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Yoon, Juhyeon Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.11
Sizing the tube inlet orifice of a Once-Through Steam Generator (OTSG) is important to protect the integrity of the tubes from thermal cycling and vibration wear. In this study, a new sizing criterion is proposed for the tube inlet orifice to suppress the parallel channel instability in an OTSG. A perturbation method is used to capture the essential parts of the thermal-hydraulic phenomena of the parallel channel instability. The perturbation model of the heat transfer regime boundaries is identified as a missing part in existing models for sizing the OTSG tube inlet orifice. Limitations and deficiency of the existing models are identified and the reasons for the limitations are explained. The newly proposed model can be utilized to size the tube inlet orifice to suppress the parallel channel instability without excessive engineering margin.
A concept of stretchable coaxial cable based on one-body Au nanonetworks
Juhyeon Kim,Byeunggon Kim,Jakyung Eun,Beom-Jin Yoon,Sangmin Jeon,Yun Seon Do,Soo-Hwan Jeong 한국공업화학회 2023 Journal of Industrial and Engineering Chemistry Vol.124 No.-
Recently, the demand for wearable electronics has sharply been increasing for diverse purposes. For theentire system to process enormous data simultaneously between the devices, the importance of stretchableinterconnects with large bandwidth has been emphasized. However, achieving an appropriate attenuationlevel as well as stable transmission performance against elongation is still challenging. This reportsuggests the stretchable coaxial cable based on the one-body metal network, which is intrinsicallystretchable and highly conductive. By multiple wrapping of the one-body metal network, excellent connectivityand electrical conductivity were realized. Its sheet resistance reached as low as that of the solidcylindrical metal. The low-loss cable was obtained through a simple fabrication procedure; its attenuationat 1 GHz remained under 0.011 and 0.033 dB/mm against 0% and 20% elongation, respectively. Also, it only experienced an insignificant change of the attenuation level (3.0%) during 100 stretching/releasing cycles, implying its feasibility of the dynamic connections in prospective applications.
Ahn, Juhyeon,Susanto, Dieky,Noh, Jae-Kyo,Ali, Ghulam,Cho, Byung Won,Chung, Kyung Yoon,Kim, Jong Hak,Oh, Si Hyoung Elsevier Sequoia 2017 Journal of Power Sources Vol. No.
<P><B>Abstract</B></P> <P>In this study, we target to find a new composition for a layered mixed metal oxide, which has a high structural stability and a good electrochemical performance. Our strategy is to alter the transition metal composition focusing on the relative amounts of redox active Ni and Co to the inactive Mn, based on highly-stabilized LiNi<SUB>1/3</SUB>Co<SUB>1/3</SUB>Mn<SUB>1/3</SUB>O<SUB>2</SUB>. X-ray absorption near-edge structure and X-ray diffraction analyses show that the degree of cation disorder decreases on increasing the ratio of Ni and Co to Mn, by the presence of Ni<SUP>3+</SUP>, suggesting that slightly higher Ni and Co contents lead to improved structural stability. Electrochemical studies demonstrate that LiNi<SUB>0.4</SUB>Co<SUB>0.4</SUB>Mn<SUB>0.2</SUB>O<SUB>2</SUB> cathodes exhibit considerable improvements in both the reversible capacity and the rate capabilities at a voltage range of 2.5–4.6 V. <I>In situ</I> XRD measurements reveal that LiNi<SUB>0.4</SUB>Co<SUB>0.4</SUB>Mn<SUB>0.2</SUB>O<SUB>2</SUB> maintains a single-phase and undergoes lesser structural variations compared to controlled compositions during a delithiation process up to 4.6 V, while achieving a high reversible capacity over 200 mAh g<SUP>−1</SUP>. As a result, LiNi<SUB>0.4</SUB>Co<SUB>0.4</SUB>Mn<SUB>0.2</SUB>O<SUB>2</SUB> experiences fewer structural degradations during electrochemical cycling, which explains the excellent long-term cycling performance.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Composition of layered oxides are tuned for high capacity and rate capability. </LI> <LI> LiNi<SUB>0.4</SUB>Co<SUB>0.4</SUB>Mn<SUB>0.2</SUB>O<SUB>2</SUB> is proposed as one of the promising cathode materials. </LI> <LI> Lesser structural changes during charging lead to excellent cycling stability. </LI> <LI> LiNi<SUB>0.4</SUB>Co<SUB>0.4</SUB>Mn<SUB>0.2</SUB>O<SUB>2</SUB> delivers a capacity over 200 mAh g<SUP>−1</SUP> via single-phase reaction. </LI> </UL> </P>
Ahn, Juhyeon,Kim, Jong Hak,Cho, Byung Won,Chung, Kyung Yoon,Kim, Sangryun,Choi, Jang Wook,Oh, Si Hyoung American Chemical Society 2017 NANO LETTERS Vol.17 No.12
<P>Battery performance, such as the rate capability and cycle stability Of lithium transition metal oxides, is strongly correlated with the surface properties of active particles. For lithium-rich layered oxides, transition metal segregation in the initial state and migration upon cycling leads to a significant structural rearrangement, which eventually degrades the electrode performance. Here, we show that a fine-tuning of surface chemistry on the particular crystal facet can facilitate ionic diffusion and thus improve the rate capability dramatically, delivering a specific capacity of similar to 110 mAh g(-1) at 30C. This high rate performance is realized by creating a nanoscale zirconium-abundant rock-salt-like surface phase epitaxially grown on the layered bulk. This surface layer is spontaneously formed on the Li+ diffusive crystallographic facets during the synthesis and is also durable upon electrochemical cycling. As a result, Li-ions can move rapidly through this nanoscale surface layer over hundreds of cycles. This study provides a promising new strategy for designing and preparing a high-performance lithium-rich layered oxide cathode material.</P>
Performance Analysis of a Once-Through Steam Generator for Constant Thermal Power Operation
Hun Sik Han(한훈식),Juhyeon Yoon(윤주현),Young In Kim(김영인) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
A numerical study is made of the operation strategy of a once-through steam generator considering degradation in the thermal-hydraulic performance. The performance of the steam generator is gradually degraded as it experiences fouling, clogging, and plugging during its lifetime. To maintain the thermal power of the steam generator, therefore, its operating condition should be properly changed according to the degradation rate. Emphasis is given to the operation strategy of the steam generator to transport a constant thermal power regardless of the degradation rate. Comprehensive numerical solutions to the governing equations are acquired. It is found that a constant thermal power can be maintained by properly adjusting the secondary coolant outlet pressure with a variation of the superheat degree and secondary coolant pressure drop. A constant thermal power operation curve is obtained, and the thermal-hydraulic performance of the steam generator is analyzed according to the degradation rate in terms of the degree of superheat, secondary coolant pressure drop, temperature distribution, and quality distribution in the tube.
식생활 라이프스타일 그룹에 따른 소금관련 영양지식, 식태도, 식행동 비교 연구
윤혜려,강남이,김주현,Yoon, Hei-Ryeo,Kang, Nam-E,Kim, Juhyeon 한국식품조리과학회 2016 한국식품조리과학회지 Vol.32 No.3
Purpose: In this study, we comparatively investigated the nutrition knowledge, dietary attitude, and dietary behavior related to salt according to the types of dietary life style for differences between the groups. Methods: The survey was conducted between May 1 to July 31, 2014 among 500 adults aged >19 years in Seoul, Gyeonggi-do and Chungcheong-do areas. Results: Factor analysis of the dietary life style, indicated 4 factors including food convenience factor, food information emphasis factor, behavior factor of pursing food taste, and food purchase standard factor, which were classified into 3 groups according to differentiated dietary life style types; group 1 emphasized convenience and diversity of food, and price sensitiveness. and included subjects who had low interest in health and nutrition and were less likely to take care of their health through regular exercise,; group 2 emphasized food ingredients, food additives, usage and food purchase standards. and included subjects who were more likely to take care of their health through exercise and showed lower intake of fast food and less cases of eating out.; and group 3 showed relatively higher tendency toward dietary life style factors than the other two groups. The level of nutrition knowledge in sodium intake differed according to dietary life styles, and showed a significant difference in the dietary practice of sodium intake. Conclusion: Nutrition education on the healthy dietary habit of reducing sodium intake be based on ge and gender. In addition, an effort is required to improve behavior, interest, and attitude according to the important tendencies of the dietary life style.