tracking velocimetry （microPIV/PTV） measurements have reported surprisingly large measured near-wall velocities of pressure-driven flow in apparent contradiction with the no-slip hy-pothesis and experimental results from other techniques. To better interpret the measured results of the microPIV/PTV, we performed velocity profile measurements near a hy-drophilic wall （z = 0.25-1.5 μm） with two sizes of tracer particles （φ 50 nm and φ200 nm）. The experimental results indicate that, at less than 1 μm from the wall, the deviations between the measured velocities and no-slip theoretical values obviously decrease from 93% of φ200 nm particles to 48% of φ50 nm particles. The Boltzmann-like exponential measured particle concentrations near wall were found. Based on the non linear Boltzmann distribution of particle concentration and the effective focus plane thickness, we illustrated the reason of the apparent velocity increase near wall and proposed a method to correct the measured velocity profile. By this method, the deviations between the corrected measured velocities and the no-slip theoretical velocity decrease from 45.8% to 10%, and the measured slip length on hy-drophilic glass is revised from 75 nm to 16 nm. These results indicated that the particle size and the biased particle concentration distribution can significantly affect near wall velocity measurement via microPIV/PTV, and result in larger measured velocity and slip length close to wall.
基金Project supported by the Major Program of the National Natural Science Foundation of China(No.91852102)。
文摘The Reynolds-averaged general dynamic equation(RAGDE)for the nanoparticle size distribution function is derived,including the contribution to particle coagulation resulting from the fluctuating concentration.The equation together with that of a turbulent gas flow is solved numerically in the turbulent flow of a ventilation chamber with a jet on the wall based on the proposed model relating the fluctuating coagulation to the gradient of mean concentration.Some results are compared with the experimental data.The results show that the proposed model relating the fluctuating coagulation to the gradient of mean concentration is reasonable,and it is necessary to consider the contribution to coagulation resulting from the fluctuating concentration in such a flow.The changes of the particle number concentration M_(0) and the geometric mean diameter dg are more obvious in the core area of the jet,but less obvious in other areas.With the increase in the initial particle number concentration m00,the values of M_(0) and the standard deviation of the particle sizeσdecrease,but the value of d_(g) increases.The decrease in the initial particle diameter leads to the reduction of M_(0) andσand the increase in d_(g).With the increase in the Reynolds number,particles have few chances of collision,and hence the coagulation rate is reduced,leading to the increase in M_(0) andσand the decrease in d_(g).
文摘During the Austral summer of 1996/1997, the First Chinese Antarctic Inland Expedition reached the inland area about 330 km along the direction around 76°E from Zhongshan Station, and collected 84 surface snow samples at an interval of 4 km . Micro particle analysis of the samples indicates that the micro particle concentration apparently decreases with the increasing of altitude, and the amplitudes of micro particle concentration is much larger in the lower altitude than in the higher altitude. Further analysis of grain size distributions of micro particle, percentage of micro particles from different sources and variations with altitude suggest that micro particles in this area are from a considerably dominant source. Although this area is controlled by polar easterly wind and katabatic wind, transportation and deposition of the micro particles are mainly influenced by marine transportation in coastal area.
基金financially supported by the National Key Research and Development Program of China(2016YFC0801700)the Project of the National Natural Science Foundation of China(51604018)the Basic Research Funding of the China Academy of Safety Science and Technology(2019JBKY11 and 2019JBKY04)。
文摘The cyclone separator is an important separation device.This paper presents a new type of embedded two-stage cyclone,which includes a 2 nd-stage cyclone(internal traditional cyclone)with multiple inlets and a 1 st-stage cyclone(outer cylinder)that unifies the 2 nd-stage cyclone inlets into one inlet.The Taguchi experimental method was used to study the two-stage cyclone separator’s inlet area on its performance.Studies have shown that the increase of the 1 st-stage cyclone inlet area and the increase in the number of 2 nd-stage cyclone inlets(N)positively affect reducing the pressure drop and a negative effect on efficiency.It is recommended to use 2 S(the original 1 st-stage cyclone inlet area)of the 1 st-stage cyclone inlet area and 2 N of the 2 nd-stage cyclone inlets when separating fine particles.Compared with a traditional cyclone,the pressure drop is reduced by 1303 Pa,the mass separation efficiency(Eq)is increased by 0.56%,and the number separation efficiency(En)is increased by 2.05%.When separating larger particles,it is recommended to use 2 S of the 1 st-stage cyclone inlet area and 4 N of the 2 nd-stage cyclone inlets.Compared with a traditional cyclone,although Endecreases slightly,the pressure drop is reduced by 3055 Pa,and the Eqis increased by 0.56%.The research results provide new insight into the design of the cyclone.
文摘Based on the analysis of spectrum characteristics of intensity fluctuations while light beams pass through stack gas flow in an industrial setting, this paper puts emphasis upon discussing the spectrum of optical intensity fluctuations by the variety of particle concentration in stack gas flow. This paper also gives the primary theoretical explanation of the measurement results in the stack of coal-fired utility boilers. Meanwhile, the cross-correlation formula is given as the theoretical basis of velocity measurement by using particle concentration scintillation.
基金Funded by the National Natural Science Foundation of China(52004284)the Fundamental Research Funds from the Central University of the Ministry of Education of China(2020QN55)the China Postdoctoral Science Foundation(2019M661979)。
文摘In order to solve the problem that the vulcanizing agent utilization rate is low and the dilution effect of copper slag is poor,the vortex stirring dilution method was used to improve the conditions of the dilution kinetics and copper recovery.The water model was used to simulate the effect of copper slag dilution.Under the premise of keeping the Reynolds number consistent,silicone oil and glass beads were used instead of copper slag and vulcanizing agent.Based on the relationship between voltage and concentration,the PC6D dual-channel particle concentration measuring instrument was used to study the stirring speed and the insertion depth of the stirring paddle in model experiments,and the suitable conditions were speed 250 rpm and insertion depth 70 mm.The fire dilution of copper slag was done under the conditions.After stirring and sedimentation,the Fe_(3)O_(4) in slag decreased from 22.58% to 4.65%,and the copper content of the slag decreased from 2.94% to 0.34%.The copper recovery was 88.44%.
基金Supported by Science Foundation of Tianjin Higher Educational Committee (No. 20031109).
文摘Indoor environment separated with down-feed air curtain was numerically simulated and experimen-tally researched. Indoor airflow and temperature fields separated with air curtain were numerically simulated. Re-sults show that both polluted airflow and thermal air current can be separated with a down-feed air curtain to pre-vent contaminants from spreading in the room space. In a test chamber, the smoke of burning Tibetan incense served as the source of contaminants, and the probe test shows that 1.0 μm is the prevailing diameter of the smoke particles. During the release of the smoke, the particle concentration of the indoor air was tested with a laser particle counter at the points of three different heights from the floor when the air curtain was running or not. Experimental results show that the higher the test point is located, the lower the particle concentration is, implying that the sepa-rating or isolating effect decreases as the air velocity of the curtain reduces along with the height descends. Accord-ing to both simulation and experimental results, down-feed air curtain can separate indoor environment effectively when the supply air velocity of air curtain is not less than 3 m/s. In order to strengthen separation effect, it is sug-gested that the supply air velocity be speeded up to 5 m/s.
基金Funded by Beijing Higher Education Young Elite Teacher Project(No.YETP0371)National Key Technologies R&D Program of China(No.2012BAJ02B02)
文摘The paper presents a simple model for outdoor air contaminant transmission into occupied rooms. In the model, several factors such as filtration, ventilation, deposition, re-emission, outdoor concentration and indoor sources are included. The model results show that the air exchange rate plays an important role in the transmission of outdoor contaminants into the indoor environment. The model shows that increasing the value of the filtration efficiency decreases the mass concentration of indoor particles. In addition, if outdoor aerosol particles have a periodic behaviour, indoor aerosol particles also behave periodically but smoother. Indoor sources are found to be able to increase indoor concentrations greatly and continuously.
文摘An approach is developed to examine the mean and uncertainty of thermal conductivity of a heterogeneous multiparticle system,where the particle concentration or void fraction is treated as a truncated fractal distribution.The truncated fractal distribution is then integrated into the Maxwell model,which is equivalent to a cell model in which the multiparticle system is conceptualized as a spherical fluid cell that envelopes a solid particle.The developed mean thermal conductivity is compared with four experimental data sets of liquid-saturated media from the literature.The effect of fractal characteristics is quantified and discussed.Incorporating particle concentration or void fraction truncated fractal distribution can better capture scatters in the experimental results.The thermal conductivity and its standard deviation decrease with increasing fractal dimensions.When the void fraction is truncated fractal,the uncertainty increases mostly in the low mean void fraction range and drops more quickly with the increasing mean void fraction compared to the case where the particle concentration is truncated fractal.In a typical case of multiparticle system when the solid particles are more conductive than the fluid,the faster increase rate of standard deviation with the ratio of solid over fluid conductivities occurs when the mean void fraction is smaller.
基金This work was supported by the National Natural Science Foundation of China （Grant No. 50578034, Grant No. 40475047）Shanghai Educational Development Foundation Titled ＂Shuguang Project＂, P.R. China （Grant No. 03SG30）.
文摘The time series of indoor and outdoor particle number concentrations in a naturally ventilated residential building in Xi＇an were tested simultaneously for 7 days in summer. The relationships between indoor and outdoor concentrations were examined and discussed, and linear regression analysis was employed to correlate the indoor and outdoor concentrations. The diurnal cycles of indoor and outdoor particle concentrations of different particle size ranges all showed positive correlations between indoor and outdoor number concentrations, The I/O ratios of number concentrations varied with the increase of particle size in the range of 0.89 （±0.19） to 0.99 （±0.15）.
基金the Doctor Creation Foundation of Nanjing University of Science and Technology
文摘A model for measuring aerosol mass concentration by an optical particle counter is presented using the conception of the average mass. In this model, to understand the meaning of the pulse height distribution of particles which is used to inverse mass concentration, the relationship among intensity distribution in the optical sensing volume, particle shape, and the pulse height distribution is discussed. To solve the instability of the equivalent factor, a novel two-step calibration method is proposed. The experimental results demonstrate that mass concentrations calculated by the model are in good agreement with those measured by a norm-referenced instrument. For samples of soot and air, the slopes of fitting lines of data points are 0.9582 and 0.9220, and the correlation coefficients are 0.9991 and 0.9965, respectively.
基金supported by the Program for Postgraduates Research Innovation in University of Jiangsu Province of China (No.CXLX13_955)the National Natural Science Foundation of China (No.51104153)
文摘In order to reveal the influence of forced ventilation on the dispersion of droplets ejected from roadheader-mounted external sprayer,the paper studies the air-flowing field and the droplet distribution under the condition of gentle breeze and normal forced ventilation in heading face using the particle tracking technology of computational fluid dynamics(CFD).The results show that air-flowing tendency in the same section presents great comparability in the period of gentle breeze and forced ventilation,and the difference mainly embodies in the different wind velocity.The influence of ventilation on the dispersion of droplets is faint under the gentle breeze condition.The droplet can be evenly distributed around the cutting head.However,under the normal forced ventilation,a large number of droplets will drift to the return air side.At the same time,droplet clusters are predominantly presented in the lower part of windward side and the middle of the leeward side around the cutting head.In contrast,the droplet concentration in other parts around cutting head decreases a lot and the droplets are unable to form close-grained mist curtain.So the dust escape channel is formed.In addition,the simulation results also reveal that the disturbance of air flow on the droplet distribution can be effectively relieved when using ventilation duct with Coanda effect(VDCE).Field experiment results show that the dust suppression efficiency of total dust and respirable dust increases respectively by 10.5%and 9.3%when using VDCE,which proves that it can weaken the influence of airflow on droplet dispersion.
