Experimental identification of the phenomenon triggering the net vapor generation in upward subcooled flow boiling of water at low pressure

Ahmadi, Rouhollah; Ueno, Takayoshi; Okawa, Tomio

doi:10.1016/j.ijheatmasstransfer.2012.06.020

Cited by 19 publications

(3 citation statements)

References 13 publications

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“…This is because of three reasons: a) during the i n t e r n a t i o n a l j o u r n a l o f r e f r i g e r a t i o n 5 6 ( 2 0 1 5 ) 3 7 e4 2 vacuum cooling process, degree of superheat is fundamentally caused by the pressure drop; b) the increasing of bubble size depends largely on the pressure drop from the tube bottom to water surface during immersion vacuum cooling; c) the bubbles at the tube bottom are more difficult to grow up than the upper ones, which is different from the phenomenon in cooking process (Ahmadi et al, 2012). Consequently, controlling the pressure drop rate seems to be one of the fundamental methods to improve the effect of vacuum cooling.…”

Section: Resultsmentioning

confidence: 99%

Mechanism of spillage and excessive boiling of water during vacuum cooling

Song

Liu

Jaganathan

et al. 2015

International Journal of Refrigeration

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Section: Resultsmentioning

confidence: 99%

Mechanism of spillage and excessive boiling of water during vacuum cooling

Song

Liu

Jaganathan

et al. 2015

International Journal of Refrigeration

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“…They also observed bubbles merging on the nucleation site due to increases on heat flux. Ahmadi et al (2012) observed that at high liquid subcooling close to the onset of nucleate boiling conditions, all nucleated bubbles departed for the heater wall and condensed. For lower subcooling levels, bubbles reattached to the wall after lift-off, consequently the bubble lifetime was increased.…”

Section: Introductionmentioning

confidence: 99%

Multi-scale full-field measurements and near-wall modeling of turbulent subcooled boiling flow using innovative experimental techniques

Hassan

2016

Nuclear Engineering and Design

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Multi-phase flows are one of the challenges on which the CFD simulation community has been working extensively with a relatively low success. The phenomena associated behind the momentum and heat transfer mechanisms associated to multi-phase flows are highly complex requiring resolving simultaneously for multiple scales on time and space. Part of the reasons behind the low predictive capability of CFD when studying multi-phase flows, is the scarcity of CFD-grade experimental data for validation. The complexity of the phenomena and its sensitivity to small sources of perturbations makes its measurements a difficult task. Non-intrusive and innovative measuring techniques are required to accurately measure multi-phase flow parameters while at the same time satisfying the high resolution required to validate CFD simulations. In this context, this work explores the feasible implementation of innovative measuring techniques that can provide whole-field and multi-scale measurements of two-phase flow turbulence, heat transfer, and boiling parameters. To this end, three visualization techniques are simultaneously implemented to study subcooled boiling flow through a vertical rectangular channel with a single heated wall. These techniques are listed next and are used as follow: 1) High-speed infrared thermometry (IR-T) is used to study the impact of the boiling level on the heat transfer coefficients at the heated wall, 2) Particle Tracking Velocimetry (PTV) is used to analyze the influence that boiling parameters have on the liquid phase turbulence statistics, 3) Highspeed shadowgraphy with LED illumination is used to obtain the gas phase dynamics. To account for the accuracy and to complement these innovative techniques, redundant and simultaneous measurements are performed by means of thermocouples, flow and power meters, differential and absolute pressure transducers, etc. The present experiments are intended to improve the understanding of subcooled boiling flow and to provide reliable and accurate subcooled boiling flow experimental information for verification and validation of two-phase flow computational models.

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“…緒言強制対流サブクール沸騰では、強制対流熱伝達と核沸騰熱伝達が共存するため、高い伝熱性能が得られる [1]。このため、高発熱密度電子機器や核融合炉第一壁など、高熱流束除熱が要求される機器の冷却への応用が検討されている [2,3]。また、沸騰水型軽水炉(BWR)では、炉心内のサブクール沸騰域におけるボイド率が、燃料の燃焼度、圧力損失、二相流動安定性に影響を及ぼす [4,5]。このため、強制対流サブクール沸騰における伝熱及びボイド率発展のメカニズムを解明することは、工業的に重要な課題である。一方、サブクール沸騰域における気泡挙動を観察対象として、これまで数多くの可視化実験が行われている。この結果、発泡核上における気泡の成長と凝縮 [6]、鉛直伝熱面に沿う気泡のスライド上昇 [7,8]、鉛直伝熱面からの気泡離脱 [8][9][10] *+ $ù RST%&26 \b *+ 7Ö î ×H288 789 7Ö î *+ 9:7 8C& ,;<=>2 8 9 a c? 0*+ 9:78C& @642789…”

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Bubble Lift-off from a Vertical Heated Surface in Subcooled Pool Boiling

Miyano¹,

Okawa²

2016

JAPANESE JOURNAL OF MULTIPHASE FLOW

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Experiments were carried out to explore the mechanisms of bubble lift-off from a vertical heated surface in subcooled pool boiling. The experiments were conducted at atmospheric pressure and distilled water was used as the test fluid. A high speed camera was used for observation of bubble behavior. The main experimental parameters were the static contact angle of the heated surface, the liquid subcooling, and the wall heat flux. The time variation of bubble size was measured through image analysis. The growth force acting on the bubble was calculated using the measured time-evolution of the bubble size. The bubble growing on the vertical heated surface started to be extended in the horizontal direction when the sign of the growth force turned from negative to positive. It was hence considered that the growth force is one of the main causes of the bubble lift-off from a vertical heated surface. Furthermore, a correlation was developed for the bubble lift-off diameter considering the distribution of heat transfer rate around the bubble.

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Experimental identification of the phenomenon triggering the net vapor generation in upward subcooled flow boiling of water at low pressure

Cited by 19 publications

References 13 publications

Mechanism of spillage and excessive boiling of water during vacuum cooling

Mechanism of spillage and excessive boiling of water during vacuum cooling

Multi-scale full-field measurements and near-wall modeling of turbulent subcooled boiling flow using innovative experimental techniques

Bubble Lift-off from a Vertical Heated Surface in Subcooled Pool Boiling

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