소수성 표면 마이크로 채널 내에서의 삼중선에 의한 압력강하의 실험적 연구

Abstract

Slug flow regime is more broaden than the others in microchannels comparing with flow of conventional channels. Moreover, flow pattern is different according to wettability of surface in microchannels. Generally, bubbles in the slug flow regime are lubricated by liquid film in hydrophilic microchannels. However, bubbles are not lubricated by liquid film in hydrophobic microchannels. So, triple-lines are generated at the interface of the bubble. And the non-lubricated bubbles made higher pressure drop than the lubricated bubbles due to the moving of the triple-line. In previous researches, the pressure drop of triple-line is affected by following parameters.

channel diameter, dynamic contact angle, fluid property. And, dynamic contact angle is affected by following parameters.

static contact angle, superficial velocity, fluid property. Namely, channel diameter, static contact angle, superficial velocity, fluid property have influence on the pressure drop of the triple-line in micorchannels.To understand effect of the parameters, experiments were conducted with various channel diameters(2.076, 1.555, 1.018, 0.763, 0.546 mm), superficial velocity(0.01～0.4 m/s), fluids(water, 1, 5, 10% ethanol-water). Increasing superficial velocity, and decreasing channel diameter, and ethanol mole fraction, the pressure drop of triple-lines was increased. Comparing with previous researches(Jiang et al., Bracke et al, Seebergh et al.), the pressure drop of triple-line in this study was overestimated. In order to understand this cause, dynamic contact angle was compared between this study and previous researches, because it is the dominant dependent parameter of the pressure drop of triple-lines. In previous researches, dynamic contact angle is correlated with universal relations. Universal relation is consisted of static contact angle and capillary number. Universal relation has constraints according to dominant forces acting on interface shape. For example, the universal relation of Jiang et al. is available when dominant forces are only interfacial and viscous force. Also, the universal relation of Bracke et al. and Seebergh et al. is available when dominant force are interfacial, viscous, and gravitational force. However, in this study, dominant forces acting on interface shape were interfacial, viscous, and inertial force. Owing to different dominant forces, dynamic contact angle predicted by previous researches was underestimated. therefore pressure drop of triple-lines was underestimated comparing this study's.So, in this experimental region (0.0001≤Ca≤0.001, 0.01≤We≤0.1, 68°≤θS≤110°), the corrected universal relations was proposed. New proposed correlation predicted dynamic contact angle in 5% error. In addition, pressure drop of triple-lines based on the proposed correlation was predicted in 26% error.