Effect of sintered microporous coating at the evaporator on the thermal performance of a two-phase closed thermosyphon

Kim, Yeonghwan,Shin, Dong Hwan,Kim, Jin Sub,You, Seung M.,Lee, Jungho Elsevier 2019 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.131 No.-

<P><B>Abstract</B></P> <P>In this study, the effects of sintered microporous coating at the evaporator on the thermal performance of a two-phase closed thermosyphon (TPCT) are experimentally investigated using distilled water as a working fluid. The TPCT comprises evaporator, adiabatic, and condenser sections, which have an inner diameter of 25 mm and lengths of 300, 300, and 325 mm, respectively. Copper microparticles are sintered on the inner surface of the evaporator to form a 500-μm-thick microporous structure. Boiling and condensation heat transfer coefficients on the microporous coated TPCT are obtained at filling ratios (FRs) ranging from 0.25 to 1.0 and inclination angles ranging from 90° to 5°. The boiling heat transfer coefficient at the microporous coated evaporator is enhanced owing to an increase in the number of nucleation sites and thin film evaporation in the liquid film formed by capillary force through the porous structure, especially at a low FR. The condensation heat transfer is also affected by the microporous coated evaporator due to the increased amount of vapor generation at the low FR. The overall thermal resistance of the microporous coated TPCT is reduced by 51% at an FR of 0.35 and 30% at an FR of 0.75. The TPCT used in this study shows the best thermal performance at inclination angles between 15° and 30° and FRs between 0.2 and 0.4.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Boiling heat transfer in the thermosyphon is enhanced on the microporous coated surface. </LI> <LI> Condensation heat transfer performance is also affected by the microporous coating. </LI> <LI> The overall thermal resistance is reduced up to 51% through the microporous coating. </LI> </UL> </P>

A REVIEW OF ENHANCEMENT OF BOILING HEAT TRANSFER THROUGH NANOFLUIDS AND NANOPARTICLE COATINGS

You, Seung-M.,Amaya, Miguel,Kwark, Sang-M. The Society of Air-Conditioning and Refrigerating 2010 International Journal Of Air-Conditioning and Refr Vol.18 No.4

This review traces the development of nanofluid pool boiling from its beginning (1984) to the present through a sampling of studies that have interested the authors and which have led to the latest findings at the University of Texas at Arlington (UTA). The studies of thermophysical properties of nanofluids are briefly covered. Several works in the last 7 years are highlighted to illustrate the modes of nanofluid pool boiling testing, the variability of nanofluid boiling heat transfer (BHT), and the postulations of causes of this behavior. Starting in 2006, the wettability increase in the nanoparticle coating, generated during the nanofluid pool boiling, is recognized as the source of critical heat flux (CHF) enhancement through its effect on the dynamics of hot spots and departing bubbles. The reasons for the observed contradictory BHT behavior are not yet fully clear, but recently at UTA, nanofluid boiling heat transfer has shown to be transient due to the dynamic nature of the formation of the nanoparticle coating. Also at UTA, the mechanism of nanoparticle deposition on the heated surface has been further confirmed. Thus, nanofluid boiling has led back to heat transfer enhancement through surface modification in nanoscale. These developments from 2006 are covered in more detail.

A REVIEW OF ENHANCEMENT OF BOILING HEAT TRANSFER THROUGH NANOFLUIDS AND NANOPARTICLE COATINGS

SEUNG M. YOU,MIGUEL AMAYA,곽상묵 대한설비공학회 2010 International Journal Of Air-Conditioning and Refr Vol.18 No.4

This review traces the development of nanofluid pool boiling from its beginning (1984) to the present through a sampling of studies that have interested the authors and which have led to the latest findings at the University of Texas at Arlington (UTA). The studies of thermophysical properties of nanofluids are briefly covered. Several works in the last 7 years are highlighted to illustrate the modes of nanofluid pool boiling testing, the variability of nanofluid boiling heat transfer (BHT), and the postulations of causes of this behavior. Starting in 2006, the wettability increase in the nanoparticle coating, generated during the nanofluid pool boiling, is recognized as the source of critical heat flux (CHF) enhancement through its effect on the dynamics of hot spots and departing bubbles. The reasons for the observed contradictory BHT behavior are not yet fully clear, but recently at UTA, nanofluid boiling heat transfer has shown to be transient due to the dynamic nature of the formation of the nanoparticle coating. Also at UTA, the mechanism of nanoparticle deposition on the heated surface has been further confirmed. Thus, nanofluid boiling has led back to heat transfer enhancement through surface modification in nanoscale. These developments from 2006 are covered in more detail.

Effect of Subcooling on Pool Boiling of Water from Sintered Copper Microporous Coating at Different Orientations

Jun, Seongchul,Kim, Jinsub,You, Seung M.,Kim, Hwan Yeol Hindawi Limited 2018 Science and technology of nuclear installations Vol.2018 No.-

<P>The subcooling effect on pool boiling heat transfer using a copper microporous coating was experimentally studied in water for subcoolings of 10 K, 20 K, and 30 K at atmospheric pressure and compared to that of a plain copper surface. A high-temperature thermally conductive microporous coating (HTCMC) was made by sintering copper powder with an average particle size of 67 <I>μ</I>m onto a 1 cm × 1 cm plain copper surface with a coating thickness of ~300 <I>μ</I>m. The HTCMC surface showed a two times higher critical heat flux (CHF), ~2,000 kW/m<SUP>2</SUP>, and up to seven times higher nucleate boiling heat transfer (NBHT) coefficient, ~350 kW/m<SUP>2</SUP>K, when compared with a plain copper surface at saturation. The results of the subcooling effect on pool boiling showed that the NBHT of both the HTCMC and the plain copper surface did not change much with subcooling. On the other hand, the CHF increased linearly with the degree of subcooling for both the HTCMC and the plain copper surface. The increase in the CHF was measured to be ~60 kW/m<SUP>2</SUP> for every degree of subcooling for both the HTCMC and the plain surface, so that the difference of the CHF between the HTCMC and the plain copper surface was maintained at ~1,000 kW/m<SUP>2</SUP> throughout the tested subcooling range. The CHFs for the HTCMC and the plain copper surface at 30 K subcooling were 3,820 kW/m<SUP>2</SUP> and 2,820 kW/m<SUP>2</SUP>, respectively. The experimental results were compared with existing CHF correlations and appeared to match well with Zuber’s formula for the plain surface. The combined effect of subcooling and orientation of the HTCMC on pool boiling heat transfer was studied as well.</P>

Enhancement of pool boiling heat transfer in water on aluminum surface with high temperature conductive microporous coating

Godinez, Juan C.,Fadda, Dani,Lee, Jungho,You, Seung M. Elsevier 2019 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.132 No.-

<P><B>Abstract</B></P> <P>The effects of an aluminum high temperature conductive microporous coating (Al-HTCMC) on the nucleate boiling heat transfer (NBHT) coefficient and critical heat flux (CHF) are studied in saturated distilled water at 1 atm. Aluminum powders with three different mean particle diameters (d<SUB>m</SUB> = 11, 24, and 66 µm) are used in the fabrication of the Al-HTCMC. For each mean particle diameter, an optimal coating thickness to yield the highest NBHT coefficient is determined. The optimized Al-HTCMC thickness is found to result in comparable NBHT coefficients regardless of the particle diameter. Pool boiling tests with a plain aluminum surface are used for comparison. The coated and plain aluminum surfaces are treated equally before the pool boiling tests to establish a Boehmite oxidation nano layer on the aluminum surfaces. Following the Boehmite treatment, the contact angle is unmeasurable (∼0°) with the Al-HTCMC surface and 12° with a plain aluminum surface. Then, pool boiling tests are performed and reveal comparable CHF (1725–1850 kW/m<SUP>2</SUP>) values with or without the Al-HTCMC. However, the Al-HTCMC is shown experimentally to improve the NBHT coefficient by a factor of five as the wall superheat is reduced by from 31 K to 6 K just before CHF. The results obtained are also compared to similar work using an HTCMC layer on a copper surface to demonstrate the performance of the Al-HTCMC.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Study of the effects of an aluminum high temperature conductive microporous coating on pool boiling. </LI> <LI> Aluminum microporous coating (Al-HTCMC) fabricated using different aluminum powder particle sizes. </LI> <LI> Coating thickness optimized to yield highest nucleate boiling heat transfer coefficients. </LI> <LI> Boehmite treatment applied to aluminum surface with the microporous coating. </LI> </UL> </P>

스테노트로포모나스 말토필리아 각막염의 임상양상과 예후

유인천,이승현,박영걸,윤경철,In Cheon You,M,D,Seung Hyun Lee,M,D,Yeoung Geol Park,M,D,Ph,D,Kyung Chul Yoon,M,D,Ph,D 대한안과학회 2007 대한안과학회지 Vol.48 No.7

Purpose: To investigate the risk factor, clinical manifestations, treatment results, and prognoses in Stenotrophomonas maltophilia keratitis. Methods: Ten eyes of 10 patients who were diagnosed with, Stenotrophomonas maltophilia by corneal smear and culture were included in this study. Each patient`s past history, visual acuity, location and size of ulceration, hypopyon, treatment results and prognosis were analyzed retrospectively. Results: Seven pateints (70.0%) were men, and 3 were women. The mean age was 62.9±11.3 years. Only 2 eyes (20.0%) had previous histories of corneal traumas. Polymicrobial infections, including 3 cases infected with Pseudomonas species and 2 cases infected with Fusarium species, were detected in 7 eyes (70.0%). The lesions were located at the corneal center in 6 eyes, and hypopyon was observed in 9 eyes. The average size of ulceration was 28.5±19.6 mm2. Seven eyes (70.0%) underwent surgical treatment. The initial visual acuity was less than 0.02 in 9 eyes (90.0%). The final visual acuity improved in 3 eyes (30.0%) and was less than hand movement in 7 eyes (70.0%). Conclusions: Stenotrophomonas maltophilia keratitis occurs in patients with a compromised ocular surface, is often polymicrobial, and is associated with poor prognoses.

A Convergence Test of the Full-potential Linearized Augmented Plane Wave (FLAPW) Method : Ferromagnetic Bulk BCC Fe

Seung-Woo Seo,You Young Song,Gul Rahman,In Gee Kim,M. Weinert,A. J. Freeman 한국자기학회 2009 Journal of Magnetics Vol.14 No.4

The convergence behavior of the all-electron full-potential linearized augmented plane-wave (FLAPW) method with the explicit orthogonalization (XO) scheme is tested on ferromagnetic bulk body-centered-cubic Fe. Applying a commonly used criterion relating the plane-wave and angular momentum cutoffs, lmax = RMTKmax, where RMT is the muffin-tin (MT) sphere radius and Kmax is the plane-wave cutoff for the basis ? the total energy is converged and stable for KmaxRMT = 10. The total energy convergence dependence on the star-function cutoff, Gmax, is minimal and so a Gmax of 3Kmax or a large enough Gmax is a reasonable choice. We demonstrate that the convergence with respect to lmax or a fixed large enough Gmax and Kmax are independent, and that Kmax provides a better measure of the convergence than RMTKmax. The dependence of the total energy on RMT is shown to be small if the core states are treated equivalently, and that the XO scheme is able to treat systems with significantly smaller RMT than the standard LAPW method. For converged systems, the calculated lattice parameter, bulk modulus, and magnetic moments are in excellent agreement with the experimental values.

A Feasibility Study of Application of Laccase-based Time-Temperature Indicator to Kimchi Quality Control on Fermentation Process

Kang, You Jin,Kang, Jin-Won,Choi, Jung-Hwa,Park, Soo Yeon,Rahman, A.T.M. Mijanur,Jung, Seung Won,Lee, Seung Ju The Korean Society for Applied Biological Chemistr 2014 Applied Biological Chemistry (Appl Biol Chem) Vol.57 No.6

Kimchi, in factories or during transportation, is usually stacked on shelves at different heights, which affects temperature and thus kimchi quality. In this study, a time-temperature indicator (TTI) was used to control such quality variations. A case study was conducted to evaluate the validity of using the TTI; one group of small packages of young kimchi had the TTI attached whereas the other group did not. They were stored on shelves of different heights (i.e., top, middle, and bottom) in a laboratory fermentor. The samples with TTIs were individually fermented until the color of the TTIs reached a threshold level, whereas the samples without TTIs were collectively fermented for a predetermined time at a given temperature. The qualities of fermented samples including pH, acidity, microbial counts, and reducing sugars were analyzed. The samples with TTIs had more uniform qualities that were closer to the targets than those without TTIs. These results suggest that TTIs are practical tools to control kimchi quality in terms of temperature variation.

Ion-Exchangeable Functional Binders and Separator for High Temperature Performance of Li_1.1Mn_1.86Mg_0.04O₄ Spinel Electrodes in Lithium Ion Batteries

Woo, Seung Hee,Lim, Hyung-Woo,Jeon, Sangbin,Travis, Jonathan J.,George, Steven M.,Lee, Se-Hee,Jo, Yong Nam,Song, Jun Ho,Jung, Yoon Seok,Hong, Sung You,Choi, Nam-Soon,Lee, Kyu Tae The Electrochemical Society 2013 Journal of the Electrochemical Society Vol.160 No.11

<P>Since LiMn<SUB>2</SUB>O<SUB>4</SUB> spinel materials are inexpensive, environmentally-friendly, and safe, they are considered a promising cathode candidate for lithium ion batteries in EVs to replace commercialized materials such as LiCoO<SUB>2</SUB>, LiNi<SUB>1/3</SUB>Mn<SUB>1/3</SUB>Co<SUB>1/3</SUB>O<SUB>2</SUB> and LiNi<SUB>0.5</SUB>Co<SUB>0.2</SUB>Mn<SUB>0.3</SUB>O<SUB>2</SUB>. However, LiMn<SUB>2</SUB>O<SUB>4</SUB> spinel electrodes severely degrade at high temperature due to Mn dissolution. Also, the dissolved Mn<SUP>2+</SUP> ions causes self-discharge where reduction of Mn<SUP>2+</SUP> ions into Mn metals occurs on a graphite anode surface accompanied by oxidation of lithiated graphite at a charged state, and this results in severe capacity fading at high temperature. In this study, ion-exchangeable binders and a separator having functional groups of sodium carboxylate or sulfonate are, for the first time, examined to solve the Mn dissolution problem of LiMn<SUB>2</SUB>O<SUB>4</SUB> spinel materials at high temperature. Ion exchange between Na<SUP>+</SUP> ions of the functional groups of the binders and the separator and dissolved Mn<SUP>2+</SUP> ions of the LiMn<SUB>2</SUB>O<SUB>4</SUB> electrodes inhibits self-discharge, resulting in improved cycle performance. This result is supported by the IR spectra of the binders, an ICP analysis of the electrolytes, and ex situ XRD patterns of lithiated graphite electrodes.</P>

EFFECT OF SOLUBLE ADDITIVES, BORIC ACID (H₃BO₃) AND SALT (NaCl), IN POOL BOILING HEAT TRANSFER

Kwark, Sang-M.,Amaya, Miguel,Moon, Hye-Jin,You, Seung-M. Korean Nuclear Society 2011 Nuclear Engineering and Technology Vol.43 No.3

The effects on pool boiling heat transfer of aqueous solutions of boric acid ($H_3BO_3$) and sodium chloride (NaCl) as working fluids have been studied. Borated and NaCl water were prepared by dissolving 0.5~5% volume concentration of boric acid and NaCl in distilled-deionized water. The pool boiling tests were conducted using $1{\times}1\;cm^2$ flat heaters at 1 atm. The critical heat flux (CHF) dramatically increased compared to boiling pure water. At the end of boiling tests it was observed that particles of boric acid and NaCl had deposited and formed a coating on the heater surface. The CHF enhancement and surface modification during boiling tests were very similar to those obtained from boiling with nanofluids. Additional experiments were carried out to investigate the reliability of the additives deposition in pure water. The boric acid and NaCl coatings disappeared after repeated boiling tests on the same surface due to the soluble nature of the coatings, thus CHF enhancement no longer existed. These results demonstrate that not only insoluble nanoparticles but also soluble salts can be deposited during boiling process and the deposited layer is solely responsible for significant CHF enhancement.