Natural convection heat transfer characteristics in vertical cavities with active and inactive top and bottom disks

Kang, Gyeong-Uk,Chung, Bum-Jin Elsevier 2015 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.87 No.-

<P><B>Abstract</B></P> <P>Natural convection heat transfer was investigated in vertical cavities where either all surfaces were active, or only the vertical surface was active for four different geometries, which were varied by placing a disk at the top and/or bottom of the cavity. A cupric acid–copper sulfate electroplating system was employed for mass transfer experiments exploiting the analogy with heat transfer. The Rayleigh number was varied in the range 4.55×10<SUP>9</SUP> ⩽ <I>Ra<SUB>Lw</SUB> </I> ⩽3.79×10<SUP>13</SUP>. Preliminary tests for a vertical pipe, upward- and downward-facing horizontal disks showed good agreement with existing correlations. The measured Nusselt numbers in the vertical cavities with all surfaces active were always greater than those with only the vertical surface active, which is attributed to greater hydrodynamic interaction of the flows generated by different surfaces. When all surfaces were active, the bottom-closed cavity exhibited the largest heat transfer rates, followed by both-closed, top-closed, and both ends open cavities; this trend was observed with laminar and turbulent flows. With only the vertical surface active, similar trends were observed except that the heat transfer rates were almost identical for both-open and top-closed cavities, which is attributed to the weak influence of the top disk on the heat transfer characteristics. Using these results, empirical correlations were derived for both laminar and turbulent flow conditions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Natural convection inside a vertical pipe with/without top and bottom lids. </LI> <LI> A comprehensive review of the literature was made. </LI> <LI> It covers laminar and turbulent flows and either active or inactive top and bottom lids. </LI> <LI> Phenomenological explanation including the secondary flows was discussed. </LI> <LI> Heat transfer correlations were derived and proposed. </LI> </UL> </P>

Influence of the height-to-diameter ratio on turbulent mixed convection in vertical cylinders

Kang, Gyeong-Uk,Chung, Bum-Jin Springer-Verlag 2012 Heat and mass transfer Vol.48 No.7

Natural convection heat transfer on a vertical cylinder submerged in fluids having high Prandtl number

Kang, Gyeong-Uk,Chung, Bum-Jin,Kim, Hyoung-Jin Elsevier 2014 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.79 No.-

<P><B>Abstract</B></P> <P>Natural convection experiments on both vertical thin- and thick-cylinders were performed for Rayleigh numbers from 1.4×10<SUP>9</SUP> to 3.2×10<SUP>13</SUP>, the <I>H</I>/<I>D<SUB>O</SUB> </I> from 0.6 to 140 at high Prandtl numbers. A sulfuric acid–copper sulfate electroplating system based on analogy concepts were employed for the measurements of heat transfer rates. For vertical thin-cylinders, Nusselt numbers were in satisfactory agreements with the existing correlation on vertical plates. Especially, those measured at the high <I>H</I>/<I>D<SUB>O</SUB> </I> were higher even though the thermal boundary layer is much thinner than the cylinder diameter. This was due to the flow interactions, which promoted the development of momentum boundary layer and velocity fluctuations, leading to the enhancement of the Nusselt number. For vertical thick-cylinders, Nusselt numbers in laminar flows were in satisfactory with the existing correlations. However, those in turbulent flows decreased as Prandtl number increased in this study. Its phenomena are caused by the formation of very thin thermal boundary layer within viscous sublayer by very high Prandtl number. In this case, the velocity within thermal boundary layer becomes very low by no-slip condition near the heated wall and the heat is transferred by conduction rather than advection. Based upon the results, empirical correlations on vertical thick-cylinders were derived for laminar and turbulent flows.</P>

Best Practice Guidelines for the Use of CFD in Dry Cask Applications of US NRC

Gyeong-Uk Kang,Dae-Sik Yook,Jung-Hoon Cha 한국방사성폐기물학회 2018 한국방사성폐기물학회 학술논문요약집 Vol.2018 No.10

수직 원형관내 혼합대류 유동영역지도의 유효성 검토

강경욱(Gyeong-Uk Kang),김형진(Hyoung-Jin Kim),윤시태(Si-Tae Yoon),정범진(Bum-Jin Chung) 한국에너지학회 2014 에너지공학 Vol.23 No.3

높은 Pr 수의 유체를 사용한 수직 원형관 외부의 자연대류 실험

강경욱(Gyeong-Uk Kang),정범진(Bum-lin Chung) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.5

수직 원형관 외부의 자연대류는 많은 실용적인 관심의 대상이 되고 있으며 곡률효과에 대한 이론과 열전달상관식은 교과서에도 잘 정리되어 있다. 본 연구에서는 유사성 원리를 이용하여 매우 높은 Pr 수의 유체를 사용하여 수직 원형관 외부의 자연대류 열전달 현상을 실험적으로 연구하였다. 황산-황산구리 수용액의 전기도금계를 물질전달계로 채택하였으며, 실험은 직경 0.005m~0.035m의 음극을 사용하여 Pr 수 2,094~4,173 그리고 Gr<SUB>H</SUB> 수 5.2×10?~1.0×10¹?에서 열전달계수를 측정하였다. 실험을 통하여 도출한 충류 상관식은 NU<SUB>H</SUB> = 0.55Ra<SUB>H</SUB><SUP>0.25</SUP>, 난류 상관식은 Nu<SUB>H</SUB> = 0.12Ra<SUB>H</SUB><SUP>0.28</SUP>Pr<SUP>0.1</SUP>였다. 충류에서 실험한 결과는 King, Jakob와 Linke, McAdams, Bottemanne의 수직 원형관 자연대류의 열전달 상관식에 일치하였다. 그러나 난류에서는 McAdams의 상관식과 일치하지 않았고 수직평판 난류 자연대류 상관식인 Fouad의 상관식과 일치하였고 Pr 수에 대한 의존성이 나타났다. 그 원인은 높은 Pr 수에 따라서 열경계층 두께가 관의 직경보다 매우 얇았기 때문인 것으로 판단된다. Natural convection on the outer surface of a vertical pipe has drawn research interests for many practical purposes and well established theories on the curvature effect and heat transfer correlations are available in textbooks. This study investigated the phenomena using mass transfer experiments with high Pr number using the analogy concept. A cupric acid-copper sulfate electroplating system was adopted as the mass transfer system. Tests were performed for Gr<SUB>H</SUB> numbers from 5.2×10? to 1.0×10¹?, Pr numbers from 2,094 to 4,173, and the diameters from 0.005m to 0.035m. The obtained correlations were NU<SUB>H</SUB> = 0.55Ra<SUB>H</SUB><SUP>0.25</SUP> for laminar and Nu<SUB>H</SUB> = 0.12Ra<SUB>H</SUB><SUP>0.28</SUP>Pr<SUP>0.1</SUP> for turbulent. The test results for laminar flow conditions agreed well with the correlations of King, Jakob & Linke, McAdam, and Bottemanne. However, for turbulent conditions, the test results show discrepancy with the correlation of McAdams developed for vertical pipe geometry but instead they showed agreement with the heat transfer correlations of Fouad developed for a vertical plate and also show the dependence on Pr numbers. The very thin thermal boundary layer compared to the diameter of the pipe due to the high value of Pr number seems to make the curvature effect negligible.

수직 원형관 내부에서 발생하는 자연대류 열전달에서 상·하단 마개의 영향

강경욱(Gyeong-Uk Kang),정범진(Bum-Jin Chung) 한국에너지학회 2011 에너지공학 Vol.20 No.3

높은 Pr 수의 유체를 사용한 수직 원형관 외부의 자연대류 실험

강경욱(Gyeong-Uk Kang),정범진(Bum-Jin Chung) 대한기계학회 2011 大韓機械學會論文集B Vol.35 No.1

유사성 원리를 이용하여 매우 높은 Pr 수의 유체를 사용하여 수직 원형관 외부의 자연대류 열전달 현상을 실험적으로 연구하였다. 황산-황산구리 수용액의 전기도금계를 물질전달계로 채택하였으며, 실험은 직경 0.005m~0.035m의 음극을 사용하여 Pr 수 그리고 2,094~4,173 RaH 수 1.4×10?~4×10₁₃에서 열전달계수를 측정하였다. 층류에서 실험한 결과는 King, Jakob와 Linke, McAdams, Bottemanne의 수직원형관 자연대류의 열전달 상관식에 일치하였고 난류에서는 수직평판 난류 자연대류 상관식인 Fouad의 상관식과 일치하였고 Pr 수에 대한 의존성이 나타났다. 실험을 통하여 도출한 층류 상관식은 NuH=0.55Ra<SUP>0.25</SUP>H, 난류 상관식은 NuH=0.12Ra<SUP>0.28</SUP>HPr<SUP>0.1</SUP>였다. 층류와 난류사이의 천이는 . RaH 수 약 10¹²에서 발생하였다. In this study, we investigated the natural convection on the outer surface of a vertical pipe by performing mass transfer experiments using fluids with high Pr number using the concept of analogy between heat and mass transfer. A cupric acid-copper sulfate electroplating system was adopted as the mass transfer system. Tests were performed for RaH numbers from 1.4×10? to 4×10¹³, Pr numbers from 2,094 to 4,173, and diameters from 0.005 m to 0.035 m. The test results for laminar flow conditions were in good agreement with the correlations reported by King, Jakob and Linke, McAdam, and Bottemanne, and those for turbulent conditions with the correlations presented by Fouad for a vertical plate and also proved the dependence on Pr numbers. The obtained correlations were NuH=0.55Ra<SUP>0.25</SUP>H for laminar and NuH = 0.12Ra<SUP>0.28</SUP>HPr<SUP>0.1</SUP> for turbulent. The transition between laminar and turbulent occurs at RaH of about 10¹².

Pathogen Surveillance of Acute Respiratory Infection in Chungcheongnam-do, 2019-2020

Kang Bum LEE,Jong jin PARK,Dong Uk KIM,Han Na KIM,Do Gyeong KWON,Soo Young LEE,Bum Ju SEO,Han Na JEON,Mi Na PARK,Woo Sik KIM 한국생물공학회 2020 한국생물공학회 학술대회 Vol.2020 No.10

Selective Synthesis of a New Macropolycycle Containing One N-CH₂-N Linkage and Its Reaction with Cu²⁺ and Ni²⁺ Ions in Methanol

Kang, Shin-Geol,Kweon, Jae-Keun,Jeong, Gyeong-Rok,Lee, Uk Korean Chemical Society 2008 Bulletin of the Korean Chemical Society Vol.29 No.10

The reaction of 3,14-dimethyl-2,6,13,17-tetraazatetracyclo[16.4.0$0^{1.18}.0^{7.12}$]docosane ($L^1$) with formaldehyde in warm methanol yielded 3,14-dimethyl-2,6,13,17-tetraazatetracyclo[16.4.$1^{2.6}.0^{1.18}.0^{7.12}$]tricosane ($L^7$) containing one 1,3-diazacyclohexane subunit. In methanol, $L^7$ readily reacts with $Cu^{2+}$ ion to form [$CuL^7(H_2O)$]$^{2+}$ which is extremely inert against methanolysis. In the solution containing $Ni^{2+}$ ion, however, $L^7$ reacts with methanol to yield [$NiL^3$]$^{2+}$ ($L^3$ = 2-(methoxymethyl)-5,16-dimethyl-2,6,13,17-tetraazatricyclo[16.4.$0^{1.18}.0^{7.12}$]- docosane), in which one N-$CH_2OCH_3$ pendant arm is appended. The copper(II) complex [$CuL^7(H_2O)$]- $(ClO_4)_2{\cdot}3H_2O\;(I{\cdot}3H_2O)$ has a severely distorted trigonal bipyramidal coordination geometry with a 4-5- 6-5 chelate ring sequence. The crystal structure of [$NiL^3$]$(PF_6)_2{\cdot}2H_2O$ (IIb) shows that the N-$CH_2OCH_3$ pendant arm is not coordinated to the metal ion in the solid state. In various solvents (S), however, the nickel(II) complex exists as a mixture of [$NiL^3$(S)]$^{2+}$, in which the N-$CH_2OCH_3$ group as well as S is coordinated to the metal ion, and [$NiL^3$]^{2+}.