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Jo, Daeseong,Al-Yahia, Omar S.,Altamimi, Raga'i M.,Park, Jonghark,Chae, Heetaek Korean Nuclear Society 2014 Nuclear Engineering and Technology Vol.46 No.2
Heat transfer characteristics in a narrow rectangular channel are experimentally investigated for upward and downward flows. The experimental data obtained are compared with existing data and predictions by many correlations. Based on the observations, there are differences from others: (1) there are no different heat transfer characteristics between upward and downward flows, (2) most of the existing correlations under-estimate heat transfer characteristics, and (3) existing correlations do not predict the high heat transfer in the entrance region for a wide range of Re. In addition, there are a few heat transfer correlations applicable to narrow rectangular channels. Therefore, a new set of correlations is proposed with and without consideration of the entrance region. Without consideration of the entrance region, heat transfer characteristics are expressed as a function of Re and Pr for turbulent flows, and as a function of Gz for laminar flows. The correlation proposed for turbulent and laminar flows has errors of ${\pm}18.25$ and ${\pm}13.62%$, respectively. With consideration of the entrance region, the heat transfer characteristics are expressed as a function of Re, Pr, and $z^*$ for both laminar and turbulent flows. The correlation for turbulent and laminar flows has errors of ${\pm}19.5$ and ${\pm}22.0%$, respectively.
Jo, Hongrae,Jo, Daeseong Elsevier 2017 Annals of nuclear energy Vol.110 No.-
<P><B>Abstract</B></P> <P>In this study, smooth bubble condensation that occurs in subcooled pool water was examined to understand condensation phenomena at the beginning of boiling. The behaviors of condensable and non-condensable bubbles were investigated with respect to various temperatures and bubble sizes. The experimental data were analyzed using visual and acoustic methods including Phase Interface Binarization (PIB), Tridimensional Reconstructing Assumption (TRA), and acoustic data conversion. For visual analyses, (1) the PIB method determined bubble departure frequency, condensation time, and rising distance, and (2) the TRA method determined departure bubble size and volume reduction rate. The bubble detached with smaller volume and occurred more frequently with a smaller nozzle and a higher subcooling degree. Because the condensation always occurred during the growth, necking, and detachment of a bubble, the bubble was detached before it grew sufficiently. Lower condensation time and rising distance were associated with higher subcooling degrees and smaller injected bubbles. With respect to the acoustic analysis, sound signals were measured using a hydrophone, and the obtained analog data were converted to sound pressure units. The results revealed that higher volume reduction rate resulted in stronger sound pressure. As a result, the condensation phenomena in the smooth bubble regime were visually observed, and the possibilities of acoustic monitoring for earlier boiling were investigated.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Smooth bubble condensation was examined in subcooled water. </LI> <LI> Visual and acoustic analysis methods were used to examine the condensation phenomena. </LI> <LI> Phase Interface Binarization determined bubble occurrence frequency, condensation time, and rising distance. </LI> <LI> Tridimensional Reconstructing Assumption determined departure bubble size and condensation rate. </LI> <LI> Acoustic analysis indicated differences in acoustic signals among various condensation conditions. </LI> </UL> </P>
조홍래(Hongrae Jo),조대성(Daeseong Jo) 한국가시화정보학회 2016 한국가시화정보학회 학술발표대회 논문집 Vol.2016 No.12
Characteristics of collapsing vapor bubble in subcooled pool water were experimentally investigated in various subcoolings; 1K, 10K, and 20K, with different bubble sizes. In the present study, the collapsing processes were recorded by a high-speed camera. Acquired data were analyzed using Phase Interface Binarization (PIB), and 3D Reconstructing Assumption (TRA). The occurrence frequencies of bubble, rising distances and condensation times were investigated by PIB analysis. Moreover, the volume of bubbles and volumetric flow rate were calculated by TRA analysis. Based on these results, the fundamental phenomena of earlier boiling were known.
Gate-tunable nonreciprocal response in noncentrosymmetric LaAlO₃/SrTiO₃ interfaces
Daeseong Choe,Mi-Jin Jin,Shin-Ik Kim,Hyung-Jin Choi,Junhyeon Jo,Inseon Oh,Jungmin Park,Hosub Jin,Hyun Cheol Koo,Byoung-Chul Min,Suk-Min Hong,Hyun-Woo Lee,Seung-Hyub Baek,Jung-Woo Yoo 한국자기학회 2019 한국자기학회 학술연구발표회 논문개요집 Vol.29 No.2
Gate-tunable large nonreciprocal charge transport in noncentrosymmetric LaAlO₃/SrTiO₃ interfaces
Daeseong Choe,Mi-Jin Jin,Shin-Ik Kim,Hyung-Jin Choi,Junhyeon Jo,Inseon Oh,Jungmin Park,Hosub Jin,Hyun Cheol Koo,Byoung-Chul Min,Suk-Min Hong,Hyun-Woo Lee,Seung-Hyub Baek,Jung-Woo Yoo 한국자기학회 2020 한국자기학회 학술연구발표회 논문개요집 Vol.30 No.2
멀티 마이크로폰 기반 원격지 간 화상회의 시선 일치 기법
이대성(Daeseong Lee),조동식(Dongsik Jo) 한국정보통신학회 2021 한국정보통신학회 종합학술대회 논문집 Vol.25 No.2
최근, 대면 회의를 대체할 수 있는 수단으로 원격지 간 화상 회의 시스템의 활용도가 높아졌다. 기존 화상회의 시스템은 원격지 사용자의 시선 불일치로 인해 몰입감 있는 화상회의 환경을 제공하기에는 한계를 가지고 있다. 따라서, 서로 다른 원격지 간 참여자의 시선 정보를 일치하여 화상 회의의 몰입도를 높일 수 있는 기술 적용이 필요하다. 본 논문에서는 원격지 간 화상회의 참여자의 시선을 일치하기 위해 로컬에 설치된 멀티 마이크로폰 기반으로 화자의 위치를 추정하여 시선이 일치된 화상회의 영상을 구현하는 기술을 제안한다. 본 연구논문의 방법을 이용하면 원격지 간 화상회의 뿐 아니라 로봇 상호작용, 가상 휴먼 인터페이스 등 다양한 분야에 확대 적용될 수 있을 것으로 본다. Recently, as an alternative to replace face-to-face meetings, video conferencing systems between remote locations has increased. However, video conferencing systems have limitations in terms of mismatch of the eyes of remote users. Therefore, it is necessary to apply a technology that can increase the level of immersion in video conferences by matching the gaze information of participants between different remote locations. In this paper, we propose a novel technique to realize video conferencing with the same gaze by estimating the speaker’s location based on a multi-microphone. Using our method, it can be applied to various fields such as robot interaction and virtual human interface as well as video conferencing between remote locations.
ONB, OSV, and OFI for subcooled flow boiling through a narrow rectangular channel heated on one-side
Al-Yahia, Omar S.,Jo, Daeseong Pergamon Press 2018 International journal of heat and mass transfer Vol. No.
<P><B>Abstract</B></P> <P>This paper presents an experimental investigation of the thermal hydraulic thresholds of the subcooled boiling instability in forced convective flow, such as the onset of nucleate boiling (ONB), the onset of significant void (OSV), and the onset of flow instability (OFI). The experiment was constrained to water flows in the upward direction under atmospheric pressure through a narrow rectangular channel heated on one-side having a gap of 2.35mm, a width of 54mm, and length of 566mm. The heated length and width were 300mm and 50 mm, respectively. The experiment was performed over a wide range of inlet temperature (35–65°C), mass fluxes (118–1400kg/(m<SUP>2</SUP>s)), and heat fluxes (50–650kW/m<SUP>2</SUP>). Two experimental methods were adopted to achieve and identify the ONB, OSV, and OFI: (1) the constant mass flow rate approach and (2) the constant heat flux approach. The results showed consistency between the two methods. The ONB was identified through visualized monitoring using a high-speed camera and by using the slope of the wall temperature deviation method. The ONB was predicted by Jens and Lottes’ correlation. The OSV was detected using the high-speed camera and the wall temperature–heat flux curve. Based on the experimental method, the OFI was identified using pressure drop and inlet pressure fluctuation. The data showed that the OSV and OFI could occur at similar points based on the experimental conditions. Furthermore, the OSV models, such as the modified Bowring model and Saha and Zuber’s model, can be used to predict the OFI. Additionally, some OFI correlations showed good agreement with the present data. However, many other correlations underestimated the OFI results, which might have been a result of differences in the experimental parameters. Therefore, a new empirical correlation that predicted the present data and other experimental data within very good accuracy was suggested. The present study describes and discusses the influence of the experimental parameters; inlet subcooling, mass flow rate, and the imposed heat flux on the ONB, OSV, and OFI incipience.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Experimental study on ONB, OSV, and OFI incipient for a narrow rectangular channel heated from one side has been conducted. </LI> <LI> Constant mass flux approach is consistent with constant heat flux approach. </LI> <LI> ONB occurs earlier than OSV and OFI, however, OSV and OFI may occur at the same moment. </LI> <LI> The influence of mass flux, heat flux, and inlet subcooled temperature on the ONB, OFI phenomena is observed. </LI> <LI> A new correlation is developed to predict the OFI mass flux and OFI heat flux. </LI> </UL> </P>