* 2016.11.14 受付 ** 慶應義塾大学大学院理工学研究科開放環境科学専攻 〒223-8522 神奈川県横浜市港北区日吉 3-14-1 TEL: (045)566-1575 FAX: (045)566-1575 E-mail: [email protected]*** 慶應義塾大学理工学部応用化学科 特集号論文推薦原稿 水平摺動するノズルからの微細気泡生成 * Smaller Bubble Formation from a Horizontally Oscillating Nozzle 村 上 大地郎 ** 寺 坂 宏 一 *** 藤 岡 沙都子 *** MURAKAMI Daijiro TERASAKA Koichi FUJIOKA Satoko Abstract Fine bubbles are used for cleaning system, separating process, food industry and so on. However, commercially available devices for fine bubble generation cannot be applied for particle dispersion liquid because they need liquid pumps and particles are accumulated on their systems. Moreover, the bubble diameter cannot be controlled in those devices. The uniformed and controlled bubble diameter is important for a reasonable industrial device design. Therefore, in this study, a novel method for fine bubble generation without liquid circulation was developed. A horizontally oscillating micro-nozzle was used to make bubbles small. The effect of the gas flow rate, the oscillating frequency, and the oscillation amplitude on the average bubble diameter was investigated experimentally. Moreover, visualization and quantification of liquid motion around the oscillating nozzle was carried out in this study. It was clarified that the liquid viscous force due to the relative velocity of the nozzle motion to the liquid motion enhances the bubble detachment from the nozzle in this method. Keywords: Fine bubble, Oscillating Micro-nozzle, Bubble formation, Bubble dispersion 1. 緒 言 気液接触装置はガス吸収器、気泡塔、バイオリ アクターなど多くの工業装置に利用されており、 気液接触面積はプロセス性能に大きく影響する。 気液間の物質移動の向上には気泡の微細化や合 体防止、工業装置設計には気泡直径の均一化や制 御が重要である。既存の発生装置では外部液循環 ラインなど複雑な構造や、気泡径が自由に制御で きないなどの欠点がある[1-3]。そこで、外部への 液の取り出しが不要かつ生成気泡径の制御が可 能な気泡の微細化技術の開発が期待されている。 気泡径を制御可能な気泡発生法として、単一孔 において成長過程の気泡に対して、気泡成長方向 に垂直な水流(十字流)を加えて気泡のせん断を 行い、単一孔からの早期離脱を促す方法が挙げら れる[4]。Tan et al. (2000) は十字流条件下におけ る非球形気泡成長モデルを提案し、実験結果と計 算結果の良好な一致を得た [5] 。 Tokanai et al. (2000) は、十字流条件において気泡の微細化の様 子を観察し、十字流中条件で生成する気泡の容積 を、静止液中で単一孔から離脱するの際のフォー スバランスに粘性力および気泡形状を考慮に入 れたモデルで表現した[6]。 Terasaka et al. (2003) は 二重円管を用いて発生させた螺旋液流を用いて、 高粘性液体中でノズルから生成する気泡の微細 化およびサイズ制御に成功し、ガス流量およびせ ん断速度から気泡容積が決定する相関式を導出 した[7]。 さらに、液の運動ではなく、ノズル自身の振動 により気泡離脱を促進する方法が検討されてい Japanese J. Multiphase Flow Vol. 31 No. 4(2017) 422
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Smaller Bubble Formation from a Horizontally Oscillating Nozzle
村 上 大地郎 ** 寺 坂 宏 一
*** 藤 岡 沙都子 ***
MURAKAMI Daijiro TERASAKA Koichi FUJIOKA Satoko
Abstract Fine bubbles are used for cleaning system, separating process, food industry and so on. However, commercially available devices for fine bubble generation cannot be applied for particle dispersion liquid because they need liquid pumps and particles are accumulated on their systems. Moreover, the bubble diameter cannot be controlled in those devices. The uniformed and controlled bubble diameter is important for a reasonable industrial device design. Therefore, in this study, a novel method for fine bubble generation without liquid circulation was developed. A horizontally oscillating micro-nozzle was used to make bubbles small. The effect of the gas flow rate, the oscillating frequency, and the oscillation amplitude on the average bubble diameter was investigated experimentally. Moreover, visualization and quantification of liquid motion around the oscillating nozzle was carried out in this study. It was clarified that the liquid viscous force due to the relative velocity of the nozzle motion to the liquid motion enhances the bubble detachment from the nozzle in this method. Keywords: Fine bubble, Oscillating Micro-nozzle, Bubble formation, Bubble dispersion
1. 緒 言
気液接触装置はガス吸収器、気泡塔、バイオリ
アクターなど多くの工業装置に利用されており、
気液接触面積はプロセス性能に大きく影響する。
気液間の物質移動の向上には気泡の微細化や合
体防止、工業装置設計には気泡直径の均一化や制
御が重要である。既存の発生装置では外部液循環
ラインなど複雑な構造や、気泡径が自由に制御で
きないなどの欠点がある[1-3]。そこで、外部への
液の取り出しが不要かつ生成気泡径の制御が可
能な気泡の微細化技術の開発が期待されている。
気泡径を制御可能な気泡発生法として、単一孔
において成長過程の気泡に対して、気泡成長方向
に垂直な水流(十字流)を加えて気泡のせん断を
行い、単一孔からの早期離脱を促す方法が挙げら
れる[4]。Tan et al. (2000) は十字流条件下におけ
る非球形気泡成長モデルを提案し、実験結果と計
算結果の良好な一致を得た [5]。Tokanai et al.
(2000) は、十字流条件において気泡の微細化の様
子を観察し、十字流中条件で生成する気泡の容積
を、静止液中で単一孔から離脱するの際のフォー
スバランスに粘性力および気泡形状を考慮に入
れたモデルで表現した[6]。Terasaka et al. (2003) は
二重円管を用いて発生させた螺旋液流を用いて、
高粘性液体中でノズルから生成する気泡の微細
化およびサイズ制御に成功し、ガス流量およびせ
ん断速度から気泡容積が決定する相関式を導出
した[7]。
さらに、液の運動ではなく、ノズル自身の振動
により気泡離脱を促進する方法が検討されてい
Japanese J. Multiphase Flow Vol. 31 No. 4(2017)422