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An empirical model of the wetted wall fraction in separated flows of horizontal and inclined pipes
Ahn, Taehwan,Moon, Jeongmin,Bae, Byeonggeon,Jeong, Jaejun,Bae, Byounguhn,Yun, Byongjo Elsevier 2018 Chemical engineering science Vol.178 No.-
<P><B>Abstract</B></P> <P>This study reports an experiment to investigate the wetted wall fraction (WWF), which represents the shape of the continuous interface of the air–water stratified and wavy flow regimes, in horizontal and inclined pipes with an inner diameter of 40 mm. Using the experimental data, a semi-empirical model to predict the WWF was developed based on the energy balance for the liquid phase in separated flows. The model used a relationship between the WWF and the center of gravity of the liquid phase with a concave interface that can describe continuous changes to the flow regime from a stratified to an annular. The coefficients of the model were empirically determined based on a wide range of experimental data from the literature obtained in the air and various liquids covering a void fraction of greater than 0.79, a pipe with inner diameter in the range 24–150 mm, density differences varying from 812 to 1052 kg/m<SUP>3</SUP>, a range of liquid phase viscosity of 0.87–5.66 mPa s, surface tension ranging from 27.9 to 72.7 mN/m, a wide range of inclination angles from −27° for a downward flow to +3° for an upward flow, and gas and liquid Reynolds numbers based on a superficial velocity of up to 219,000 and 7500, respectively. This WWF model was tested using an extensive experimental database of the WWF and void fraction in the stratified and wavy flow regimes, and yielded the best agreement compared with existing models in the literature.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Circumference distribution of liquid film thickness was measured in inclined pipes. </LI> <LI> Empirical coefficients in a concave interface model were derived to predict the wetted wall fraction. </LI> <LI> Eight prediction models for the wetted wall fraction were investigated and evaluated. </LI> </UL> </P>
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Steam condensation in horizontal and inclined tubes under stratified flow conditions
Ahn, Taehwan,Kang, Jinhoon,Bae, Byeonggeon,Jeong, Jae Jun,Yun, Byongjo Elsevier 2019 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.141 No.-
<P><B>Abstract</B></P> <P>In this study, an experiment on condensation heat transfer was conducted to develop a condensation model considering the structure of separated flow patterns. Multidimensional local condensation heat transfer parameters were measured in pure saturated steam at pressures of 1–5 bar and mass fluxes of 10–50 kg/m<SUP>2</SUP> s in an inclinable tube with an inner diameter of 40 mm and a length of 3 m. A heat partition angle, which separated the upper and lower heat transfer areas for film condensation and convective heat transfer in stratified flow, was obtained based on the inflection point of the circumferential distribution function of local heat flux. A new condensation heat transfer model consisting of the heat partition angle and heat transfer coefficient correlations was developed based on the local heat transfer data. The experimental data for model development were obtained using circular tubes with inner diameters of 30–45 mm and inclination angles of 0–10° under pure saturated steam conditions at pressures of 1–67 bar and mass fluxes of 10–329 kg/m<SUP>2</SUP> s. The model predicted the average heat transfer coefficient with an average deviation of 6.2% against the present experimental data.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Condensation heat transfer models often neglect the structure of flow patterns. </LI> <LI> Local heat transfer parameters were measured inside a condensation tube. </LI> <LI> Heat partition angle was used to separate heat transfer areas in condensation tube. </LI> <LI> A condensation model was developed that accounts for flow channel inclination. </LI> <LI> Model predictions and experimental findings agreed well. </LI> </UL> </P>
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안태환(Ahn, Taehwan) 부산대학교 인문학연구소 2012 코기토 Vol.- No.71
신자유주의 글로벌 자본주의의 헤게모니 체제는 대의 민주주의를 공격하여 어떤 의미에서 “저 강도 민주주의”를 결과하고 있다. 근대성과 민주주의의 개념을 둘러싸고 ‘북’과 ‘남’사이에는 많은 치이가 있다. 보아벤투라 데 소우사 산토스는 유럽 중심적 인식론적 근대성에 기초한 현재의 헤게모니적 사회과학은 사회적 해방이 추구하는 방향을 해석하고 분석하는데 있어 아주 작은 유효성만을 보이고 있다고 인식하고 있다. 따라서, “상호 문화적 번역”의 과제를 통해 근대성의 동일성을 극복할 수 있는 새로운 인식론적 민주적 상상력을 얻어내기 위해 급진적 전환이 필요하다. 그것은 새로운 보편적 담론을 수립하려는 것이 아니다. 세계에 존재하는 복수의 보편적 담론들 사이에서 서로를 이해하는 것을 의미한다. 만약, 우리가 ‘지금, 여기’를 바라본다면 우리는 무감각한 이성, 환유적, 확장적 이성과 같은 근대성의 시각들이 지나치게 미래를 강조하고 현재를 축소시키면서 세계를 식민화 시키고 차별한다는 것을 인식할 수 있다. 그러므로 현재를 확장하고 동질적 “보편주의” 대신에 “코스모폴리탄적 이성”과 “복수-보편성”의 꿈을 가질 필요가 있다. 그런데 그 꿈의 사회적 주체는 예를 들어, 라틴아메리카 사회운동에서 출현하는 집단적 주체이다. 배제된 대중, 결국 민주주의는 대의민주주의와 참여민주주의의 병행에 있다. The hegemonic regime of the neoliberal and global capitalism may attack the representative democracy which results in ‘the democracy of low intensity’ in some sense. There are a lot of difference around the concept of the modernity and the democracy between the perspectives of the ‘north’ and the ‘south’. Boaventura De Sousa Santos realizes that the ac-tual hegemonic social sciences based on the eurocentric epistemological modernity may have little validity on analyzing and interpreting the directions for which the social emanci-pation would seek. Therefore it is necessary to take some radical turn into new epistemological and demo-cratic imaginations overcoming the monoculture of the modernity through the “intercultural translation”. It does not mean to establish new universal discourses but to understand mutually themselves among the plural ones in the world. If we would see ‘the now and here’, we could realize that the optics of the modernity such as reason of indolence, metonymy and proleptic colonize and discriminate the world emphasizing too much the future and contracting the present. It is necessary to amplify the present and to have a dream with a “cosmopolitan reason” and “Plural-universalism” instead of homogeneous “Universalism”. Its social agent is, for example, the collective subject which emerges in the Latin-American social movements: the excluded people. The democracy must be paralleled between the representative and the participatory one.
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라틴아메리카 문화와 대중의 독특한 성격 : 공동성(the communal)
안태환(Taehwan Ahn) 한국문화연구학회 2021 문화연구 Vol.9 No.2
이 논문은 유럽적, 보편적 성격과 매우 다른 독특함(공동성)을 가진 라틴아메리카 문화와 대중의 정체성이 어떤 역사적 맥락에서 형성되었는지를 분석한다. 16세기의 스페인의 정복 이전에 원주민의 독특한 문화 예를 들어, 아이유와 밍가의 공동체적 성격이 식민 시기에도 크게 훼손되지 않고 현재까지 이어져온 것에 주목한다. 식민시기 초반에 백인/원주민 문화가 이중적으로 분리되었다가 17세기에 인종 간 혼혈이 일어나면서 백인 후손인 크리오요와 원주민계와 아프리카계 혼혈 대중이 한 동네에 산다. 그러나 19세기 후반 자유주의에 근거한 근대국가 건설이 시작되면서 상기 대중은 배제된다. 1980년대에 다시 신자유주의에 의해 대중이 배제되자 이에 대해 대중은 강력히 저항한다. 대표적인 예가 볼리비아의 물 전쟁이다. 특히 볼리비아의 변혁세력이 과거의 아이유 공동체를 마르크스의 코뮨주의와 결합하여 재구성하려는 “공동체적 사회주의”운동을 보인다. 이는 유럽의 이론적 성격이 강한 코뮨주의와 다르고 1990년대 이후 공통체적 새로운 사회운동의 상호이익의 추구와 다르게 가난한 대중이 사회정의의 실현을 위해 공동성을 실천하는 것이다. This article analyzes how the identity of Latinamerican culture and people has taken the evolutionary process in what historical context. Before the Spanish conquest of the 16th century, we notice that the peculiar culture of the indigenous people that is, the communal character for example, Ayllu and Minga, etc., has been preserved until now, not damaged so even though during the colonial period. In the first part of the colonial period, the cultures of the white people and the indigenous had been separated but in the 17th century, the Creole of the white descendents and the people of the lineal mestizo of the indigenous and that of the african had lived together in the same district of the cities. But in the latter part of the 19th century the construction of the modern state by the liberalism, had begun the exclusion of the people mentioned above and when the people again excluded by the neoliberalism at 1980s, pretty soon the people had resisted strongly. For example, we can see the War of Water in Bolivia. Especially the group of the radical transformation of Bolivia shows the movements of the “communitarian socialism” to reconstitute of the Ayllu community with the communism of Marx. It is different from the European communism which has strong theoretical tendencies and also it means the practice of the communal to realize the social justice of the poor people instead of searching for the mutual interests of the new social movements of the common wealth begun after the 1990s in Europe.
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안태환(Ahn TaeHwan) 한국지역개발학회 1993 韓國地域開發學會誌 Vol.6 No.2
The purpose of this paper is to examine the meaning, necessity and types of the public-private partnership(PPP) and to analyze a case study on the urban development on the foreign countries and Korea. This study also attempts to identify the major problems and tasks on applying the PPP into urban and regional development field in Korea. Since 1980`s, it has been recognized to induce the private fund and skill into the public development sector. Thus America and England used PPP as a method of promoting regional economic growth and urban renewal projects. In particular, Japan used the third sector as an another form of PPP. In this study, the development cases in foreign countries are examined in terms of PPP perspectives and found some characteristics as follows : (1) waterfront renewal and land reclamation are most typical projects in major cities. (2) most projects are planned and constructed for foreign, future, and information oriented districts. (3) most sites are propelled with various development techniques. (4) public corporation has strong powers of the initiative and management to implement the projects. Thus local public corporation, transportation related facilities, privatalization of public service and the third sector projects in Korea are examined on the necessity, major problems, and tasks of PPP, etc. The major findings are followings : it is needed to (1) understand the necessity of partnership and establish the new morals and philosophies for higher level of partnership ; (2) consider the character and priority of projects, geographical coditions, etc. ; (3) specify the merit of public or private sector for implementing partner ship ; (4) give the participants various incentives ; (5) revise the legal, financial, and tax supporting system for promoting partnership.
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