화력발전소 장수명화를 위한 부식저감 대책 기술

하정수 한국부식학회 1998 Corrosion Science and Technology Vol.27 No.3

A large percentage of fossil power plants have been in operation for such long durations that they are currently used beyond their of failures that engineer should take into account for the development of life extension technique. Corrosion is one of main concern in old power plants, and causes of breakdown can be stress corrosion cracking, caustic attack, oxygen pitting, hydrogen damage, high temperature corrosion, fire-side corrosion, corrosion fatigue, and the combination of these damages, Understanding the cause of failures can help to prompt corrective measures. Another key ingredient in plant life extension is the remaining-life-assessment technology. To improve the accuracy of life evaluation, corrosion term should be considered and modified with the conventional mechanical terms. This investigation is describing a new method of life evaluation which incorporates corrosion concept for life extension.

Hydroxyapatite와 Al₂O₃ 혼합분말의 상압소결에 의한 TCP/Al₂O₃ 및 Fluorapatite/Al₂O₃ 복합재료의 In-Situ 제조

하정수,한유정,Ha, Jung-Soo,Han, Yoo-Jeong 한국재료학회 2019 한국재료학회지 Vol.29 No.2

A powder mixture of 70 wt% $Al_2O_3$ and 30 wt% hydroxyapatite (HA) is sintered at $1300^{\circ}C$ or $1350^{\circ}C$ for 2 h at normal pressure. An $MgF_2$-added composition to make HA into fluorapatite (FA) is also prepared for comparison. The samples without $MgF_2$ show ${\alpha}$ & ${\beta}$-tricalcium phosphates (TCPs) and $Al_2O_3$ phases with no HA at either of the sintering temperatures. In the case of $1,350^{\circ}C$, a $CaAl_4O_7$ phase is also found. Densification values are 69 and 78 %, and strengths are 156 and 104 MPa for 1,300 and $1,350^{\circ}C$, respectively. Because the decomposition of HA produces a $H_2O$ vapor, fewer large pores of $5-6{\mu}m$ form at $1,300^{\circ}C$. The $MgF_2$-added samples show FA and $Al_2O_3$ phases with no TCP. Densification values are 79 and 87 %, and strengths are 104 and 143 MPa for 1,300 and $1,350^{\circ}C$, respectively. No large pores are observed, and the grain size of FA ($1-2{\mu}m$) is bigger than that of TCP ($0.7{\mu}m{\geq}$) in the samples without $MgF_2$. The resulting $TCP/Al_2O_3$ and $FA/Al_2O_3$ composites fabricated in situ exhibit strengths 6-10 times higher than monolithic TCP and HA.

고분말도 시멘트와 플라이애시를 치환한 콘크리트의 조기강도 발현 특성

하정수,김한식,이영도 한국구조물진단유지관리공학회 2018 한국구조물진단유지관리공학회 논문집 Vol.22 No.2

Cement industries are considered key industries for reducing carbon emissions, and efforts are off the ground to reduce the use of cement in the concrete sector. As a part of this effort, research is off the ground to utilize a large amount of industrial by-products that can be used as a substitute for a part of cement. Concrete using industrial by-products has advantages such as durability, environment friendliness and economical efficiency, but there are problems such as retarding and early-age strength deterioration. Therefore, this study aimed to reduce the use of cement and solve the problem of early-age strength deterioration while using fly ash, which is an industrial by-product. Accordingly, it was confirmed that the strength was improved at all ages irrespective of curing temperature by accelerating the hydration reaction by using high fineness cement. Subsequently, high fineness cement was partially replaced with fly ash and the strength development characteristics were examined. As a result, it was possible to exhibit strength equal to or higher than ordinary portland cement even at the early age. Also, it was confirmed that even when the fly ash is replaced by 30%, it is possible to shorten the time for dismantling the forms of vertical and horizontal members. 시멘트 산업은 탄소배출 감축을 위한 주요 산업분야로 고려되고 있으며, 콘크리트 분야에서 시멘트 사용량 저감을 위한 노력이 진행되고 있다. 이에 대한 노력의 일환으로 시멘트의 일부를 대체하여 사용할 수 있는 산업부산물을 다량으로 활용하기 위한 연구가 진행되고 있다. 산업부산물을 사용한 콘크리트는 내구성, 친환경성 및 경제성 등의 장점을 가지고 있으나, 응결시간 지연, 초기강도 저하 등의 문제점이 있다. 따라서 이 연구에서는 시멘트의 사용량을 줄이고 산업부산물인 플라이애시를 치환하여 사용하면서도 초기강도가 저하되는 문제점을 해결하는 것을 목표로 하였다. 이에 따라, 먼저 고분말도 시멘트 사용에 의한 수화반응 촉진으로 양생온도에 관계없이 모든 재령에서 강도가 증진되는 것을 확인하였다. 이어서 고분말도 시멘트에 플라이애시를 치환하여 강도발현 특성을 검토한 결과, 초기 재령에서도 보통 포틀랜드 시멘트와 비교하여 동등 이상의 강도 발현이 가능하였다. 또한, 플라이애시를 30%까지 치환하여도 수직․수평부재 거푸집 해체 시기를 단축할 수 있는 것을 확인하였다.

Hydrothermal Coating of Hydroxyapatite on ZrO2 Ceramics

하정수 한국세라믹학회 2006 한국세라믹학회지 Vol.43 No.8

Hydrothermal deposition of hydroxyapatite coatings on two types of ZrO 2 substrates (3 mol% Y 2O3-doped and 13 mol% CeO 2-doped tetragonal ZrO 2s) was studied using aqueous solutions of Ca(NO 3)2.4H 2O and (NH 4)2HPO 4 containing EDTA (ethylenediamine tetra acetic acid) disodium salt as a chelating agent for Ca2+ ions. For the precipitation of the coatings, the EDTA-Ca2+chelates were decomposed by oxidation with H 2O2 at 90oC. The deposition behavior, morphology, and orientation of the coatingswere investigated while varying the solution pH using scanning electron microscopy and X-ray diffractometry. For the two sub-strates, sparse deposition of the coating was obtained at pH 5.5, whereas a uniform deposition was obtained at pH 7.1, 9.8, andm lengthor diameter) at pH 7.1, but fine rod-like crystals (1-2m length, 0.1 m diameter) at pH 9.8 and 11.4. The coatings were 1-3 mthick and showed a preferred orientation of the hydroxyapatite crystals with their c axis (i.e., the elongated direction) perpe ndic-ular to the substrate surface especially for pH 9.8 and 11.4.

200MPa급 초고강도 콘크리트의 자기수축 특성에 관한 실험적 연구

하정수,백민수,손유신,이승훈,이영도,정상진 대한건축학회 2011 大韓建築學會論文集 : 構造系 Vol.27 No.8

Low W/B ultra-high strength concrete has low porosity and discontinuous capillary tube in the cement milk. Within a few days after placement, autogenous shrinkage occur because of the quick drying from the self-desiccation. So, the possibility of cracking is higher than the normal strength concrete. In this study, the autogenous shrinkage deformation characteristics of ultra-high strength concrete that are different from the normal strength concrete were examined. A new shrinkage formula is suggested form the experiment data. The conclusion is as follows. 1) The 91days strength of the concrete combination that are W/B 12.5%, normal portland cement 55%, china silica fume 20%, GGBFS-2 20%, anhydrite 5% was the best result, 193.7MPa. So, it is the appropriate combination for the 200MPa grade ultra-high strength concrete. 2) The autogenous shrinkage deformation of W/B 20% ultra-high strength concrete can be predicted using the suggested shrinkage formula.

CFD 검증을 위한 풍동 및 PIV를 이용한 자연환기식온실 내부 공기유동 분석

하정수,이인복,권경석,하태환 (사) 한국생물환경조절학회 2014 생물환경조절학회지 Vol.23 No.4

The number of large scale greenhouses has recently been increasing to cope with mass consumption ofagricultural product. Korean government announced a new development plan for constructing greenhouse complex inreclaimed lands for the purpose of improvement in exports and activation of domestic market of agricultural product. Wind environment in the reclaimed land is totally different from that of inland area, and it can give a strong influence onventilation performance of naturally ventilated greenhouse facilities. In this study, internal airflow analysis of naturallyventilated greenhouse built on a reclaimed land was conducted using wind tunnel and PIV for validation research. Later,the PIV measured results will be used to improve the accuracy of 3 dimensional CFD simulation in the future. Windprofile at a reclaimed land was produced using ESDU program and it was applied to the wind tunnel. The calculatederror was only 5% and 0.96 of correlation coefficient, implying that the computed profiles were designed properly. From the measured results, when external wind speed changed from 1m·s−1 to 1.5m·s−1, air velocities inside the greenhousewhich PIV measured were also increased proportionately in case of both side vent open and side-roof vent open. Considering reduced ratio of air velocity inside the greenhouse, it was measured a minimum of 40% in case of side ventand 30% in case of side-roof vent compared with external wind speed from each vent type. From the quantitative andqualitative PIV analysis, the PIV measured results indicated that there were well ventilated and stagnant areas in thegreenhouse according to external wind condition as well as ventilation design. 본 연구에서는 간척지 풍 환경 특성에 따른 온실의 환기효율 분석 연구에 대한 기초연구로서 단동 양지붕형온실을 대상으로 간척지 풍 환경을 적용한 풍동실험 및PIV 실험을 수행하여 풍속, 환기방식에 다른 온실 내부공기유동 분석을 수행하였다. 실질적인 간척지 풍환경적용을 위하여 ESDU 프로그램을 활용하여 풍속 및 난류 프로파일을 설계하여 풍동실험에 적용하였으며 구현결과 ESDU 대비 5%의 오차 및 상관계수 0.96이 도출되었으며 적절한 오차범위라 판단하여 이를 기준으로 실험을 진행하였다. 벡터장, 컨투어장을 통한 분석 결과, 풍상측에서 유입되는 공기가 온실 하부로 주기류층을 형성하고 온실 상부로는 주풍방향과 반대방향으로 다소 약한 기류를 형성하는 것으로 측정되었다. 이는 환기 시, 온실 하부영역이 가장 환기가 원활한 위치이며 후류가 형성되는 상부영역은 저속의 순환구역으로 온실 내부에 있어 환기에가장 취약한 위치임을 알 수 있었다. 또한 외부풍속 대비 온실 유입구 유속의 경우 상이하게 나타난 바, 이는차후 환기량이나 환기효율의 산정에 있어 보다 실질적인수치가 될 것으로 사료된다. 온실 내부 중앙부 기준 수직 높이에 대한 높이별 유속수치 도출 및 분석결과, 풍속의 증가율에 비례하여 내부유속 분포 수치 또한 비례해서 증가하는 것을 알 수 있었다. 환기방식에 따른 내부 유속 저감 비율은 측창 환기, 측창-천창 환기의 경우 각각 약 40%, 30%로 나타났으며 측창-천창 환기조건에서는 천창을 추가적으로 개방함으로써 공기의 유입되는 면적이 증감함에 따라 온실을기준으로 발생되는 부압이 감소하여 오히려 측창 환기조건보다 더 큰 유속 수치가 도출된 것으로 사료된다. 이는 차후 질량교체 환기량, 추적가스 감쇠법 등의 방법을통한 환기량 산정에 있어 환기방식에 따른 환기량의 변화양상에 대한 분석을 추가적으로 수행할 필요성을 지니는 자료로 판단된다. 본 연구를 통하여 도출된 결과를 바탕으로 전산유체역학(Computational Fluid Dynamics, CFD) 시뮬레이션에 접목하여 앞서 도출된 정량적인 높이별 유속 수치및 정성적 유동분포를 기준으로 검증 및 정확도 향상을통한 환기분석 모델을 설계하고자 하였다. 온실 내부의공기유동에 따른 보다 실질적인 환기 척도를 도출하여다양한 온실형태별, 환경조건별, 환기방식별 환기경향 분석 및 예측이 가능할 것으로 전망되며 시뮬레이션을 활용한 온실 체적 전체 및 구역별 환기량을 예측하여 환기 취약 구역을 파악, 보완할 수 있을 것으로 기대된다.

Processing of Porous Ceramics with a Cellular Structure Using Polymer Beads

하정수,김창삼 한국세라믹학회 2003 한국세라믹학회지 Vol.40 No.12

Two processing routes (i.e., the gel casting and polymer preform routes) using polymer beads were studied to fabricate porous ceramics with a cellular structure. The gel casting route, comprising the gel casting of a ceramic slurry mixed with polymer beads, was found to be inadequate to produce porous ceramic bodies with a interconnected pore structure, due to complete coating of the slurry on the polymer beads, which left just isolated pores in the final sintered bodies. The polymer preform route, involving the infiltration of a polymer beads preform with the ceramic slurry, successfully produced porous ceramics with a highly interconnected network of spherical pores. The pore size of 250 -300 μm was demonstrated and the porosity ranged from 82 to 86%. This process is advantageous to control the pore size because it is determined by the sizes of polymer beads used. Another feature is the avoidance of hollow skeleton, giving a high strength. Two processing routes (i.e., the gel casting and polymer preform routes) using polymer beads were studied to fabricate porous ceramics with a cellular structure. The gel casting route, comprising the gel casting of a ceramic slurry mixed with polymer beads, was found to be inadequate to produce porous ceramic bodies with a interconnected pore structure, due to complete coating of the slurry on the polymer beads, which left just isolated pores in the final sintered bodies. The polymer preform route, involving the infiltration of a polymer beads preform with the ceramic slurry, successfully produced porous ceramics with a highly interconnected network of spherical pores. The pore size of 250 -300 μm was demonstrated and the porosity ranged from 82 to 86%. This process is advantageous to control the pore size because it is determined by the sizes of polymer beads used. Another feature is the avoidance of hollow skeleton, giving a high strength.

화력발전소 정비관리 최적화 방안 연구

하정수,정훈,유근봉,김순교 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.11

Today, there are large number of equipments in power plant and they are very complex and various. So, it is not easy to establish proper policy in maintenance management. Because each plant has its own management policy by different operating environment and culture, we cannot apply same maintenance optimizing method to all plant. In this paper, we will review several method for optimizing maintenance management for plant, especially fossil power plant and consider merits and demerits. Finally, we will study how to optimize it by deciding or changing the maintenance period and method of each equipment(system) with RCM(Reliability Centered Maintenance)

수표교(水標橋) 칼럼 -에너지 경쟁 시대, 나는 에너지다

하정수,Ha, Jeong-Su 대한전기협회 2011 전기저널 Vol.417 No.-

지속적 외래 복막투석중인 말기신부전 환자들에서의 수근관 증후군

하정수,김양욱,김영훈,김영준,박인선 대한내과학회 1999 대한내과학회 추계학술대회 Vol.57 No.-