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161.
Nucleate boiling heat transfer for refrigerants, R113, and R113+ wt4% ethanol mixture, an azeotropic mixture under electric
field was investigated experimentally in a single-tube shell/ tube heat exchanger. A special electrode configuration which
provides a more uniform electric field that produces more higher voltage limit against the dielectric breakdown was used in
this study. Experimental study has revealed that the electrical charge relaxation time is an important parameter for the boiling
heat transfer enhancement under electric field. Up to 1210% enhancement of boiling heat transfer was obtained for R113+wt4%
ethanol mixture which has the electrical charge relaxation time of 0.0053 sec whereas only 280% enhancement obtained for R113
which has relaxation time of 0.97 sec. With artificially machined boiling surface, more enhancement in the heat transfer coefficient
in the azeotropic mixture was obtained. 相似文献
162.
Yang -Hann Kim Soo Hyun Kim Byoung Duk Lim Yoon Keun Kwak 《Journal of Mechanical Science and Technology》1988,2(2):125-132
For the measurement of transmission loss of the silencers which have mean flow, the noise levels of signals depicted by microphone
usually prohibit accurate measurements of the transmission loss. To overcome this difficulty, static pressure compensation
technique has been developed to increase the dynamic range of the microphones, resulting accurate measurement of transmission
loss in the presence of high noise level. Series of experiments to investigate the acoustic characteristics of expansion chamber
with mean flow has been performed using the pressure compensated microphones. Results demonstrate: (1) frequency shift due
to the presence of mean flow, (2) effect of length, diameter, offset length and twisting angles to the transmission loss of
expansion chamber with and without mean flow (up to 50m/sec), (3) relation between the proposed parameter ‘aspect ratio’ and
number of peaks of transmission loss in low frequency region. 相似文献
163.
Jaehyun Park Se Hun Joo Yoon‐Jeong Kim Ju Hyun Park Sang Kyu Kwak Seokhoon Ahn Seok Ju Kang 《Advanced functional materials》2019,29(32)
In this work, a highly conductive organic cocrystal is investigated as an anode material for conducting agent‐free lithium‐ion battery (LIB) electrodes. A unique morphology of semiconducting fullerene (C60) and contorted hexabenzocoronene (cHBC) is developed as a cocrystal that efficiently enhances the electron transfer during discharge and charge processes due to the formation of a well‐defined junction between C60 and cHBC. In particular, the present study reveals the exact cocrystal phase of orthorhombic Pnnm using grazing incidence X‐ray diffraction characterization and computational methods. The detailed cocrystal structure analysis indicates that the columnar structure of C60/cHBC cocrystal facilitates the reliable vacant sites for Li+ storage, which ultimately enhances the reversible capacity to 330 mAh g–1 at 0.1 A g–1 with long cyclability of 600 cycles in the absence of a conducting agent. Furthermore, the rate performance of the C60/cHBC cocrystal anode is improved compared to that of the graphite anode, indicating that the cocrystal formation between C60 and cHBC enhances the charge transport at a high current density. It demonstrates that the approach of this study can be a promising strategy for preparing conducting agent‐free organic cocrystal anodes, which also provides a viable design rule for high‐performance LIBs electrodes. 相似文献
164.
165.
Jinsung Kwak Se‐Yang Kim Yongsu Jo Na Yeon Kim Sung Youb Kim Zonghoon Lee Soon‐Yong Kwon 《Advanced materials (Deerfield Beach, Fla.)》2018,30(30)
Graphene has recently attracted particular interest as a flexible barrier film preventing permeation of gases and moistures. However, it has been proved to be exceptionally challenging to develop large‐scale graphene films with little oxygen and moisture permeation suitable for industrial uses, mainly due to the presence of nanometer‐sized defects of obscure origins. Here, the origins of water permeable routes on graphene‐coated Cu foils are investigated by observing the micrometer‐sized rusts in the underlying Cu substrates, and a site‐selective passivation method of the nanometer‐sized routes is devised. It is revealed that nanometer‐sized holes or cracks are primarily concentrated on graphene wrinkles rather than on other structural imperfections, resulting in severe degradation of its water impermeability. They are found to be predominantly induced by the delamination of graphene bound to Cu as a release of thermal stress during the cooling stage after graphene growth, especially at the intersection of the Cu step edges and wrinkles owing to their higher adhesion energy. Furthermore, the investigated routes are site‐selectively passivated by an electron‐beam‐induced amorphous carbon layer, thus a substantial improvement in water impermeability is achieved. This approach is likely to be extended for offering novel barrier properties in flexible films based on graphene and on other atomic crystals. 相似文献
166.
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168.
Byeon Yeong-Hyeon Lee Myung-Won Lee Jae-Neung Kwak Keun-Chang 《International Journal of Control, Automation and Systems》2018,16(1):368-376
International Journal of Control, Automation and Systems - In this study, an intelligent predictor is designed for predicting the direction of dinghy booms and coaching dinghy sailing using the... 相似文献
169.
Kyungwoo Kang Myungjae Kwak Seung Kyoon Shin 《Journal of Computer Information Systems》2018,58(2):110-121
This study investigates the underlying motivational factors of knowledge exchange intentions (intention to obtain and to provide knowledge) within virtual community contexts. Perceived virtual network structures, namely virtual network connectivity (CN) and virtual network closeness (CL), are suggested as the important antecedents of knowledge sharing intentions in the context of virtual knowledge exchange communities. Anonymity (AN), one of the unique characteristics of virtual communities, but controversial due to its multi-faceted effects, is considered in a structural model as a factor having an impact on a virtual network structure. Data collected from participants of virtual communities through online surveys are analyzed using Partial Least Squares (PLS) structural equation modeling (SEM) to empirically test the proposed hypotheses. The results reveal that both CN and CL have a significant impact on both of the knowledge exchange intentions although CL shows an opposite direction of the impact. The results also show that AN has a significant impact on CL as expected but not on CN. Implications of this study may shed some light on better understanding community participants’ intentions to obtain and provide knowledge, along with the impact of anonymity on the perceived network structure. 相似文献
170.
Won-Jin Kwak Hyung-Seok Lim Peiyuan Gao Ruozhu Feng Sujong Chae Lirong Zhong Jeffrey Read Mark H. Engelhard Wu Xu Ji-Guang Zhang 《Advanced functional materials》2021,31(2):2002927
A stable electrolyte is critical for practical application of lithium–oxygen batteries (LOBs). Although the ionic conductivity and electrochemical stability of the electrolytes have been extensively investigated before, their oxygen solubility, viscosity, volatility, and the stability against singlet oxygen (1O2) still need to be comprehensively investigated to provide a full picture of the electrolytes, especially for an open system such as LOBs. Herein, a systematic investigation is reported on the localized high-concentration electrolytes (LHCEs) using different fluorinated diluents in comparison with those of conventional electrolytes. The physical properties and activation energies for reactions with singlet oxygen (1O2) of these electrolytes are calculated by density functional theory. The electrochemical performances of LOBs using these electrolytes are compared. This study reveals that the correlation between the stability of the electrolytes and their physical and electrochemical properties depends strongly on the diluents in LHCEs. Therefore, it shines light on the rational design of new electrolytes for LOBs. 相似文献