• 한국산학기술학회논문지
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• 제22권3호
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• pp.611-619
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• 2021

다공성 아스팔트 포장은 혼합물 속에 포함된 20%정도의 공극으로 인해 도로의 수막현상을 억제하여 교통사고를 줄이고 교통소음을 획기적으로 줄이는 등 다양한 순기능을 갖는다. 그러나 다공성 아스팔트 혼합물은 혼합물 속에 포함된 20% 정도의 공극 때문에 혼합물의 내구성이 취약하게 되며, 이러한 취약한 내구성이 다공성 포장의 적용을 확장하는데 제약요인이 되고 있다. 본 연구의 목적은 다공성 포장의 내구성을 향상시키기 위해 최대입경, 온도 그리고 공극률의 변화가 혼합물의 균열저항성 및 수분민감성 등 혼합물의 내구성에 미치는 영향을 평가하는 것이다. 다공성 아스팔트 혼합물의 내구성을 평가하기 위해 간접인장강도를 균열저항성 및 수분민감성의 척도로 설정하였다. 공극률이 20%로 동일하고 최대입경이 13mm, 10mm, 8mm인 혼합물에 대하여 상온과 동결융해를 경험한 시료에 대하여 간접인장강도 시험을 실시하였다. 그리고 최대입경 10mm인 동일한 재료로 공극이 20%와 22%인 혼합물에 대하여 동일한 시험을 실시하였다. 실험결과 공극률은 20%로 동일하고 최대입경의 변화와 온도의 변화에 유의한 차이를 보이는 것으로 나타났다. 특히 실험온도에 대해서는 상온과 저온에서 유의한 차이를 보였다. 최대입경의 변화에 대해서는 상온에서 8mm보다 13mm가 분명히 높은 강도를 보이고 저온에서는 유의한 차이를 보이지 않았다. 그리고 공극률과 온도의 변화에 대한 실험에서는 온도에 대해서는 유의한 차이를 보였지만 20%와 22% 사이의 2% 공극 차이는 내구성에 유의한 차이를 보이지 못했으며 서로간의 교호작용도 없는 것으로 나타났다. 앞으로 다공성 아스팔트 혼합물의 내구성에 미치는 요소들의 정량적인 평가를 통해 보다 내구성 있는 다공성 아스팔트포장을 개발해 나갈 필요가 있다.

• 대한토목학회논문집
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• 제30권1A호
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• pp.53-59
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• 2010

최근 들어 적외선을 이용하여 콘크리트 구조물의 결함 또는 공동 등을 평가하려는 비파괴 연구가 활발하게 진행되고 있으며, 이는 유지관리기법의 중요한 부분을 이루고 있다. 적외선 화상분석(Infrared Thermography)을 콘크리트 표면에 적용할 경우, 콘크리트의 표면온도는 표면을 구성하는 재질과 열적특성(비열, 열전도율, 열전달율)에 따라 그 응답이 다르게 나타나게 된다. 서로 다른 배합을 가지는 시멘트 모르타르에서는 공극률이 다르게 구성되고, 표면에서 공극률의 차이는 열에 노출된 뒤, 냉각되는 과정에서 열적 거동이 다르게 평가된다. 한편 이러한 공극률은 강도 및 염화물 확산계수와 같은 역학적/내구적 특성에 영향을 주기도 한다. 본 연구에서는 외부에서 열을 가하여 측정하는 능동방식(active type)을 이용하여, 표면의 온도변화를 분석하였다. 물-시멘트비 55%와 65%인 시멘트 모르타르 시편을 제작하였으며, 공극률, 압축강도, 염화물 확산계수 등의 물리적 특성값들이 평가되었다. 이후 동일한 실내조건(온도 $20{\sim}22^{\circ}C$, 습도 55-60%)에서 적외선 화상분석 기법을 적용하였다. 시간의 경과에 따라 공극을 많이 포함하는 시편의 경우, 표면 온도가 상대적으로 증가하였으며, 온도가 일정해지는 시점(임계시점)이 단축되고 있음을 확인할 수 있었다. 이러한 특성은 콘크리트와 같이 공극과 골재를 가지고 있는 복합재료의 품질 평가에 적용할 수 있음을 시사한다. 한편 공극률과 실험상수를 고려하여, 공극률에 따라 변화하는 임계시간에 대한 계산식을 제안하였다. 본 논문에서는 시멘트 모르타르의 공극량의 변화에 따른 물리적 변화와 이에 따른 열특성 변화가 논의될 것이다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 D
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• pp.1547-1549
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• 1999

As a preliminary experiment for the development of anode-supported tubular cell with proper porosity, we have investigated the anode substrate and the electrolyte-coated anode tube. The anode substrate was manufactured as a function of carbon content in the range of 20 to 50 vol.%. As the caron content increased, the porosity of the anode substrate increased slightly and the carbon content with proper porosity was obtained at 30 vol.%. The anode tube was fabricated by extrusion process and the electrolyte layer was coated on the anode tube by slurry dipping process. The anode-supported tube was cofired successfully. Their sintered property and microstructure were examined and the porosity of the anode tube was 35%. From the gas permeation test, the anode tube was found to be porous enough for gas supply. On the other hand, the anode-supported tube with electrolyte layer indicated a very low gas permeation rate. This means that the coated electrolyte was dense. Based upon these experimental results. we will fabricate and test the anode-supported tubular cell.

• 한국세라믹학회지
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• 제53권1호
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• pp.13-17
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• 2016

It is highlighted that increasing the adsorbent surface area on volumetric basis is very important in providing an easy access for gas molecules. Fine particles around $3{\mu}m$ of soft-burned dolomite kiln dust (SB-DKD) were hydrated to wet slurry samples by ball mill process and then placed in a chamber to use spray dryer method. Spherical granules with particle size distribution of $50{\sim}60{\mu}m$ were prepared under the experimental condition with or without addition of a pore-forming agent. The relationship between bead size of the pore-forming agent and size of SB-DKD particles is the most significant factor in preparation of spherical granules with a high porosity. Whereas addition of smaller beads than SB-DKD resulted in almost no change in the surface porosity of spherical granules, addition of larger beads than SB-DKD contributed to obtaining of the particles with both 15 times larger average pore volume and 1 order of magnitude larger porosity. It is considered that spherical granules with improved $N_2$ gas adsorption ability may also be utilized for other atmospheric gas adsorption.

• 한국세라믹학회지
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• 제53권1호
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• pp.34-42
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• 2016

Characteristics of wet flue gas desulfurization and in-furnace desulfurization of domestic and overseas limestone with different crystallinity and crystalline size are studied in this article. Properties of desulfurization were evaluated in relation to physicochemical/ mineralogical characteristics, degree of pore formation for different calcination temperatures and TNC(total neutralizing capability). TNC of domestic high crystalline limestone was lower than that of overseas one. On the other hand, the porosity after calcination was shown to be relatively high for domestic limestone, which had high initial rates of desulfurization reactions in-furnace. Based on low pore formation and porosity with high TNC of crystalline high-Ca limestones compared to macrocrystalline ones, the former are preferred for wet desulfurization processes.

• 대한기계학회논문집B
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• 제20권8호
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• pp.2670-2680
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• 1996

Effeccs of porous wind fence on surface-pressure around 2-dimensional prism model of triangular cross-section were investigated experimentally. The pressure data were obtained at a Reynolds number based on the model height of Re=2.1*10$^{5}$ . Flow visualization also carried out to investigate the flow structure qualitatively. The mean velocity and turbulent intensity profiles measured at fence location were well fitted to the neutral atmospheric surface boundary layer over the open terrain. Various fences with different porosity and height were tested to investigate their effects on the surface pressure acting on a prism model at different locations. As the results, porous fence with porosity 40 ~ 50% is most effective for abating wind erosion. With decreasing porosity of the fence, pressure fluctuations on the model surface are increased. The mean pressure coefficients are decreased only when the fence height is greater than the model height. The effect of distance between wind fence and triangular prism was not significant, compared to that of the fence porosity and height.

• Journal of Advanced Marine Engineering and Technology
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• 제26권4호
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• pp.464-471
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• 2002

Porosity formation in partial penetration welds by high power lasers is a serious problem in industry. There are two main causes that induce porosity formation. One form of porosity is due to gases (e.g. hydrogen, oxygen) dissolving into the weld pool because of the high temperature and then the rapid solidification traps gases as a bubble in the weld metal. The second problem is voids formed by the keyhole collapsing due to unstable keyhole fluid dynamics. The voids that form at the bottom of the keyhole are relatively large and irregular in shape compared to the gas bubbles; this void formation is the primary concern in this paper. The reduction of voids formed by keyhole collapse is achieved by improving the stability of keyhole. Two methods to improve keyhole stability are discussed in this paper: pulse modulation and beam incident angle. Pulse modulation of the laser beam was performed between 100 Hz and 500 Hz to find out the optimum frequency for the keyhole dynamics. The incident beam angle changed the impact angle of the laser beam to the work surface in a range of 0 to 25 degrees. Glycerin in a semi-solidified state is used as a medium for performing the welding because its transparency allows of visualization of the keyhole.

• 대한기계학회논문집A
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• 제24권2호
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• pp.455-463
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• 2000

In order to develop nondestructive techniques for the quantitative estimation of creep damage a series of crept copper samples were prepared and their ultrasonic velocities were measured. Velocities measured in three directions with respect to the loading axis decreased nonlinearly and their anisotropy increased as a function of creep-induced porosity. A progressive damage model was described to explain the void-velocity relationship, including the anisotropy. The comparison of modeling study showed that the creep voids evolved from sphere toward flat oblate spheroid with its minor axis aligned along the stress direction. This model allowed us to determine the average aspect ratio of voids for a given porosity content. A novel technique, the back propagation neural network (BPNN), was applied for estimating the porosity content due to the creep damage. The measured velocities were used to train the BP classifier, and its accuracy was tested on another set of creep samples containing 0 to 0.7 % void content. When the void aspect ratio was used as input parameter together with the velocity data, the NN algorithm provided much better estimation of void content.

• 대한기계학회논문집B
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• 제21권1호
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• pp.174-184
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• 1997

A shock wave, being an irreversible process, gives rise to entropy increase. A great deal of effort has been made to control shock wave and boundary layer interaction related to energy losses as well as problems of vibration and noise. In the present study, tests are performed on a roof mounted half circular arc in an indraft type supersonic wind tunnel to evaluate the effects of porosity, length and depth of cavity in passive control of shock wave on the attenuation of shock strength by reviewing the measured static pressures at the porous wall and cavity. Also the flow field is visualized by a Schlieren system. The results show that in the present study the porosity of 8% produced the largest reduction of pressure fluctuations and that for the same porosity, the strength of shock wave decreases with the increasings of the depth and length of cavity.

• 한국연초학회지
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• 제10권1호
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• pp.83-91
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• 1988

The effects of tipping paper permeability and plugwrap porosity on the ventilation and the pressure drop of cigarettes have been studied and the results obtained were as follows. 1. The single and the multiple regression equation to estimate tip ventilation were establised. In the equations, the observed values of the tip ventilation with the varieties the plugwrap porosity were content with them by the single regression equation. 2. As based on the statistical consideration of the above equation, the deviation of the observed tip ventilation versus the tipping paper permeability were higher than them to the plugwrap porosity. 3. The regression equations to calculate pressure drop ratio and the total ventilation rate in filter tip from the tea ventilation were obtained. According to the equation, the observed values of the pressure drop ratio were significantly similar to them calculated. 4. It was found that the equations could be applied to the calculation of the ventilation of cigarettes using the mechanical and micro laser perforation tipping paper as well as the electrically perforated tipping paper of this Study.