The effect of initial flow velocity on the liquid film thickness in micro tube accelerated slug flow

Abstract

Liquid film thickness is an important parameter for predicting boiling and condensation heat transfer in micro tubes. In the present study, the effect of initial flow velocity on the liquid film thickness in accelerated flows under adiabatic condition is experimentally investigated. The laser focus displacement meter is used to measure the initial liquid film thickness. Circular tube with inner diameter of 1 mm was used for the test tube, and water, ethanol and FC-40 are used as working fluids. When the flow is accelerated from small initial velocities under small Bond number condition, initial liquid film thickness is identical to that of steady flow at small capillary numbers, and then deviates from the steady condition and eventually follows that of accelerated flow from zero initial velocity as capillary number is increased. When the flow is accelerated from large initial velocities, initial liquid film thickness deviates from the steady condition earlier and starts to follow that of accelerated flow from zero initial velocity

The effect of bubble deceleration on the liquid film thickness in microtubes

“…The tube is horizontally oriented, and the instantaneous bubble velocities and liquid film thicknesses are measured from the side of the tube. LFDM has been already used by several researchers to measure liquid film thickness (Takamasa & Kobayashi, 2000;Hazuku et al, 2005;Han & Shikazono, 2009a, 2009bYoun et al, 2015). Figure 2 shows the principle of the LFDM.…”

“…The thickness just after the initial rapid decrease is defined as the initial liquid film thickness δ 0 as shown in Fig. 7 (Han & Shikazono, 2009a, 2009bYoun et al, 2015). respectively.…”

“…The scattering length (δ 2 -δ 1 ) is less than 2% of the liquid film thickness in the present study. Refer to (Han & Shikazono, 2009a;Youn et al, 2015) for the details.…”

Study on liquid film formed with liquid column oscillation in pulsating heat pipe (Measurement of liquid film thickness using forced oscillation system)

“…No.19-00307 [DOI: 10.1299/transjsme.19-00307] *1 正員，神奈川大学 工学部(〒221-8686 神奈川県横浜市神奈川区六角橋 3-27-1) *2 神奈川大学 工学部 E-mail of corresponding author: mmiura@kanagawa-u.ac.jp にすることは重要である．そのなかで，液膜の厚さは，細管流路内における相変化熱伝達を予測するための重要 なパラメーターである (Thome et al, 2004． 流路内を移動する液柱が形成する液膜の厚さに関してはこれまで多くの研究が行われている．Fairbrother らは， 円管流路内を移動する気泡に関して実験研究を行い， 気泡移動に伴い形成される液膜の厚さを推算するとともに， 粘性力と毛管力の比であるキャピラリー数を用いて液膜厚さを整理し，その実験結果に基づいて液膜厚さの予測 式を提案した (Fairbrother and Stubbs, 1935)．しかし，この提案された予測式の物理的意味については明らかにさ れなかった．Landau らは，平板を液槽から引き上げたときに平板表面上に生じる液膜の厚さを評価した (Landau and Levich, 1942) (Bretherton, 1961)．また，Aussillous らも，円管流路内壁 に形成される液膜厚さの理論解を求め，Taylor の行った実験データ (Taylor, 1961) に対してフィッティングする ことで半経験的な予測式を提案した (Aussillous and Quéré, 2000)．さらに，Taylor の実験と比較して低い粘性係数 の作動液体を使用するとともに，高速で液柱を移動させることにより，慣性力や速度境界層が液膜厚さに及ぼす 影響を明らかにした (Aussillous and Quéré, 2000)．近年では，Han ら，Youn らが種々の液柱流動条件において流路 内に形成される液膜の厚さをレーザーフォーカス変位計により測定し，キャピラリー数・Weber 数・Reynolds 数・ Bond 数の無次元数を用いた液膜厚さの予測式を提案している (Han and Shikazono, 2009a, 2009b, 2010, Youn et al, 2015．具体的には，液柱が一定速度で移動する場合 Shikazono, 2009a, 2009b)，液柱が一定加速度…”

Heat transfer and flow characteristics of thermally induced two-phase oscillating flow in micro tubes

“…Youn et al (2015) conducted experiments to investigate the effect of acceleration on liquid film thickness in circular tubes. Han et al (2015) measured liquid film thickness in annular flows in micro tubes.…”