• Journal of Electrical Engineering and Technology
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• v.12 no.5
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• pp.2021-2030
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• 2017

In this paper, the unipolar corona-needle charger was developed and its capabilities were both numerically and experimentally investigated. The experimental corona discharges and particle losses in the charger were obtained at different corona voltage, aerosol flow rate and particle diameter for positive and negative coronas. Inside the charger, the electric field and charge distribution and the transport behavior of the charged particle were predicted by a numerical simulation. The experimental results yielded the highest ion number concentrations of about $1.087{\times}10^{15}ions/m^3$ for a positive corona voltage of about 3.2 kV, and $1.247{\times}10^{16}ions/m^3$ for a negative corona voltage of about 2.9 kV, and the highest $N_it$ product for positive and negative coronas was found to about $7.53{\times}10^{13}$ and $8.65{\times}10^{14}ions/m^3$ s was occurred at the positive and negative corona voltages of about 3.2 and 2.9 kV, respectively, and the flow rate of 0.3 L/min. The highest diffusion loss was found to occur at particles with diameter of 30 nm to be about 62.50 and 19.33 % for the aerosol flow rate of 0.3 and 1.5 L/min, respectively, and the highest electrostatic loss was found to occur at particles with diameters of 75 and 50 nm to be about 86.29 and 72.92 % for positive and negative corona voltages of about 2.9 and 2.5 kV, respectively. The numerical results for the electric field distribution and the charged particles migration inside the charger were used to guide the description of the electric field and the behavior of charged particle trajectories to improve the design and refinement of a unipolar corona-needle charger that otherwise could not be seen from the experimental data.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.3
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• pp.551-560
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• 1988

Gas-particle two phase flow and heat transfer in a cavity receiving thermal radiation through selectively transparent walls have been analyzed by a finite difference method. Particles injected from the upper hole of the cavity are accelerated downward by gravity and exit through the lower hole while they absorb, emit and scatter the incident thermal radiation. Gas phase is heated through convection heat transfer from particles, and consequently buoyancy induced flow field is formed. Two-equation model with two-way coupling is adopted and interaction terms are treated as sources by PSI-Cell method. For the particulate phase, Lagrangian method is employed to describe velocities and temperatures of particles. As thermal radiation is incident upon horizontally, radiative heat transfer in the vertical direction is assumed negligible and two-flux model is used for the solution of radiative heat flus. Gas phase velocity and temperature distributions, and particle trajectories, velocities and temperatures are presented. The effects of particle inlet condition, particle size, injection velocity and particle mass rate are mainly investigated.

• Structural Engineering and Mechanics
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• v.86 no.5
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• pp.607-619
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• 2023

This study, it was tried to evaluate the asphalt behavior under tensile loading conditions through indirect Brazilian and direct tensile tests, experimentally and numerically. This paper is important from two points of view. The first one, a new test method was developed for the determination of the direct tensile strength of asphalt and its difference was obtained from the indirect test method. The second one, the effects of particle size and loading rate have been cleared on the tensile fracture mechanism. The experimental direct tensile strength of the asphalt specimens was measured in the laboratory using the compression-to-tensile load converting (CTLC) device. Some special types of asphalt specimens were prepared in the form of slabs with a central hole. The CTLC device is then equipped with this specimen and placed in the universal testing machine. Then, the direct tensile strength of asphalt specimens with different sizes of ingredients can be measured at different loading rates in the laboratory. The particle flow code (PFC) was used to numerically simulate the direct tensile strength test of asphalt samples. This numerical modeling technique is based on the versatile discrete element method (DEM). Three different particle diameters were chosen and were tested under three different loading rates. The results show that when the loading rate was 0.016 mm/sec, two tensile cracks were initiated from the left and right of the hole and propagated perpendicular to the loading axis till coalescence to the model boundary. When the loading rate was 0.032 mm/sec, two tensile cracks were initiated from the left and right of the hole and propagated perpendicular to the loading axis. The branching occurs in these cracks. This shows that the crack propagation is under quasi-static conditions. When the loading rate was 0.064 mm/sec, mixed tensile and shear cracks were initiated below the loading walls and branching occurred in these cracks. This shows that the crack propagation is under dynamic conditions. The loading rate increases and the tensile strength increases. Because all defects mobilized under a low loading rate and this led to decreasing the tensile strength. The experimental results for the direct tensile strengths of asphalt specimens of different ingredients were in good accordance with their corresponding results approximated by DEM software.

• Proceedings of the Korean Environmental Health Society Conference
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• 2005.06a
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• pp.311-314
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• 2005

To evaluate the acute effects of fine particles on pulmonary function, a longitudinal study was conducted. This study was carried out for the schoolchildren(3rd and 4th grades) living in Inner-Mongolia, China. 113 Chinese children were asked to record their daily levels of peak expiratory flow rate(PEPR) using portable peak flow meter(mini-Wright) for 40 days and 3 time everyday(12 April 2004 to 21 May 2004). The atmospheric concentration of fine particles in study area was also determined everyday during same period. The relationship between dailypeak expiratory flow rate(PEFR) and fine particle levels was analyzed using a mixed linear regression models including gender, age, height, the presence of respiratory symptoms, and daily average relative humidity as extraneous variables. The analysis showed that the increase of fine particle concentrations was negatively associated with the variability in PEPR. The IQR(inter-quartile range) increments of $PM_{10}$ or $PM_{2.5}(66.0{\mu}g/m^3$ and $118.9{\mu}g/m^3$, respectively) were also shown to be related with 1.422L/min(95% Confidence intervals: 0.270 ${\sim}$ 2.574) and 1.214L1min(95% Cl: 0.010 ${\sim}$ 2.418) decline in PEFR.

• Particle and aerosol research
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• v.11 no.4
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• pp.115-118
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• 2015

An electrospray patterning method has been considered as a new and effective way for controlling very fine droplets. Drop-on-demand patterning for unstained nutrient broth on wafers was newly conducted with an electrospray pulsed jet. The patterns had been made under varying experimental conditions including flow rate, vibration frequency, and translational speed of the electrospray patterning system. In this experiment, especially, variation of nutrient broth droplet was measured under varying flow rate conditions. This new technique has a potential to be applied in biology experiments and hormone medical industry.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.4
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• pp.304-311
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• 2006

Experiments on evaporative spray cooling on the square plate heaters with plain or micro-porous coated surfaces were performed in this study. Micro-porous coated surfaces were made by using DOM [Diamond particle, Omegabond 101, Methyl-Ethyl-Keton] method. In case of purely air-jet cooling, the micro-porous coating doesn't affect the cooling capacity. In spray cooling three different flow patterns (complete wetting, evaporative wetting, dryout) are observed on both plain and micro-porous coated surfaces. The effects of various operating conditions, such as water flow rate, particle size, and coating thickness were investigated on the micro-porous coated surfaces. It is found that the level of surface wetting is an important factor to determine the performance of spray cooling. It depends on the balance between absorbed liquid amount by capillary force over porosity and the evaporative amount. The micro-porous coated surface has largest cooling capacity, especially in the evaporative wetting zone. It is found that the effects of liquid flow rate and coating thickness are significant in evaporative wetting zone, but are not in complete wetting and dryout zones.

• Journal of Korea Water Resources Association
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• v.55 no.11
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• pp.955-967
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• 2022

Existing particle tracking models predict vertical displacement of particles based on the terminal settling velocity in the stagnant water. However, experimental results of the present study confirmed that the settling velocity of particles is influenced by the turbulence effects in turbulent flow, consistent with the previous studies. The settling velocity of particles and turbulent characteristics were measured by using PTV and PIV methods, respectively, in order to establish relationship between the particle settling velocity and the ambient turbulence. It was observed that the settling velocity increase rate starts to grow when the particle diameter is of the same order as Kolmogorov length scale. Compared with the previous studies, the present study shows that the graphs of the settling velocity increase rate according to the Stokes number have concave shapes for each particle density. In conclusion, since the settling velocity in the natural flow is faster than in the stagnant water, the existing particle tracking model may estimate a relatively long time for particles to reach the river bed. Therefore, the results of the present study can help improve the performance of particle tracking models.

• Analytical Science and Technology
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• v.34 no.2
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• pp.87-98
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• 2021

In this study, we developed the nanoparticle multi-generator by 3D printer fusion deposition modeling (FDM) method that can reliably generate and deliver nanoparticles at a constant concentration for inhalation risk assessment. A white ABS filament was used as the test material, and SMPS was used for concentration analysis such as particle size and particle distribution. In the case of particle size, the particle size was divided by 100 nm or less and 100 to 1,000 nm, and the number of particles concentration, mass concentration, median diameter of particles, geometric average particle diameter, etc were measured. The occurrence conditions were the extruder temperature, the extruding speed of the nozzle, and the air flow rate, and experiments were conducted according to the change of conditions including the manufacturer's standard conditions. In addition, the utility of inhalation risk assessment was reviewed through a stability maintenance experiment for 6 h. As a result of the experiment, the size of the nanoparticles increased as the discharger temperature increased, as the discharge speed of the nozzle increased, and as the air flow rate decreased. Also, a constant pattern was shown according to the conditions. Even when particles were generated for a long time (6 h), the concentration was kept constant without significant deviation. The distribution of the particles was approximately 80 % for particles of 60 nm to 260 nm, 1.7 % for 1 ㎛ or larger, 0.908 mg/㎥ for the mass concentration, 111 nm for MMAD and 2.10 for GSD. Most of the ABS particles were circular with a size of less than 10 nm, and these circular particles were aggregated to form a cluster of grape with a size of several tens to several hundred nm.

• Korea-Australia Rheology Journal
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• v.17 no.4
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• pp.207-215
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• 2005

We present a finite difference solution for electrokinetic flow in rectangular microchannels encompassing Navier's fluid slip phenomena. The externally applied body force originated from between the nonlinear Poisson-Boltzmann field around the channel wall and the flow-induced electric field is employed in the equation of motion. The basic principle of net current conservation is applied in the ion transport. The effects of the slip length and the long-range repulsion upon the velocity profile are examined in conjunction with the friction factor. It is evident that the fluid slip counteracts the effect by the electric double layer and induces a larger flow rate. Particle streak imaging by fluorescent microscope and the data processing method developed ourselves are applied to straight channel designed to allow for flow visualization of dilute latex colloids underlying the condition of simple fluid. The reliability of the velocity profile determined by the flow imaging is justified by comparing with the finite difference solution. We recognized the behavior of fluid slip in velocity profiles at the hydrophobic surface of polydimethylsiloxane wall, from which the slip length was evaluated for different conditions.

• Journal of the Korean Ceramic Society
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• v.30 no.1
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• pp.25-33
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• 1993

Formation reaction of Mn-Zn ferrite depending on various synthetic conditions of wet process was investigated using FeCl2.nH2O(n≒4), MnCl2.4H2O, ZnCl2 as starting materials. A stable intermediate precipitate was formed by the addition of H2O2. And the precipitate was hard to transform to spinel phase of Mn-Zn Fe2O4. Single phase of Mn-Zn Fe2O4 spinel was obtained above 8$0^{\circ}C$ reaction temperature. The powder had spherical particle shape and 0.02~0.05${\mu}{\textrm}{m}$ particle size. Fe(OH)2 solid solution, -FeO(OH) solid solution, -FeOOH, Mn-Zn Fe2O4 spinel were formed with air flow rate 180$\ell$/hr. However, single phase of Mn-Zn Fe2O4 spinel with cubic particle shape and 0.1~0.2${\mu}{\textrm}{m}$ particle size was formed with synthetic conditions of 8$0^{\circ}C$ and 90 munutes. The particle shape of the -FeOOH was needle-like.