• Title/Summary/Keyword: Porosity improvement

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ACCURACY IMPROVEMENT OF THE BLEED BOUNDARY CONDITION WITH THE EFFECTS OF POROSITY VARIATIONS AND EXPANSION WAVES (다공도 및 팽창파의 영향을 고려한 BLEED 경계조건 수치 모델링의 정확도 향상 연구)

  • Kim, G.;Choe, Y.;Kim, C.
    • Journal of computational fluids engineering
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    • v.21 no.1
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    • pp.94-102
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    • 2016
  • The present paper deals with accuracy improvement of a bleed boundary condition model used to improve the performance of supersonic inlets. In order to accurately predict the amount of bleed mass flow rates, this study performs a scaling of sonic flow coefficient data for 90-degree bleed holes in consideration of Prandtl-Meyer expansion theory. Furthermore, it is assumed that porosity varies with stream-wise location of the porous bleed plate to accurately predict downstream boundary layer profiles. The bleed boundary condition model is demonstrated through Computational Fluid Dynamics(CFD) simulations of bleed flows on a flat plate with/without an oblique shock. As a result, the bleed model shows the improved accuracy of bleed mass rates and downstream boundary layer profiles.

Study on the Improvement of Paper Sludge Dewatering by Adding Wastepaper Powders (고지 분말 첨가에 따른 제지 슬러지의 탈수성 개선에 관한 연구)

  • 이성호;임택준;조준형
    • Journal of Korea Technical Association of The Pulp and Paper Industry
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    • v.34 no.2
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    • pp.47-53
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    • 2002
  • Three types of sludges including printing paper, newsprint and tissue paper were prepared at 5% concentration for filtration-expression operations. Filtration-expression characteristics of sludge were measured in different pressure and wastepaper powder dosage. Specific filtration resistance and porosity were calculated with theoretical formula. Higher pressure increased the progresses of filtration and expression while it decreased porosity. The addition of 5% wastepaper powder more accelerated the progresses of filtration and expression than that of 10% wastepaper powder. The lowest porosity value was also measured at 5% dosage of wastepaper powder. The decrease of porosity implied the decrease of moisture content in cake. The results indicated that dewatering of sludge was efficient in high pressure and 5% dosage of wastepaper powder.

Effect of Change in Open Porosity as a Function of Uniaxial Molding Pressure on Density Improvement After Impregnation (일축가압법으로 벌크흑연 제조 시 성형압력에 따른 열린기공률 변화가 함침 후 밀도 향상에 미치는 영향)

  • Lee, Sang-Min;Lee, Sang-Hye;Roh, Jae-Seung
    • Journal of Powder Materials
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    • v.28 no.1
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    • pp.7-12
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    • 2021
  • The change in the open porosity of bulk graphite as a function of the uniaxial molding pressure during manufacturing is studied using artificial graphite powder. Subsequently, the graphite is impregnated to determine the effect of the open porosity on the impregnation efficiency and to improve the density of the final bulk graphite. Bulk graphite is manufactured with different uniaxial molding pressures after mixing graphite powder, which is the by-product of processing the final graphite products and phenolic resin. The bulk density and open porosity are measured using the Archimedes method. The bulk density and open porosity of bulk graphite increase as the molding pressure increases. The open porosity of molded bulk graphite is 25.35% at 30 MPa and 29.84% at 300 MPa. It is confirmed that the impregnation efficiency increases when the impregnation process is performed on a specimen with large open porosity. In this study, the bulk density of bulk graphite molded at 300 MPa is 11.06% higher than that before impregnation, which is the highest reported increase. Therefore, it is expected that the higher the uniaxial pressure, the higher the density of bulk graphite.

Laboratory experiments on the improvement of rockfill materials with composite grout

  • Wang, Tao;Liu, Sihong;Lu, Yang
    • Geomechanics and Engineering
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    • v.17 no.3
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    • pp.307-316
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    • 2019
  • Dam deformation should be strictly controlled for the construction of 300 m-high rockfill dams, so the rockfill materials need to have low porosity. A method of using composite grout is proposed to reduce the porosity of rockfill materials for the construction of high rockfill dams. The composite grout is a mixture of fly ash, cement and sand with the properties of easy flow and post-hardening. During the process of rolling compaction, the grout admixture sprinkled on the rockfill surface will gradually infiltrate into the inter-granular voids of rockfill by the exciting force of vibratory roller to reduce the porosity of rockfill. A visible flowing test was firstly designed to explore the flow characteristics of composite grout in porous media. Then, the compressibility, shear strength, permeability and suffusion susceptibility properties of composite grout-modified rockfill are studied by a series of laboratory tests. Experimental results show that the flow characteristics of composite grout are closely related to the fly ash content, the water-to-binder ratio, the maximum sand size and the content of composite grout. The filling of composite grout can effectively reduce the porosity of rockfill materials, as well as increase the compression modulus of rockfill materials, especially for loose and gap-graded rockfill materials. Composite grout-modified rockfill tends to have greater shear strength, larger suffusion erosion resistance, and smaller permeability coefficient. The composite grout mainly plays the roles of filling, lubrication and cementation in rockfill materials.

A Numerical Analysis on Pneumatic Fracturing for in-situ Remediation (비포화대 오염정화 설계를 위한 공압파쇄 모사 해석)

  • Kwon, Mi-Seon;Park, Eun-Gyu;Lee, Cheol-Hyo;Kim, Yong-Seong;Kim, Nam-Jin
    • Journal of Soil and Groundwater Environment
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    • v.15 no.6
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    • pp.53-63
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    • 2010
  • Pneumatic fracturing is an emerging tool to enhance the remediation efficiency of contaminated unsaturated zones by injecting high pressure air and inducing artificial fracture networks. Pneumatic fracturing is reported to be well suited for the cases where the contaminated unsaturated zone thickness is less than 5 m as many contaminated domestic sites in Korea. Nevertheless, there have been almost no studies carried out on the site-specific efficiency and the optimized design of pneumatic fracturing considering the unsaturated zone characteristics of Korea. In this study, we employ numerical simulations to compare the efficiency of pneumatic fracturing on the aspect of the site remediation and the porosity improvement at several hypothetic unsaturated zones composed of four typical soil types. According to the simulation results, it is found that the zone with fine grains soil such as clay and silt shows better efficiency than the zone composed of coarse grains in terms of air flow and porosity enhancements. The results imply that pneumatic fracturing may improve the efficiency of site reclamation by jointly or independently applied to the many contaminated sites in Korea.

A Study on the Electrochemical Properties of the Cathode upon Different Kinds of Activated carbon in Zinc/Air Battery (활성탄 종류에 따른 아연공기전지용 Cathode의 전기화학적 특성 연구)

  • 김지훈;엄승욱;문성인;윤문수;김주용;박정식;박정후
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.17 no.4
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    • pp.415-421
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    • 2004
  • The voltage profile of Zinc/Air battery during discharge has very flat pattern in a given voltage range, But, if not enough the porosity in cathode, as a result of that capacity, energy and discharge voltage of batteries become low. Therefore, we focused the pore effects in activated carbon for cathode. We examined discharge voltage, specific capacity, specific energy, resistance and characteristics during the GSM pulse discharge upon different kinds of activated carbon in Zinc/Air battery, Also we measured porosity of the air cathode according to the ASTM. So we achieved improvement of specific capacity, specific energy and discharge voltage according to increase meso pores of activated carbon. We found the optimized activated carbon material for Zinc/Air battery.

Effects of Amounts of Carbon Source and Infiltrated Si on the Porosity and Fracture Strength of Porous Reaction Bonded SiC (침윤된 Si 및 성형체내 Carbon Source의 양이 반응소결 탄화규소 다공체의 기공률 및 파괴강도에 미치는 영향)

  • Yun, Sung-Ho;Tan, Phung Nhut;Kim, Young-Do;Park, Sang-Whan
    • Journal of the Korean Ceramic Society
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    • v.44 no.7
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    • pp.381-386
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    • 2007
  • A porous reaction bonded silicon carbide (RBSC) was fabricated by a molten Si infiltration method. The porosity and flexural strength of porous RBSC fabricated in this study were dependent upon the amount of carbon source used in the SiC/carbon preform as well as the amount of Si infiltrated into the SiC/carbon preform. The porosity and flexural strength of porous RBSC were in the range of $20 vo1.{\sim}49 vo1.%$ and $38{\sim}61 MPa$, respectively. With increase of carbon contents and molten Si for infiltration, volume fraction of the pores was gradually decreased, and flexural strength was increased. The porous RBSCs fabricated with the same amount of molten Si show less residual Si around neck with increase of carbon source, as well as a new SiC was formed around neck which resulted in the decreased porosity and improvement of the flexural strength. In addition, decrease of the porosity and increase of the flexural strength were also obtained by increase of the amount of molten Si with the same amount of carbon source. However, it was found that the flexural strength of porous RBSC depends on the porosity rather than the amount of the newly formed SiC in neck phase between SiC particles used as a starting material.

Economic Evaluation of Crops Grown under Different Soil Improvement Methods in Newly-reclaimed Sloped Land (신개간지(新開墾地) 토양개량방법별(土壤改良方法別) 작물(作物)의 경제성(經濟性) 검정(檢定))

  • Hur, Bong Koo;Kim, Moo Sung
    • Korean Journal of Soil Science and Fertilizer
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    • v.28 no.3
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    • pp.256-260
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    • 1995
  • This study was carried out to select economic-crops according to the improvement methods of newly-reclaimed soils. Silage corn, soybean, Job's tears and sweet potato were cultivated under 6 treatments including integrated improvement plot, control plot, compost plot, subsoiling plot, phosphate plot and lime plot on the Songjeong loam from 1985 to 1988. Crop yields and soil physical properties were investigated throughout the experiment. Soil porosity in the sweet potato plots were highest. In case of cultivated years, those of 4th year were lowest. Averaged yield increasing ratios of silage corn, soybean, job`s tears and sweet potato in the integrated improvement plots were 132%, 29%, 49% and 59%, respectively. And that of 5 soil improved treatments for 4 crops were 53%, 15%, 25% and 38%, respectively. After subtraction of the total expenses of soil conditioners, the economical efficiency of soil improvements were clear in the 4 crops except the compost plot of silage corn. That of sweet potato plot was the highest.

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Effects of Water Quality Improvement by Porosity of Fill Materials in Mattress/Filter System (Mattress/Filter 채움재의 공극률에 따른 하천수질 개선효과)

  • Ko, Jin Seok;Lee, Sung Yun;Heo, Chang Hwan;Jee, Hong Kee
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.1B
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    • pp.51-60
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    • 2006
  • Water quality improvement in mattress/filter system using porous material like slag from industrial activity and zeolite that has been studied for environment improvement and pollution abatement is very useful in polluted stagnant stream channel. Slag is consisted of CaO, $SiO_2$, $Al_2O_3$ and $Fe_2O_3$. Slag with large specific surface area of porosity has been used such as sludge settling and adsorptive materials. Because slag is porous, it can be used for purification filter. As slag is used as filled materials of mattress/filter system and the system has good advantages for the waste water treatment, water recycling, and the improvement of water quality at the same time and so on. Because zeolite has much advantage of cation exchange, adsorption, catalyst and dehydration characteristics, It is used for environment improvement of livestock farms, treatment of artificial sewage and waste water, improvement of drinking water quality, radioactive waste disposal and radioactive material pollution control. In this study, according to verifying effects of water quality improvement of fill materials by porosity that 38.6%, 45.8% and 49.8% respectively in the stagnant stream channel, water quality monitoring of inflow and outflow was conducted on pH, DO, BOD, COD, SS, T-N and T-P. Mattress/filter system was able to accelerate water quality improvement by biofilter as waste water flows through gap of mattress/filter fill materials and by contact catalysis, absorption, catabolism by biofilm. Mattress/filter system used slag and zeolite forms biofilm easily and accelerates adsorption of organic matter. As a result, mattress/filter system increases water self-purification and accelerates water quality improvement available for stream water clean-up.

Evaluation of Durability Performance of Fly Ash Blended Concrete due to Fly Ash Replacement with Tire Derived Fuel Ash (타이어 고무 애쉬 치환에 따른 플라이애쉬 혼입 콘크리트의 내구성능 성능 평가)

  • Kwon, Seung-Jun;Yoon, Yong-Sik;Park, Sang-Min;Kim, Hyeok-Jung
    • Journal of the Korea Concrete Institute
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    • v.28 no.6
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    • pp.647-653
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    • 2016
  • In the paper, durability performance in FA (Fly Ash) blended concrete is evaluated considering replacement of FA with TDFA (Tire Derived Fuel Ash) from 3.0% to 12%. TDFA is a byproduct from combustion process in thermal power plant, where chopped rubber is mixed for boiling efficiency. This is the 1st study on application of TDFA to concrete as mineral admixture. For the work, concrete samples containing 0.5 of w/b (water to binder) ratio and 20% replacement ratio of FA are prepared. With replacing FA with TDFA to 12%, durability performance is evaluated regarding compressive strength, carbonation, chloride diffusion, and porosity. The results of compressive strength, carbonation, and porosity tests show reasonable improvement in durability performance to 12% replacement of TDFA. In particular, clear decreasing diffusion coefficient is observed with increasing TDFA replacement due to its packing effect. Concrete containing TDFA can be effective for durability improvement when workability is satisfied in mixing stage.