자동차 주유시 증발 가스 방출량 예측 연구

박재성,유홍선,손동연,김충익 중앙대학교 생산공학연구소 1998 생산공학연구소 논문집 Vol.7 No.1

자동차 주유시 대기중으로 빠져 나온 연료 증기는 환경을 오염시킨다. 주유시 연료증기 방출량을 최소화하기 위해서 ORVR 시스템이 적용된다. 그러나 이 시스템은 몇가지 어려운 기술적인 문제들이 존재한다. 본 연구에서는 주유 유량에 따른 연료 증기 방출량을 예측하였다. 이를 위하여 연료 탱크의 압력 변화, 연료 증기가 흡착되는 캐니스터로의 방출량을 시뮬레이션하였다. 연료 증기와 공기의 혼합 기체는 이상기체로 가정될 수 있다. 주유관을 흐르면서 액체 연료의 압력 강하는 유량과 주유관의 형상에 따라 각각 계산하였다. 압력 강하 검증을 위해서 직선관과 90도 곡관에 대해서 수행하였다. 또한 shut-off time을 예측하여 실험치와 비교를 하였다. 계산 결과 40 LPM 이하에서는 연료탱크가 가득 찰 때까지 주유가 되고, 이상에서는 매우 빠른 시간에 shut-off가 됨을 알 수 있었다. 더 나은 모델을 개발하기 위해서는 연료의 증발, 응축 그리고 연료 탱크내의 기체의 유동까지도 고려되어야 할 것이다. During the refueling process of automobiles, the fuel vapor escapes into the atmosphere and pollutes the environment. To reduce the fuel vapor emission during refueling, ORVR(Onboard Refueling Vapor Recovery) system is implemented. This system, however, needs to overcome several technical difficulties. This research studies the problem of the fuel vapor emission and the refueling flow rate in ORVR system. The pressure variation of the fuel tank during the refueling and the emission to the canister that absorbs the escaping fuel vapor are numerically simulated. The fuel-vapor and air mixture in gas phase is assumed to be ideal gas mixture. The pressure drop of liquid fuel through the refueling line is numerically calculated for various flow rates and shapes of the pipes. The results are verified for straight and 90 degree bend. The shut-off time is calculated and compared with experimental results. The flow rate of forty liter per minute is determined to be the critical refueling rate. Below 40 LPM the refueling process continues until the tank is filled, but above it the shut-off occurs at the early stages of refueling process. Experimental results and simulation results show good agreement. To improve the model, the transient evaporation and condensation are to be considered as well as the gaseous flow inside the tank.

Spin-orbit coupling induced band structure change and orbital character of epitaxialIrO2films

Kim, Woo Jin,Kim, So Yeun,Kim, Choong H.,Sohn, Chang Hee,Korneta, O. B.,Chae, Seung Chul,Noh, Tae Won American Physical Society 2016 Physical Review B Vol.93 No.4

A spin-dependent local moment approach to the Anderson impurity model

Kim, Choong H,Yu, Jaejun IOP Pub 2007 Journal of physics, an Institute of Physics journa Vol.19 No.45

<P>We present an extension of the local moment approach to the Anderson impurity model with spin-dependent hybridization. By employing the two-self-energy description, as originally proposed by Logan and co-workers, we applied the symmetry restoration condition for the case with spin-dependent hybridization. Self-consistent ground states were determined through variational minimization of the ground state energy. The results obtained with our spin-dependent local moment approach applied to a quantum dot system coupled to ferromagnetic leads are in good agreement with those obtained from previous work using numerical renormalization group calculations.</P>

Spin and orbital angular momentum structure of Cu(111) and Au(111) surface states

Kim, Beomyoung,Kim, Choong H.,Kim, Panjin,Jung, Wonsig,Kim, Yeongkwan,Koh, Yoonyoung,Arita, Masashi,Shimada, Kenya,Namatame, Hirofumi,Taniguchi, Masaki,Yu, Jaejun,Kim, Changyoung American Physical Society 2012 Physical review. B, Condensed matter and materials Vol.85 No.19

Manipulation of electronic structure via alteration of local orbital environment in [(SrIrO3)m,(SrTiO3)](m=1,2,and∞) superlattices

Kim, So Yeun,Kim, Choong H.,Sandilands, L. J.,Sohn, C. H.,Matsuno, J.,Takagi, H.,Kim, K. W.,Lee, Y. S.,Moon, S. J.,Noh, T. W. American Physical Society 2016 Physical Review B Vol.94 No.24

<P>We investigated the electronic structure of [(SrIrO3)(m),(SrTiO3)](m = 1, 2, and infinity) superlattice (SL) thin films with optical spectroscopy and first principles calculations. Our optical results confirmed the existence of the J(eff) = 1/2 states in SL samples, similar to the bulk Ruddlesden-Popper series Sr Ir-n+ 1(n) O3n+1 iridates. Apart from this similarity, in the SL samples, we observed red shifts of the characteristic optical excitations in the J(eff) = 1/2 state and an enhancement of the low-energy spectral weight, which implies a reduction in the effective electron correlation for bands near the Fermi energy. The density functional theory plus Coulomb interactions (DFT + U) calculations suggested that the SrTiO3 layer intervened between SrIrO3 layers in the SLs activated additional hopping channels between the Ir ions, thus increasing the bandwidth and reducing the effective strength of the correlations. This paper demonstrates that fabrication of iridium-based heterostructures can be used to finely tune electronic structures via alteration of their local orbital environments.</P>

Topological quantum phase transitions driven by external electric fields in Sb2Te3 thin films.

Kim, Minsung,Kim, Choong H,Kim, Heung-Sik,Ihm, Jisoon National Academy of Sciences 2012 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.109 No.3

<P>Using first-principles calculations, we show that topological quantum phase transitions are driven by external electric fields in thin films of Sb(2)Te(3). The film, as the applied electric field normal to its surface increases, is transformed from a normal insulator to a topological insulator or vice versa depending on the film thickness. We identify the band topology by directly calculating the Z(2) invariant from electronic wave functions. The dispersion of edge states is also found to be consistent with the bulk band topology in view of the bulk-boundary correspondence. We present possible applications of the topological phase transition as an on/off switch of the topologically protected edge states in nano-scale devices.</P>

Interplay between local electron correlation and Janh-Teller electron-phonon interaction

Kim, Choong H.,Lee, Hyun C. American Physical Society 2006 Physical review. B, Condensed matter and materials Vol.73 No.11

Combined Effects of Nano-Hydroxyapatite and NaF on Remineralization of Early Caries Lesion

Kim, M.Y.,Kwon, H.K.,Choi, Choong Ho,Kim, B.I. Trans Tech Publications, Ltd. 2007 Key Engineering Materials Vol.330-332 No.1

<P>A previous study reported that many supplements have been added to NaF mouthrinses to improve the remineralization potential. Nano-hydroxyapatite (nano-HA) might also be suitable to this purpose because these nano-size particles can penetrate the enamel pores. Moreover, hydroxyapatite is similar to the inorganic component of teeth and is both bioactive and biocompatible. The aim of this study was to evaluate the combined effects of a nano-HA and fluoride mouthrinse on an early caries lesion in human enamel using an in vitro cycle remineralization and treatment model. Forty-eight human enamel specimens, which had a Vickers Hardness Number (VHN) of 25~45 were artificially demineralized for 48h. There were 8 treatment groups (0%, 1%, 5%, 10% nano-HA in distilled water and the same concentrations of nano-HA in a 0.05% NaF solution). The specimens were incubated in an in vitro remineralization model. After immersing the specimens into the treatment and remineralization solution for 12 hours each, the VHN of each specimen was evaluated for total 24 hours. This step was repeated once again for total 48 hours. The enamel surfaces of all specimens were examined by Confocal Laser Scanning Microscopy (CLSM) and SEM. The statistical significance of the data was identified by one-way ANOVA followed by a Duncan’s studentized range test. A p value < 0.05 was considered significant. The results showed that the degree of remineralization, as revealed by the VHN values, was higher in the NaF groups than in the distilled water groups. The VHNs of the remineralized enamel specimens for 48 hours were higher than after the 24 hours treatment. In addition, the level of remineralization increased with increasing concentration of nano-HA and was more pronounced in the NaF groups than the distilled water groups (p<0.05). The CLSM and SEM images nano-sized particles attached to the enamel in the nano-HA treated groups. Nano-HA might play a synergistic role in remineralization with a fluoride mouthrinse. However, more study will be needed to determine the optimal condition of nano-HA and NaF mouthrinse for human use. In conclusion, nano-HA in a 0.05% NaF mouthrinse can help remineralize an early caries lesion.</P>

이차전지용 급속 충전 시스템의 해석 및 설계

반충환(Choong-Hwan Ban),이영진(Y.J. Lee),한동화(D.H. Han),권완성(W.S. Kwon),김기환(K.H. Kim),은종목,최규하(G.H. Choe) 제어로봇시스템학회 2012 제어로봇시스템학회 합동학술대회 논문집 Vol.2012 No.7

본 논문에서는 기존의 풀브리지 컨버터를 적용한 50kW 급속 충전 시스템을 구성하였을 경우에 발생하는 스위칭 손실과, 대전류로 인한 발열과 내부 소자 파괴 등을 방지하기 위해 풀브리지 컨버터 모듈을 두 개의 모듈로 구성하여 SISO 풀브리지 컨버터로 설계하여 제작하였으며, 배터리는 코캄社의 리튬 폴리머 배터리(444[V], 40[Ah])를 사용하였다.

Remineralization Potential of Sports Drink Containing Nano-Sized Hydroxyapatite

Lee, H.J.,Min, J.H.,Choi, Choong Ho,Kwon, H.G.,Kim, B.I. Trans Tech Publications, Ltd. 2007 Key Engineering Materials Vol.330-332 No.1

<P>Several studies have reported the on dental erosive potential of sports drinks with a low pH. Therefore, there is a need for new components that can reduce the erosive potential of a sports drink. Hydroxyapatites (HA) are the major components of dental enamel and bone mineral as biological apatites. In addition, HA contains a significant amount of calcium and phosphate, which can promote remineralization. Hence, some remineralization of the enamel surface can be expected if nano-sized hydroxyapatite (nano-HA) is added to a sports drink. The aim of this study was to evaluate the remineralization effects of sports drinks containing nano-HA in vitro. The crowns of extracted human molars were embedded in acrylic resin and then ground flat and polished. A commercially available sports drink (Powerade, Coca-Cola, South Korea) was purchased from a local supermarket. Nano-HA was added at a concentration of 0.05%, 0.25%, and 0.5%. Deionized water (DW) was used as the negative control. The pH of each solution was measured by a pH-meter at room temperature. The enamel specimens were immersed in each solution for 15 and 30 minutes at 37°C. In order to evaluate remineralization effect, the VHN of the enamel surface was measured at every step by microhardness test (JTTOSHI INC, Japan). CLSM and SEM were utilized to identify the change of enamel surface. The pH of test solutions and VHN of enamel surface increased in proportion to the nano-HA concentrations (P<0.05). The nano-HA could reduce the erosive potential of a sports drink in a concentration dependent manner. These effects were confirmed by the CLSM and SEM images, which showed the remineralization effect of nano-HA. However, more study will be needed to examine the optimal concentration and remineralization mechanism of the nano-HA in sports drinks. In conclusion, the addition of nano-HA to a sports drink can promote enamel remineralization.</P>