• Journal of Advanced Marine Engineering and Technology
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• 제38권5호
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• pp.581-588
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• 2014

Extensive researches toward pool boiling characteristics have been widely investigated. However, the correct understanding of its boiling crisis by Critical Heat Flux (CHF) phenomenon during steady and transient heat transfer as a fundamental database for designing heat generation systems is still need to be clarified. The pool boiling CHFs were investigated to clarify the generalized phenomena of transition to film boiling at transient condition. The CHFs were measured on 1.0 mm diameter horizontal cylinder of platinum for exponential heat generation rates with various periods for saturated liquids at atmospheric pressure. The incipience of boiling processes was completely different depending on pre-pressurization. Also, the dependence of pre-pressure in transient CHFs changed due to the wettability of boiling liquids. The trend of typical CHFs were clearly divided into the first, second and third groups for long, short and intermediate periods, respectively. By the effect of pre-pressurization, the boiling incipience mechanism was replaced from that by active cavities entraining vapor to that by the HSN in originally flooded cavies.

• Nuclear Engineering and Technology
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• 제43권3호
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• pp.195-204
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• 2011

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.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.373-378
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• 2000

An experimental investigation on the incipience of nucleate boiling in forced flow of water is performed as a verification and extension of previous analysis. The effects of the subcooling, Reynolds number and surface curvature on the onset of nucleate boiling(ONB) in a concentric annulus flow channel with smooth inner heating surface is investigated experimentaly. Through flow visualization, the boiling phenomenon was observed directly and the experimental results were examined to find ONB heat flux. The results show that the variation of heat flux at ONB is increased linearly as the Reynolds number and subcooling are increased. The effect of surface curvature is very great specially for a small radius when radius of the inner heating tube is increased, the heat flux at ONB is almost inversely increased for the range of this investigation. It is found that the effect of convex surface curvature on ONB heat flux is very significant for a small radius.

• 한국잠사곤충학회지
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• 제29권1호
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• pp.31-38
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• 1987

누에 이면교잡에 의해 F1세대의 견층 연감율, sericin량 및 fibroin량을 유전 분석한 결과는 다음과 같다. 1. Vr-Wr graph에서 자웅간의 견층 연감율은 모두 초우성이고, 자웅간의 sericin량과 fibroin량은 모두 불완전 우성이었다. 2. 각 형질에 대한 분산성분의 추정에서 자웅간의 sericin 량과 fibroin량 및 자의 연감율에서는 유전자의 상가적효과가 우성효과보다 큰 경향이었고, 웅의 연감율에서만 반응이 양상이었다. 3. 우성의 방향에 있어서는 자웅간의 sericin량과 fibroin량에서 모두 높은 방향으로, 자웅간의 연감율에서는 낮은 쪽이 우성이었다. 4. 조합능력은 3개 형질의 자웅 모두 유의적으로 작용하였고, 특정조합능력보다 일반조합능력이 크게 평가되었다.

• 설비공학논문집
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• 제17권8호
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• pp.714-721
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• 2005

The water jet impingement cooling with boiling is one of the techniques to remove heat from high heat flux equipments. The configuration of surface roughness is one obvious condition of affecting the performance on heat transfer in nucleate boiling, The present study investigates the water jet impinging single-phase convection and nucleate boiling heat transfer for the effect of surface roughness to enhance the heat transfer in free surface and submerged jet. The distributions of the averaged wall temperature as well as the boiling curves are discussed. Jet velocities are varied from 0.65 to 1.7 m/s. Surface roughness by sand blast and sand paper varies from 0.3 to 2.51 ${\mu}m$ and cavity shapes on surface are semi-circle and v-shape, respectively The results showed that higher velocity of the jet caused the boiling incipience to be delayed more. The incipient boiling and heat transfer increase with increasing surface roughness due to a large number of cavities of uniform size.

• 설비공학논문집
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• 제3권5호
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• pp.395-403
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• 1991

The purpose of this investigation was to characterize nucleate boiling and burn-out heat flux for rectangular free jet with saturated water impinging perpendicularly and upward against a flat uniform heat flux surface. Heat flux measured for Reynolds number based on rectangular nozzle width and for aspect ratio. The result of nucleate boiling heat transfer was presented nondimensional experimental equation including Nusselt, Boiling, Subcooling, Reynolds and Weber number. The effect of aspect ratio of heated surface in the burn-out heat flux had not appeared distinctly. But for the same aspect ratio, burn-out heat flux increased linearly with increment of nozzle exit velocity.

• 설비공학논문집
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• 제13권6호
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• pp.440-447
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• 2001

This study investigate experimentally the effect of in height, thickness, and clearance on the boiling heat transfer. The heat surfaces having copper fin array is tested for pool boiling. The gas-liquid exchange interference is investigated based on fin array clearance. These test results can be applied to the design of tube bundle system. The fin height of 2 mm is found to be effective. Effects of heat transfer promotion reaches the highest level when the fin clearance is 0.5mm. Also, heat flux is increased when the fin thickness is smaller. But0.2 mm fin thickness is highly recommended.

• 한국자동차공학회논문집
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• 제14권5호
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• pp.9-16
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• 2006

The present study is to simulate coolant flow in IC engine cooling passages under subcooled nucleate boiling conditions and investigate thermal stress analysis of the solid part. To consider nucleate boiling heat transfer effect, Chen's empirical formula is used through user subroutine programing in CFD code and then nucleate boiling model is compared with Robinson's experimental results, which shows reasonable agreement. This Chen's nucleate boiling model is applied to single cylinder IC engine model and we do cylinder liner thermal stress analysis using commercial FEM code.

• 에너지공학
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• 제15권1호
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• pp.35-44
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• 2006

본 연구에서는 비등열전달 과정동안, 초음파 진동이 열전달 과정에 미치는 영향에 관하여 실험적으로 조사해 보았다. 실험은 등온가열조건하에서, 40kHz의 초음파 진동을 가진한 경우와 가진하지 않은 경우로 나누어 비등과정동안의 온도분포를 측정하였고, 대류상태와 과냉상태 그리고 포화상태에서의 열전달계수를 측정하여 열전달 향상율을 비교하여 보았다. 또한, 하이드로폰을 이용하여 초음파 가진시 매질내에 발생하는 음압분포를 측정하고 열전달 향상율과 비교하여 보았다. 실험결과, 비등열전달 과정에 초음파 진동을 가진한 경우, 가진하지 않은 경우와 비교하였을 때 열전달계수가 높게 나타나는 것을 확인하였으며, 특히 대류상태에서 열전달계수가 급격하게 증가하였다. 또한, 초음파 진동의 가진으로 인해 형성되는 음압은 진동자가 부착된 지점에서 주위보다 상대적으로 높게 형성되는 것을 실험적으로 확인하였으며, 초음파 진동으로 인해 형성된 높은 음압이 열전달 향상율에 영향을 미치는 원인의 하나로 작용하고 있음을 알 수 있었다. 결국, 초음파 진동에 의해 매질내에 발생하는 음압은 열전달 향상과 밀접한 관련이 있다고 사료된다.

• 한국추진공학회지
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• 제18권2호
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• pp.42-51
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• 2014

기존 항공유보다 비등점을 높인 고비등점 연료에 대하여 다양한 분사 압력 조건에서 비등점 이상의 온도까지 연료를 가열하는 경우의 분사특성을 실험적으로 연구하였다. 연료 온도 상승에 따른 인젝터의 특성은 유량계수(${\alpha}$)와 캐비테이션 수($K_c$)를 파라미터로 나타내었는데, 고온에서의 각 연료별 ${\alpha}$ 특성을 $K_c$에 대해 나타내면 그 경향이 모두 유사한 것으로 확인되었다. 한편, 고비점 연료들은 기존 연료에 비하여 비등의 효과가 나타나기 시작하는 온도가 더 높아졌을 뿐만 아니라, 그 이상의 온도에서도 분사 특성에 미치는 인젝터 내부의 비등 영향을 더 적게 받았다.