• Journal of the Korean Wood Science and Technology
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• v.31 no.4
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• pp.8-15
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• 2003

This study was carried out to investigate the dimensional stability of wood treated with PEG for better utilization of domestic small-diameter logs. Four species of ring- porous wood(Quercus mongolica F_ISCH, Quercus variabilis B_LUME, Fraxinus rhynchophylla H_ANCE, Paulownia coreana U_YEKI,) and four species of diffuse-porous wood(Prunus sargentii R_EHDER, Betula davurica P_ALL, Populus tomentiglandulosa T. L_EE, Cornus controversa H_EMSLEY) were used for this experiment. The shrinkage of wood decreased with increasing the concentration of PEG. The shrinkage of diffuse- porous woods was lower than that of ring-porous woods. The weight gain increased in proportional to the PEG concentration. Diffuse-porous woods showed a little higher weight gain than ring-porous woods. Bulking effect also increased with increasing the PEG concentration, but was in inverse proportional to the molecular weight of PEG. Diffuse-porous woods showed higher bulking effect than ring-porous woods. Consequently, diffuse-porous woods showed better dimensional stability than ring- porous woods. It was considered that dimensional stability was affected by characteristics of wood such as vessel and tylosis, and density.

• International Journal of Concrete Structures and Materials
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• v.18 no.2E
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• pp.117-124
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• 2006

Porous concrete has been used recently for the purpose of decreasing the load on the earth environment. It consists solely of cement, water and coarse aggregate of uni form size. Its fundamental properties are considerably affected by the physical properties of aggregate because the aggregate is the main material for the most part in its mix proportion. Because of this reason, this study carried out an investigation of the influence of the size and type of aggregate on the fundamental properties of porous concrete. It is shown that the fundamental properties of porous concrete was seldom affected by the size of aggregate except for the case of using $2.5{\sim}5mm$ aggregate but varied significantly by the type of aggregate. In particular, the compressive strength of porous concrete using $2.5{\sim}5mm$ aggregate was much higher than that using other aggregate, and its void ratio and coefficient of permeability was lower. Moreover, the capacity to maintain the permeability of porous concrete was found to vary by the size and type of aggregate. Of particular notice was that it decreased greatly when $2.5{\sim}5mm$ aggregate was used. Unlike ordinary concrete, porous concrete exhibited very high dynamic modulus of elasticity at early age and continued to increase but slowly afterwards.

• Journal of the Korean Ceramic Society
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• v.39 no.10
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• pp.919-927
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• 2002

In order to fabricate double-layered porous materials powders of different particle sizes were pressed stepwise. Ford＇s equation which predicts the fired density with the change in pressed density was employed in order to adjust the difference in sintering shrinkage of the green body with double-layered porous structure. Double-layered porous materials were characterized by investigating microstructures and permeability. SEM micrographs showed the distinct difference in pore sizes of double-layered porous material. Permeability of single-layered porous material increased by increasing the starting particle sizes and porosity as well. Permeability of the double-layered porous material depends largely on the layer of small pore diameter.

• Journal of Power System Engineering
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• v.11 no.2
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• pp.20-25
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• 2007

The performance of air-to-air heat exchanger has been investigated with rotating porous plates newly developed in this study. With an equal interval of 18 mm, the rotating porous plates are installed inside the heat exchanger where the hot and cold airs enter at opposite ends. When flowing in opposite directions by the separating plate installed in the center of the rotating porous plates, the airs give and receive the heat each other. Dry bulb temperature is set by adjusting heat supply at heater. In order to measure the temperature distribution of the hot air side inside heat exchanger, the thermocouples are inserted between the plates. The first location of thermocouple is 10mm downstream from the inlet of heat exchanger, and succeeding ten locations are aligned at an equal interval of 18mm. From the experiment of air-to-air heat exchanger with the rotating porous plates, the heat transfer rate increased as both air flow rate and RPM of the rotating porous plate increased. It was found that the overall heat transfer coefficient increased with the increase in RPM of porous plate at the conditions of the same air flow rate.

• Design & Manufacturing
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• v.11 no.1
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• pp.30-33
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• 2017

In this study, the mold technology for manufacturing of porous implant was investigated. Firstly, we considered the concept of insert molding technology with 3D printing of porous inert part. The part on implant was designed in the end region of the implant. And then main implant bodies were manufactured using conventional machining method. The other porous parts were designed and optimized with molding simulation. As the feature size of porous implant was so small that perfect feature of it using 3D printing technology could not be obtained. So, we proposed another scheme for manufacturing of the porous implant in the replace of the former approach. Polymer mold cores with 3D printing technology were considered. The effects of addictive manufacturing process parameters on the properties of mechanical and dimensional accuracy were investigated. Direct 3D printed polymer mold cores were designed and manufactured under the simulation of thermal and molding analysis. It was shown that 3D printed mold core with polymer could be adapted to the injection molding for porous implant.

• Journal of the Korean Ceramic Society
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• v.41 no.5
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• pp.359-363
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• 2004

Photoluminescence excitation (PLE) spectroscopy studies were performed for anodically etched porous Zn, which exhibited a PL in the blue/violet spectral range peaking at 420 nm (2.95 eV), and oxidzed porous Zn at 380$^{\circ}C$ for 10 min and 12 h. A broad absorption band was observed at 4.07 eV (305 nm), 3.49 (355 nm) for anodically etched porous Zn. In contrast, both the oxidized porous Zn and sintered ZnO exhibited an almost identical one broad absorption band at 3.85 eV (322 nm), when PLE spectra were measured at 378 nm (3.28 eV). The oxidized porous Zn and sintered ZnO, which displayed both UV and green luminescence band, showed an additional absorption band at 389 nm (3.19 eV) and 467 nm (2.66 eV). In contrast, no significant absorption band was detected for a 10-min oxidized porous Zn, which only displayed one UV luminescence void of deep-level luminescence. These absorption bands determined by PLE studies enabled a clear understanding of an emission mechanism for the UV and green luminescence from ZnO.

• Journal of Ocean Engineering and Technology
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• v.18 no.5
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• pp.7-14
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• 2004

The interaction of incident manochromatic waves with an array of N surface-piercing porous dual cylindrical structures is investigated in the frame of three-dimensional linear potential theory. The dual cylindrical structure is camposed of concentric two cylinders. The exterior cylinder is porous and the interior cylinder is impermeable. The fluid domain is divided into N+1 regions i.e. a single exterior region and N interior regions. The diffraction potentials in each region representing the scattering of incident waves by an array of porous cylindrical structures are expressed by the Fourier Bessel series. The unknown coefficients in each region are determined by applying the porous boundary condition and continuity of mass flux at the matching boundary. It is found that an array of porous cylindrical structures reduces both the wave forces and the wave run-up, and shows the excellent performance of wave blocking. The results show that various types of breakwater exchanging seawater are prospective by controlling the porosity and the configuration of cylindrical structures.

• Journal of the Korean Ceramic Society
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• v.45 no.12
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• pp.832-838
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• 2008

Diatomite, bentonite and zeolite were used as porous materials for fabricating hygroscopic panels. Moisture adsorption and desorption of porous materials were investigated and hydrothermal method was applied to fabricate panels. Cheolwon diatomite and Pohang zeolite showed excellent characteristics of moisture adsorption and desorption. These characteristics were caused by higher surface area and pore volume of porous materials. Correlation coefficient between surface area and moisture adsorption content of porous materials was 0.93. Moisture adsorption contents were influenced by surface area and pore volume of panels, and surface area more effected on moisture adsorption. Correlation coefficient between surface area and moisture adsorption content of panels was 0.86. Moisture adsorption content of panel with 10% Pohang zeolite was $180\;g/m^2$ and that of 10% Cheolwon diatomite was $170\;g/m^2$. Moisture desorption content of panel with 10% Pohang zeolite was $105\;g/m^2$. Moisture adsorption contents of panel with porous materials were higher than that of panel without porous materials.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.622-624
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• 2008

This investigation studies the effects of material properties and corresponding propagation wave types on optimal configurations of sound absorbing porous materials in maximizing the absorption performance by topology optimization. The acoustic behavior of porous materials is characterized by their material properties which determine motions of the frame and the air. When the frame has a motion, two types of compressional wave propagate in the porous material. Because each wave in the material make different influence on the absorption performance, it is important to understand the relative contribution of each wave to the sound absorption. The relative contribution of the propagating waves in a porous material is determined by the material properties, therefore, an optimal configuration of a porous material to maximize the absorption performance is apparently affected by the material properties. In fact, virtually different optimal configurations were obtained for absorption coefficient maximization when the topology optimization method developed by the authors was applied to porous materials having different material properties. In this investigation, some preliminary results to explain the findings are presented. Although several factors should be considered, the present investigation is focused on the effects of the material properties and corresponding propagation waves on the optimized configurations.

• Korean Journal of Materials Research
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• v.28 no.1
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• pp.62-67
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• 2018

Active clay, bentonite and zeolite were used as porous materials for humidity controlling ceramic boards. The specific area and the pore volume of active clay were higher than bentonite and zeolite. The flexible strength of the gypsum board decreased with an increasing amount of porous material, and the flexible strength was lowest when active clay with a higher specific surface area than others porous materials was added. The specific surface area and total pore volume of ceramic boards containing porous material were highest at $102.25m^2/g$, $0.142cm^3/g$, respectively, when the active clay was added. In addition, as the amount of added porous materials increased, the specific surface area and total pore volume of the ceramic board increased, but the average pore diameter decreased. The addition of s porous materials with a high specific area and a large pore volume improved the moisture absorptive and desorptive performance of the ceramic board. Therefore, in this experiment, the moisture absorptive and desorptive properties were the best when active clay was added. Furthermore, as the amount of added porous materials increased, the moisture absorptive and desorptive properties improved. When 70 mass% of active clay was added to ${\alpha}$-type gypsum, the hygroscopicity was the highest, about $300g/m^2$, in this experiment.