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Convective heat transfer characteristics of nanofluids under laminar and turbulent flow conditions
Younghwan Kwon,Yonghyeon Cho,Chengguo Li,Seongir Cheong,Yujin Hwang,Jaekeun Lee,Daeseung Hong,Seongyong Moonb 한국물리학회 2009 Current Applied Physics Vol.9 No.2
To investigate the effect of nanofluids on convective heat transfer, an experimental study was performed through a circular straight tube with a constant heat flux condition in the laminar and turbulent flow regime. Stable nanofluids, which were water-based suspensions of alumina and amorphous carbonic nanoparticles, were prepared by two- and one-step methods. The effects of thermal conductivity and supernatant nanoparticles of the nanofluids on convective heat transfer were investigated under different flow regimes. In alumina nanofluids containing 3 vol% of suspended particles, the increment of thermal conductivity and convective heat transfer coefficient was 8% and 20%, respectively. For amorphous carbonic nanofluids, the thermal conductivity was similar to that of water, and the convective heat transfer coefficient increased by only 8% in laminar flow. In a comparison of thermal conductivity and convection, the enhancement of the convective heat transfer was much higher than that of the thermal conductivity of nanofluids. The movements of nanoparticles enhanced the convective heat transfer at the entrance region. To investigate the effect of nanofluids on convective heat transfer, an experimental study was performed through a circular straight tube with a constant heat flux condition in the laminar and turbulent flow regime. Stable nanofluids, which were water-based suspensions of alumina and amorphous carbonic nanoparticles, were prepared by two- and one-step methods. The effects of thermal conductivity and supernatant nanoparticles of the nanofluids on convective heat transfer were investigated under different flow regimes. In alumina nanofluids containing 3 vol% of suspended particles, the increment of thermal conductivity and convective heat transfer coefficient was 8% and 20%, respectively. For amorphous carbonic nanofluids, the thermal conductivity was similar to that of water, and the convective heat transfer coefficient increased by only 8% in laminar flow. In a comparison of thermal conductivity and convection, the enhancement of the convective heat transfer was much higher than that of the thermal conductivity of nanofluids. The movements of nanoparticles enhanced the convective heat transfer at the entrance region.
Effect of materials structure and composition on properties of siloxane-containing hydrogels
Younghwan Kwon,Minhyeon Song,Yong Gu Hwang,Seung Hyun Chang,Won Ji Hong 한국물리학회 2008 Current Applied Physics Vol.8 No.3,4
Properties of siloxane-containing hydrogels were investigated with formulations of siloxane-containing monomer (TRIS) and/or poly(dimethylsiloxane) macromers with hydrophilic monomers such as 2-hydroxyethyl methacrylate (HEMA) and N,N-dimethyl acrylamide (DMA). Phase separation behavior of siloxane-containing hydrogels was found to be affected mainly by compositions of siloxanebased hydrophobic/hydrophilic monomers. Properties of siloxane-containing hydrogels were investigated with formulations of siloxane-containing monomer (TRIS) and/or poly(dimethylsiloxane) macromers with hydrophilic monomers such as 2-hydroxyethyl methacrylate (HEMA) and N,N-dimethyl acrylamide (DMA). Phase separation behavior of siloxane-containing hydrogels was found to be affected mainly by compositions of siloxanebased hydrophobic/hydrophilic monomers.
YoungHwan Kwon,Min-Gon Kim,Seong Gon Choi,Jun Kyun Choi IEEE 2011 IEEE COMMUNICATIONS LETTERS Vol.15 No.9
<P>Based on the combination of an EPON and various last-mile connections, EPON-based access networks can provide broadband access services economically. It, however, is imperative to create an optimized multicast retransmission policy in consideration of such a combined architecture. To resolve this issue, this letter proposes a new Centralized Selective Multicast Retransmission Policy (CSMRP) that efficiently retransmits multicast traffic. Performance results show that the proposed CSMRP can effectively reduce bandwidth consumption and queuing delay for enhanced resource efficiency.</P>
KWON, YoungHwan,KIM, Min-Gon,CHOI, Seong Gon,CHOI, Jun Kyun The Institute of Electronics, Information and Comm 2010 IEICE TRANSACTIONS ON COMMUNICATIONS - Vol.93 No.1
<P>This letter proposes a new multicast traffic control policy in TDM-PON, which differentially classifies multicast flows which have relatively many associated receivers as high-class, and multicast flows which have relatively few associated receivers as low-class. Simulation results confirm that the proposed policy can effectively enhance multicast performance regarding delay and loss, specifically important to multimedia services, compared to the legacy policy.</P>
A Multicast Queuing Mechanism for Layered Multicast in Heterogeneous Environments
YoungHwan Kwon,Seong Gon Choi,Jun Kyun Choi 대한전자공학회 2007 ITC-CSCC :International Technical Conference on Ci Vol.2007 No.7
Layered multicast delivers multi-rate data to support heterogenous environments in a multicast service. In layered multicast, each layer has different delay according to the number of receivers. Therefore, we propose a multicast queuing mechanim for layered multicast in heterogeneous environments to reduce the delay variance among layers.
A Weighted Scheduling Mechanism to Reduce Multicast Packet Loss in IPTV Service over EPON
YoungHwan Kwon,최준균,최성곤,엄태원,종상국 한국전자통신연구원 2009 ETRI Journal Vol.31 No.4
This letter proposes a weighted scheduling mechanism for Internet protocol television (IPTV) to improve the loss performance of multicast transmission over an Ethernet passive optical network (EPON). We propose a new weight policy from the number of multicast receivers to proportionally allocate the downstream bandwidth of IPTV traffic. The proposed mechanism is used in an optical line terminal to decrease lost packets of favorite IPTV services because the lost multicast packets are proportional to the number of receivers. The total proportion of lost multicast packets is reduced by up to 73% in an EPON.
Kwon, Hyeokmin,Joo, Younghwan,Kim, Sung Jin Elsevier 2018 Energy conversion and management Vol.156 No.-
<P><B>Abstract</B></P> <P>In this study, horizontally oriented radial plate-fin heat sinks in natural convection are optimized analytically and experimentally. The thermal resistance is selected as an objective function under the constraint of a given base-to-ambient temperature difference. For thermal optimization, a new correlation of the heat transfer coefficient for the radial plate-fin heat sinks is developed using the asymptotic method and validated experimentally. While the existing correlation has a limited applicable range, the newly developed correlation covers complete ranges of the three design parameters for a fin geometry: fin thickness (<I>t</I>), fin length (<I>L</I>), and number of fins (<I>n</I> <SUB>fin</SUB>). Using this new correlation, the thermal performance of a radial plate-fin heat sink is optimized with respect to these three design parameters. Finally, optimum fin geometries for applications with various sizes are obtained, since the newly suggested correlation is applicable to various physical sizes which are characterized by the base diameter (<I>D</I>) and the fin height (<I>H</I>).</P> <P><B>Highlights</B></P> <P> <UL> <LI> A new analytic model for radial plate-fin heat sinks is developed. </LI> <LI> Experimental and numerical study are performed for the validation of the model. </LI> <LI> The fin geometry is optimized at various physical sizes. </LI> </UL> </P>