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Kim, Yongchan,Woo, Sanghyun,Kim, Hyungchul,Lee, Jaesang,Kim, Honggyu,Lee, Hyerin,Jeon, Hyeongtag Cambridge University Press (Materials Research Soc 2010 Journal of materials research Vol.25 No.10
<P>The physical and electrical properties of La2O3 with and without an Al2O3 capping layer deposited by remote plasma atomic layer deposition were investigated. The electrical properties of the La2O3 films degraded due to the formation of lanthanum hydroxide after being exposed to air. The results of x-ray photoemission spectroscopy showed that the quantity of OH groups absorbed increased after exposure to air. For La2O3 with an Al2O3 capping layer, however, the electrical properties of the film did not change substantially because the capping layer effectively suppressed the formation of lanthanum hydroxide. The capacitance of the La2O3 decreased more than 30% after exposure to air, while La2O3 with an Al2O3 capping layer decreased by only about 4%. The <I>V</I>FB value of the La2O3 with an Al2O3 capping layer was near zero, and the hysteresis was about 120 mV. The leakage current densities of the film were maintained below 5 × 10<SUP>−7</SUP> A/cm<SUP>2</SUP> up to −15 MV/cm and the effective breakdown field was about −23.5 MV/cm.</P>
Kim, Dongwoo,Song, Kang Sub,Lim, Junyub,Kim, Yongchan Elsevier 2018 ENERGY Vol.155 No.-
<P><B>Abstract</B></P> <P>The objective of this study is to optimize the performance of a two-phase injection (TPI) heat pump considering annual performance factor (APF) and life cycle climate performance (LCCP). The performances of non-injection (NI), vapor injection (VI), and TPI heat pumps are measured under various outdoor temperatures. Based on the measured data, artificial neural network models for the NI, VI, and TPI heat pumps are developed to predict the performance indexes during cooling and heating seasons. As a result, the TPI heat pump shows higher heating capacity than the NI and VI heat pumps with a lower compressor discharge temperature in cold weather conditions. Therefore, the application of the TPI has a merit on reducing the size of the heat pump due to its lower back-up heater loss and over-capacity penalty. When the objective function maximizes the APF for system optimization in three climate regions, the TPI heat pump shows a 1.4–2.7% higher APF than the NI heat pump, and a 11.1%–18.1% smaller optimum rated heating capacity.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A TPI heat pump is investigated by considering APF and LCCP under various operating conditions. </LI> <LI> The TPI heat pump shows better performance than the NI and VI heat pumps at severe weather conditions. </LI> <LI> The TPI shows a merit on reducing the size of the heat pump due to its lower back-up heater loss and over-capacity penalty. </LI> <LI> The TPI heat pump exhibits higher annual performance, lower manufacturing cost, and lower environmental impact. </LI> </UL> </P>
Kim, Dongwoo,Chung, Hyun Joon,Jeon, Yongseok,Jang, Dong Soo,Kim, Yongchan Elsevier 2017 ENERGY Vol.135 No.-
<P><B>Abstract</B></P> <P>An analytical study is conducted to optimize the injection-port geometries of a vapor injection asymmetric scroll compressor operating under various climatic conditions. A numerical model was developed to predict the performance of the vapor injection asymmetric scroll compressor in the heating mode according to various operating parameters, and this numerical model was validated using data measured in a vapor injection heat pump. The effects of the location and number of injection ports on the performance of the asymmetric scroll compressor were analyzed using the numerical model. Both the optimal injection-port angle and required injection-port area increased as the outdoor temperature decreased in order to increase the injection mass flow rate. The optimized injection port designs were then proposed for the asymmetric scroll compressor in order to achieve the maximum SCOP (seasonal coefficient of performance) under various climatic conditions, improving the SCOP by 2%–6% relative to the baseline injection compressor.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A numerical model is developed to predict the performance of a vapor injection scroll compressor. </LI> <LI> The effects of the injection-port geometries on the performance of the heat pump are analyzed. </LI> <LI> The SCOPs of the heat pump with various injection-port designs are compared. </LI> <LI> The optimized injection-port designs are suggested under various climatic conditions. </LI> </UL> </P>
Yongchan Kim,Ho Seong Lee 대한설비공학회 2005 International Journal Of Air-Conditioning and Refr Vol.13 No.3
This paper reviews the literature on the performance of fin-and-tube heat exchangers under frosting and defrosting conditions. The effects of frosting and defrosting on the following parameters were discussed: frost growth, overall heat transfer coefficient, surface roughness, and surface characteristics on the heat exchanger. Comparisons of the experimental results and empirical correlations that were obtained from open literature were presented. In addition, a review of the defrosting methods was conducted.
Performance of a Two-Phase Injection Heat Pump with the Variation of Injection Quality and Pressure
Kim, Bo Gyeom,Kim, Dongwoo,Lee, Dongchan,Kim, Yongchan World Scientific Publishing Company 2017 International Journal of Air-Conditioning and Refr Vol.25 No.2
<P>Heat pumps are becoming more commonly and widely used due to their advantages in efficiency and versatile applications in both cooling and heating. However, the reliability of its compressor is being compromised due to high discharge temperatures caused by harsh operating conditions. Among the numerous studies conducted in improving the discharge temperature and performance of the heat pump, two-phase injection is receiving great interest. In this study, the performance of the two-phase injection heat pump was measured with a variation of operating parameters. The experiment results were used to study the performance change according to the operating parameter such as injection quality and pressure. It was found that the performance of the heat pump using the two-phase injection was better in terms of COP by up to 5.8% compared to that using the vapor injection. Furthermore, the two-phase injection was effective in reducing the discharge temperature to improve the compressor reliability. Two types of optimum injection qualities were suggested through this study: discharge temperature optimum injection quality (TIQ), and performance optimum injection quality (PIQ). It was found that in most conditions PIQ was sufficient in satisfying the compressor reliability, but in harsh operating conditions, where the compression ratio was high, TIQ was required in order to maintain the compressor reliability.</P>
Kim, Yongchan,Seo, Kook-Jeong,Lee, Kyu-Jung,Park, Youn cheol The Korean Society of Mechanical Engineers 2001 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.15 No.8
Evaporation heat transfer coefficients and pressure drops were measured for smooth and micro-fin tubes with R-22 and R-410A. Heat transfer measurements were performed for 3.0m long horizontal tubes with nominal outside diameters of 9.52 and 7.0mm over an evaporating temperature range of -15 to 5$\^{C}$, a mass flux range of 68 to 211kg/㎡s, and a heat flux range of 5 to 15kW/㎡. It was observed that the heat transfer coefficient increased with mass flux. Evaporation heat transfer coefficients of R-22 and R-410A increased as the evaporating temperature dropped at a lower heat flux. Generally, R-420A showed the higher heat transfer coefficients than R-22 in the range of low mass flux, high heat flux and high evaporating temperature. Pressure drop increased with a decrease of evaporating temperature and a rise of mass flux. Pressure drop of R-22 was higher than that of R-410A at the same mass flux.
An Algor ithm for Finding a Relationship Between Entities
Yongchan Kim(김용찬),Jinsoo Park(박진수),Jihae Suh(서지혜) 한국지능정보시스템학회 2018 지능정보연구 Vol.24 No.3
Database schema integration is a significant issue in information systems. Because schema integration is a time-consuming and labor-intensive task, many studies have attempted to automate it. Researchers typically use XML as the source schema and leave much of the work to be done through DBA intervention, e.g., there are various naming conflicts related to relationship names in schema integration. In the past, the DBA had to intervene to resolve the naming-conflict name. In this paper, we introduce an algorithm that automatically generates relationship names to resolve relationship name conflicts that occur during schema integration. This algorithm is based on an Internet collocation and English sentence example dictionary. The relationship between the two entities is generated by analyzing examples extracted based on dictionary data through natural language processing. By building a semi-automated schema integration system and testing this algorithm, we found that it showed about 90% accuracy. Using this algorithm, we can resolve the problems related to naming conflicts that occur at schema integration automatically without DBA intervention.