• Journal of the Korean Wood Science and Technology
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• 제42권2호
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• pp.119-129
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• 2014

This work undertook to prepare nanofibers of cellulose nanofibrils (CNF)/polyvinyl alcohol (PVA) composite by electrospinning, and characterize the electrospun composite nanofibers. Different contents of CNFs isolated from hardwood bleached kraft pulp (HW-BKP) by 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO)-mediated oxidation were suspended in aqueous polyvinyl alcohol (PVA) solution, and then electrospun into CNF/PVA composite nanofibers. The morphology and dimension of CNFs were characterized by transmission electron microscopy (TEM), which revealed that CNFs were fibrillated form with the diameter of about $7.07{\pm}0.99$ nm. Morphology of the electrospun nanofiber observed by field-emission scanning electron microscopy (FE-SEM) showed that uniform CNF/PVA composite nanofibers were manufactured at 1~3% CNF contents while many beads were observed at 5% CNF level. Both the viscosity of CNF/PVA solution and diameter of the electrospun nanofiber decreased with an increase in CNF content. The diameter and its distribution of the electrospun nanofibers helped explain the differences observed in their morphology. These results show that the electrospinning method was successful in preparing uniform CNF/PVA nanofibers, indicating a great potential for manufacturing consistent and reliable cellulose-based nanofibrils for scaffolds in future applications.

• 한국분말재료학회지
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• 제28권2호
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• pp.120-126
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• 2021

In this study, AlSi10Mg alloy powders are synthesized using gas atomization and sieving processes for powder bed fusion (PBF) additive manufacturing. The effect of nozzle diameter (ø = 4.0, 4.5, 5.0 and 8.0 mm) on the gas atomization and sieving size on the properties of the prepared powder are investigated. As the nozzle diameter decreases, the size of the manufactured powder decreases, and the uniformity of the particle size distribution improves. Therefore, the ø 4.0 mm nozzle diameter yields powder with superior properties. Spherically shaped powders can be prepared at a scale suitable for the PBF process with a particle size distribution of 10-45 ㎛. The Hausner ratio value of the powder is measured to be 1.24. In addition, the yield fraction of the powder prepared in this study is 26.6%, which is higher than the previously reported value of 10-15%. These results indicate that the nozzle diameter and the post-sieve process simultaneously influence the shape of the prepared powder as well as the satellite powder on its surface.

• 한국산림과학회지
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• 제97권5호
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• pp.485-491
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• 2008

This study was performed in 14 unthinned Mongolian pine (Pinus sylvestris L. var. mongolica Litvin) plantations in northeast China. Data were collected on 70 sample trees of different canopy position with diameter at breast height (DBH) ranging from 6.9 cm to 34.5 cm. Diameter and length of knots per whorl below the living crown were studied by different vertical levels divided by relative knot height (RHK) in this paper. Models taking DBH and height to the crown base (HCB) as independent variables were developed to predict knot diameter (KD) in a sample whorl. According to the vertical distribution tendency and range of sound knot length (KLsound), KLsound was modeled as multiple linear function of DBH, KD and relative knot height (RHK). The loose knot length (KLloose) was described as a function of DBH, KD and height above the ground for knots (HK) in a mixed log-linear model. Results from this study can provide abundant knot information so as to describe the knot size and vertical distribution tendency of Mongolian pine plantation.

• 한국재료학회지
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• 제23권12호
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• pp.737-744
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• 2013

We demonstrated size control of Au nanoparticles by heat treatment and their use as a catalyst for single-walled carbon nanotube (SWNTs) growth with narrow size distribution. We used uniformly sized Au nanoparticles from commercial Au colloid, and intentionally decreased their size through heat treatment at 800 oC under atmospheric Ar ambient. ST-cut quartz wafers were used as growth substrates to achieve parallel alignment of the SWNTs and to investigate the size relationship between Au nanoparticles and SWNTs. After the SWNTs were grown via chemical vapor deposition using methane gas, it was found that a high degree of horizontal alignment can be obtained when the particle density is low enough to produce individual SWNTs. The diameter of the Au nanoparticles gradually decreased from 3.8 to 2.9 nm, and the mean diameter of the SWNTs also changed from 1.6 to 1.2 nm for without and 60 min heat treatment, respectively. Raman results reconfirmed that the prolonged heat treatment of nanoparticles yields thinner tubes with narrower size distribution. This work demonstrated that heat treatment can be a straightforward and reliable method to control the size of catalytic nanoparticles and SWNT diameter.

• 대한기계학회논문집B
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• 제25권11호
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• pp.1492-1499
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• 2001

In order to develop the compact and flexible heat exchangers, we made the helically coiled heat exchangers. They can be manufactured with small diameter copper tubes without the need for fins; inner diameter=1.0 mm, straight tube length=1.5 m. The experiments were carried out with the following conditions; evaporation pressure=0.6 MPa, air velocity=0.7 ∼ 1.7 m/s, and working fluid=R-22. Pressure drop and heat transfer coefficient of heat exchangers were experimented according to the air velocity. The results of heat transfer coefficient show a 35% beneficial increase fur these heat exchangers over the other covered fin-tube heat exchangers. A cooling capacity of about 3 kW was obtained with an air velocity of 1.5 m/s. The distribution header has also been designed fur efficient distribution of refrigerant flow.

• Bulletin of the Korean Chemical Society
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• 제20권10호
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• pp.1209-1212
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• 1999

The entropies and chemical potentials of hard-sphere solutes solvated in hard-sphere solids were calculated by Monte Carlo method using the radial free-space distribution function. This method is based on calculating the entropy by comparing the free volume of a molecule with that of an ideal gas, and is applicable even when the size of solute is very large and the solvent is a solid. When the diameter of hard-sphere solute is small the solute molecule behaves as like as a fluid in solid structures, but when the diameter of solute becomes large, a fluid-to-solid phase transition takes place. The fluid-to-solid phase transition occurs at the region of the smaller size of solute with the more increase of solvent density. The least square fit values of analytical form of the radial free-space distribution functions of solute molecules are presented for future uses.

• Archives of Pharmacal Research
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• 제12권3호
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• pp.214-218
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• 1989

Atmospheric particulate matters (A. P. M. ) were collected on quartz-fiber filters from March 1985 to May 1986, using the Andersen high-volume air sampler and contents of six heavy metals (Fe, Mn, Cu, Zn, Pb Ni) in the A. P. M. were determined by atomic absorption spectrophotometry. These heavy metals were divided into the three groups with respect to their particle size distribution. Fe and Mn were mainly associated with coarse particles (diameter > 2.0 $\mu$m), but Pb and Ni were related fine particles (diameter < 2.0 $\mu$m). Cu and Zn had mized size distributions in both of them. In the seasonal variation of heavy metals, the contents of Fe and Mn in spring and Ni and Pb in winter were higher than any other season. There were high mutual correlation between Fe and Mn coarse particles, and between Pb and Ni in fine particles.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2006년 창립20주년기념 정기학술대회 및 국제워크샵
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• pp.441-444
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• 2006

Nakdong river estuary is located at south-eastern coast if the Korea. Especially, Complicating topography change is generated by interaction of much sediment, wave and tide. This study is investigated into observation data of grading size distribution in the post and surface sediment characteristics is investigated into grading size analysis using sieve analysis in Nakong river estuary. As a result, mean diameter of surface sediment is distributed to front of shoal as a size with 0.1~0.2 mm and mean diameter of the last generated shoal is about 0.2~0.3 mm.

• 한국정밀공학회지
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• 제23권9호
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• pp.127-133
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• 2006

Cold expansion method is used to protect a fatigue fracture from fastener hole in the structure and aerospace industry. Cold expansion is that an oversized tapered mandrel goes through the hole and produces a compressive residual stress as well as plastic deformation around the hole. Here, mandrel shapes are one of the factors which are influenced on the residual stress distribution by cold expansion method. This paper, according to mandrel shapes (diameter of mandrel, length of mandrel and length of taper), we are performed a finite element analysis of residual stress distribution by cold expansion method. From this study, it has been found that diameter of mandrel and length of taper are an important factor which was generated a low compressive residual stress surround of fastener hole by cold expansion method.

• 대한설비공학회지:설비저널
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• 제16권4호
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• pp.383-391
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• 1987

An experimental investigation has been conducted to determine the flow pattern for two-component , two-phase mixtures which flow vertically upwards in concentric annuli based on the measurement for the local void fraction and the distribution of the local void fraction in various radial locations in the annular gap. The annular test section consists of a lucite outer tube whose inside diameter is 38mm and a stainless steel rod, The rod diameter is either :2mm,16mm or 20mm. It is demonstrated that the probability density function of the fluctuations in void fraction may be used as an flow pattern indicator and the local void fraction distribution depends on the flow pattern and radial location in the annular passage.