• 폴리머
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• 제38권4호
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• pp.449-456
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• 2014

Ternary blends of poly(L-lactic acid) (PLLA), poly(${\varepsilon}$-caprolactone) (PCL) and polyethylene oxide (PEO) were produced with different concentrations of components via melt blending. By leaching the PEO from the samples by water, porous materials were obtained with potential application for bio scaffolds. Sample porosity was evaluated by calculating the ratio of porous scaffold density (${\rho}^*$) to the non-porous material density (${\rho}_s$). Highest porosity (51.42%) was related to the samples containing 50 wt%. of PEO. Scanning electron microscopy (SEM) studies showed the best porosity resulted by decreasing PLLA/PCL ratio at constant concentration of PEO. Crystallization behavior of the ternary blend samples was studied using differential scanning calorimetry (DSC). Results revealed that the crystallinity of PLLA was improved by addition of PEO and PCL to the samples. The porosity plays a key role in governing the compression properties. Mechanical properties are presented by Gibson-Ashby model.

• 대한기계학회논문집B
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• 제20권10호
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• pp.3243-3250
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• 1996

Emission characteristics of nitric oxides and carbon monoxide from a porous media combustor has been experiment studied. The relationship between the change of flame shape and emission has also been examined. As the equivalence ratio decreases, the flame shape on the ceramic matrix plate changes from a diffusion flame, R(radiant)-type flame, to B(Blue)-type flame. With large fuel flow rate, R-type flame turns to be two dimensional R-II type flame around the equivalence of 0.7. Carbon monoxide emission increases very rapid with decreasing equivalence ratio. It changes a lot from some 10 ppm to 100-10,000 ppm with the change of flame type from R-I to R-II type. Nitric oxide emission from the premixed burner is less than 25 ppm over all range of fuel flow rate, which is less than 20% of NOx emission from conventional gas burners.

• 대한기계학회논문집B
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• 제24권8호
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• pp.1119-1127
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• 2000

Convective heat transfer in a channel filled with porous media has been analyzed in this paper. The two-equation model is applied for the heat transfer analysis with the velocity profile, considering both the inertia and viscous effects. Based on a theoretical solution, the effect of the velocity profile on the convective heat transfer is investigated in detail. The Nusselt number is obtained in terms of the relevant physical parameters, such as the Biot number for the internal heat exchange, the ratio of effective conductivities between the fluid and solid phases, and hydraulic boundary layer thickness. The results indicate that the influence of the velocity profile is characterized within two regimes according to the two parameters, the Biot number and the conductivity ratio between the phases. The decrease in the heat transfer due to the hydraulic boundary layer thickness is 15% at most within a practical range of the pertinent parameters.

• Advances in concrete construction
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• 제8권4호
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• pp.305-309
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• 2019

Pervious concrete pavements are the need of the day to avoid urban flooding and to facilitate ground water recharge. However, the strength of pervious or porous concrete is considerably less compared to conventional concrete. In this experimental investigation, an effort is made to improve the strength of pervious concrete by adopting fibres and a small amount of fine aggregate. A porous concrete with cement to aggregate ratio of 1:5 and a water-powder ratio of 0.4 is adopted. 30% of the cement is replaced by cementitious material ground granulated blast furnace slag (GGBS) for better strength and workability. Recron fibres at a dosage of 0.5, 1.0 and 1.5% by weight of cement were included to improve the impact strength. Since concrete pavements are subjected to impact loads, the impact strength was also calculated by "Drop ball method" in addition to compressive strength. The effect of fine aggregate and recron fibres on workability, porosity, compressive and impact strength was studied. The investigations have shown that 20% inclusion of fine aggregate and 1.5% recron fibres by weight of cement give better strength with an acceptable range of porosity.

• 공업화학
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• 제7권4호
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• pp.777-786
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• 1996

Seed 중합 방법에 의하여 단분산성 다공의 폴리아크릴로니트릴-에틸렌글리콜 디메타크릴레이트 (PAN) 고분자 마이크로 겔이 제조되었다. PAN 마이크로 겔의 물리적인 특성을 모노머/seed와 희석제/모노머의 비율, 가교제의 농도 및 희석제의 종류에 따라 연구하였다. PAN 마이크로 겔의 입도 분포는 모노머/seed의 비율이 50 이하 일 때 단분산성을 나타냈으며, 가교제의 농도가 증가할수록 입자 내부의 미소 구체 (microsphere)의 크기가 작아져 더욱 밀집된 형태를 나타내기 때문에 입자의 비표면적이 증대되었다. 또한 희석제로 톨루엔을 사용하고 희석제/모노머의 비율이 1.0일 때 입자표면의 세공이 가장 발달되었다.

• Computers and Concrete
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• 제26권1호
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• pp.31-52
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• 2020

This paper investigates the size dependent effect on the vibration analysis of a porous nanocomposite viscoelastic plate reinforced by functionally graded-single walled carbon nanotubes (FG-SWCNTs) by considering nonlocal strain gradient theory. Therefore, using energy method and Hamilton's principle, the equations of motion are derived. In this article, the effects of nonlocal parameter, aspect ratio, strain gradient parameter, volume fraction of carbon nanotubes (CNTs), damping coefficient, porosity coefficient, and temperature change on the natural frequency are perused. The innovation of this paper is to compare the effectiveness of each mentioned parameters individually on the free vibrations of this plate and to represent the appropriate value for each parameter to achieve an ideal nanocomposite plate that minimizes vibration. The results are verified with those referenced in the paper. The results illustrate that the effect of damping coefficient on the increase of natural frequency is significantly higher than the other parameters effect, and the effects of the strain gradient parameter and nonlocal parameter on the natural frequency increase are less than damping coefficient effect, respectively. Furthermore, the results indicate that the natural frequency decreases with a rise in the nonlocal parameter, aspect ratio and temperature change. Also, the natural frequency increases with a rise in the strain gradient parameter and CNTs volume fraction. This study can be used for optimizing the industrial and medical designs, such as automotive industry, aerospace engineering and water purification system, by considering ideal properties for the nanocomposite plate.

• 한국표면공학회지
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• 제53권6호
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• pp.312-321
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• 2020

Morphology of porous cobalt electro-deposits was systematically investigated as functions of cobalt precursors in the plating bath and applied cathodic current density with a special focus on cobalt nano-rod formation. It was proved that the concentration of cobalt precursor plays little effect on the morphology of cobalt electro-deposits at relatively low plating current density while it significantly affects the morphology with increasing plating current density. Such a dependence was discussed in terms of the kinetics of two competitive reactions of cobalt reduction and hydrogen evolution. Cobalt nano-rod structure was created at specific ranges of cobalt precursor content and applied cathodic current density, and its diameter and length varied with plating time without notable formation of side branches which is usually found during dendrite formation. Specifically, the nano-rod length was preferentially increased in relative short plating time (<15 s), resulting in higher aspect ratio of nano-rod with plating time. Whereas, both the nano-rod length and diameter were increased nearly at the same level in a prolonged plating time, making the aspect ratio unchanged. From the analysis of crystal structure, it was confirmed that the cobalt nano-rod preferentially grew in the form of single crystal on a dense poly-crystalline cobalt thin film initially formed on the substrate.

• Journal of applied mathematics & informatics
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• 제7권3호
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• pp.773-785
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• 2000

In this paper an algorithm is presented based on the additive Schwarz method for steady groundwater flow in a porous medium. The subproblems in the algorithm correspond to the problem on a coarse grid and some overlapping subdomains. It will be shown that the rate of convergence is independent of the mesh parameters and discontinuities of the coefficients, and depends on the overlap ratio.

• 한국세라믹학회지
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• 제46권1호
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• pp.16-23
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• 2009

The porous pellets were prepared from porphyry by slurry foaming method. The effect of sintering temperatures on pore structure of porous porphyry pellets with different extension ratio ($E_R$) was investigated by specific surface area, water absorption and porosity, which changed with sintering temperatures. When the sintering temperatures increased from $975^{\circ}C$ to $1075^{\circ}C$, specific surface area and water absorption of the all samples decreased. In case of the sample with an equal sintering temperature, $E_R=3.0$ pellets had little influence on pore structure compared to the $E_R=2.0$ pellets. As a results, it was shown by SEM that facilitated formation of micro pores at $E_R=2.0$ pellets shrunk increasingly after sintering process. At $E_R=3.0$ and sintering temperature at $1025^{\circ}C$, optimum conditions of the porous porphyry porous pellets was found. Also, Escherichia coli removal efficiency of the silver-containing porphoyry porous pellets was measured for the feasibility as a antibacterial media. The antibacterial activity of prepared silver-containing sample was maintained above 90% for 40 days.

• 한국추진공학회지
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• 제7권4호
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• pp.33-38
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• 2003

플룸간섭 현상은 플룸에 의한 경계층 유동의 박리, 강한 전단층의 발생, 그리고 다수의 충격파들이 박리유동 및 전단층과 상호작용하게 되는 매우 복잡한 유동현상으로, 현재 미사일의 후미부에서 발생하는 플룸간섭 현상의 상세에 관해서는 잘 알려져 있지 않다. 본 연구에서는 초음속 미사일의 동체후미부에서 발생하는 플룸간섭 현상의 특징 및 동체기저부에 설치된 다공확장벽(porous extension)의 플룸간섭 현상에 대한 영향을 수치해석적으로 조사하였다. 그 결과, 다공확장벽이 플룸에 의한 충격파와 경계층 유동의 박리를 완화시켜 미사일 동체의 제어성능이 향상될 수 있음을 알았다.