Bubble dynamics at boiling incipience in subcooled upward flow boiling

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

“…2. In this case, only one nucleation site was activated within the visualization section, and all the bubbles produced at this site were lifted off the vertical heated surface immediately after the nucleation to disappear quickly in the subcooled bulk liquid as reported in our previous paper [14]. In consequence, no bubbles hit the probe tip although a number of bubbles were produced.…”

“…Experimental apparatus and procedure are described only briefly since they were similar to those used in our previous work [14]. Configuration of the experimental loop is depicted in Fig.…”

“…Therefore, although these correlations are useful to estimate the PNVG, it would not necessarily be guaranteed that the bubble departure or the bubble lift-off is the key phenomenon to cause NVG. In fact, several investigators visualized the bubble behavior in water subcooled flow boiling to observe that the bubbles did not stay at the nucleation sites even under the conditions close to ONB [10][11][12][13][14]. For instance, in the experiments conducted by the present authors [14], the bubble behavior at ONB was significantly dependent on the pressure; the bubbles were lifted off the heater surface immediately after the nucleation near the atmospheric pressure whilst they slid along the vertical heated surface for a long distance at elevated pressures.…”

Onset of Nucleate Boiling in Mini and Microchannels: A Brief Review

“…For instance, Basu et al (2002) indicated that single-phase heat transfer prevails upstream of the ONB point, but the presence of bubbles permits various heat transfer mechanisms downstream of it. It is also reported that the bubble behavior at ONB can significantly be different depending on the experimental setup (Bibeau and Salcudean, 1994;Thorncroft et al, 1998;Okawa et al, 2005;Ahmadi et al, 2012). In consequence, many correlations and models have been developed so far to predict the location of ONB in subcooled flow boiling; some of them are discussed in the following section.…”

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

“…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…”