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EXPERIMENTAL POOL BOILING HEAT TRANSFER STUDY OF THE NANOPOROUS COATING IN VARIOUS FLUIDS
곽상묵,MIGUEL AMAYA,SEUNG M. YOU 대한설비공학회 2012 International Journal Of Air-Conditioning and Refr Vol.20 No.1
An experimental pool boiling study was conducted using plain and nanoporous coated heater surfaces immersed in various working fluids: water, ethanol and HFE-7100. Pool boiling tests were performed on flat 1 cm × 1 cm heaters. Unlike in water, the critical heat flux (CHF) enhancement of the nanoporous coating seems to be less or marginal in ethanol and HFE-7100 at 1 atm. The reduced effect of the nanoporous coating in ethanol and HFE-7100 is believed to be due to the highly wetting nature of these fluids since no obvious difference in wettability is observed between nanoporous coated and uncoated surfaces through apparent contact angle measurement. Moreover, pressure effects were also investigated for the fluids mentioned above. For the nanoporous coated surface, CHF enhancement of the nanoporous coating appeared to be dependent on the test pressure, showing greater CHF enhancement at lower pressure. It is believed that this pressure dependent CHF enhancement behavior could be closely related to the bubble departure diameter. As pressure lowers, the departure bubble size increases and this allows the nanoporous coating to become more influential, even for the highly wetting fluids, in delaying local dry-out, which in turn results in increasing CHF enhancement.
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EFFECT OF SOLUBLE ADDITIVES, BORIC ACID (H_3BO_3) AND SALT (NaCl), IN POOL BOILING HEAT TRANSFER
곽상묵,MIGUEL AMAYA,HYEJIN MOON,SEUNG M. YOU 한국원자력학회 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 x 1 cm2 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.
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해수 환경에서의 철근과 GFRP리바의 굽힘강도 특성에 관한 연구
한길영,최명선,곽상묵 朝鮮大學校 機械技術硏究所 2003 機械技術硏究 Vol.6 No.1
Fiber reinforced plastics(FRP) attracted muGh attention as a form of concrete reinforcement in the past decade. Compared with existing construction matrials, FRP possesses many advantages such as light-weight. high-strength, corrosion resistant properties, etc. Among other fabrication process of GFRP, pultrusion is one of the promising ones for civil infrastructure application. This paper describes the need for a ductile Fiber Reinforced Plastics (FRP) reinforcement for concrete structures. To promte the degradation of the adhesive condition a t the fiber-matrix micro interface without matrix dissolution loss were carried out in salt water surrounding. The absorption properties and the bending strength were compared about GFRP rebar and steel bar. Due to the fiber permeability absorption of moisture take place through both the fiber and the matrix. The diffusivities obtained for Glass-Polyester are found to be in good agreement with those available in the existing literature.
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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.
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