Session: 11-01: Micro/Miniature Two-Phase Devices/ Systems

Paper Number: 130963

130963 - An Experimental Investigation on Characteristics of Liquid Film Thickness of Gas-Liquid Taylor Flow in Rectangular Microchannel 

Abstract: 

Microchannel heat exchangers have been widely studied and applied because of the compact structure and superior heat transfer capacity. Liquid film thickness plays a key role in the calculation of pressure drop, heat transfer coefficient and void fraction of gas-liquid two-phase flow. The formation mechanism of gas-liquid Taylor flow in rectangular microchannels is complex, and the dynamic characteristics of liquid film are still unclear. Due to the limitation of precision measurement technology, the measurement data of liquid film thickness in rectangular microchannels are very limited. Most measured liquid film thickness are concentrated on the gas-liquid two-phase flow in circular tubes. In 1961, Bretherton deduced from Reynolds's lubrication theory that the dimensionless initial liquid film thickness of circular microchannels was proportional to Ca raised to the power of two-thirds^[1]. In 2000, Aussillous and Quere improved Bretherton's theoretical model and proposed the famous Taylor theorem^[2]. They divided a capillary force dominant region and an inertia force dominant region that affected the formation of liquid film. In 2009, Han and Shikazono^[3] obtained the quantitative relationship between the initial liquid film thickness in a micro circular tube and Ca, Re and We. They found out that the liquid film thickness in a micro circular tube was not only affected by the capillary number, but also closely related to Reynolds number and Weber number. Compared with uniform distribution of liquid film in a circular tube, the circumferential distribution of liquid film in rectangular microchannels is uneven due to the corner of the cross section. The difference in liquid film thickness between the central and the corner can easily lead to the rupture of the central liquid film, resulting in the change of flow pattern and even the change of heat and mass transfer mechanism. Hence, it is necessary to carry out precise measurement and analysis of liquid film thickness of gas-liquid two-phase flow in rectangular microchannels. The work is expected to be helpful to explore the dynamics of liquid film in rectangular microchannels, and reveal the heat and mass transfer characteristics in microchannel flow boiling and condensing.

Surface tension and viscous force are both important factors affecting liquid film thickness. In the present work, the effects of surface tension and hydraulic diameter on the characteristics of liquid film in rectangular microchannels were investigated by using Laser confocal displacement method and visualization experiments. Figure 1 showed the picture of experimental setup in the present experiment. As shown in Figure 1, the laser confocal displacement meter (KEYENCE LT-9011) was used to measure the liquid film thickness, the high-speed data acquisition instrument (KEYENCE NR-500, NR-HA08) recorded the displacement data, and the high-speed camera (PHOTRON FASTCAM Mini AX) was used for synchronous image acquisition. Injection pumps were used for air and water supply. In order to adjust the surface tension of fluid, Tween-20 was used to reduce the surface tension coefficient of water, and the solution concentrations were 0.1, 0.3, 0.5, 0.7, 0.9mL/L, respectively. The hydraulic diameters of rectangular microchannels used in the present work ranged from 0.3, to 1 mm. It was found out that the dimensionless liquid film thickness rises with the increasing hydraulic diameter of microchannels. Additionally, as the Ca increased, the dimensionless liquid film thickness exhibits initial growth before stabilizing.

References

[1] Bretherton F P .The motion of long bubbles in tubes[J].Journal of Fluid Mechanics, 2006, 10(2):166-188.DOI:10.1017/S0022112061000160.

[2] Aussillous P , Quere D .Quick deposition of a fluid on the wall of a tube[J].Physics of Fluids, 2000, 12(10):2367-2371.DOI:10.1063/1.1289396.

[3] Han Y , Shikazono N .Measurement of the liquid film thickness in micro tube slug flow[J].International Journal of Heat & Fluid Flow, 2009, 30(5):842-853.DOI:10.1016/j.ijheatfluidflow.2009.02.019.

Presenting Author: Dengwei Fu SUN YAT-SEN UNIVERSITY

Presenting Author Biography: Dengwei Fu is a master's student in the School of Physics and Astronomy at Sun Yat-sen University. His research primarily focuses on the measurement and analysis of liquid films thickness of gas-liquid Taylor flow in rectangular microchannels. He holds a bachelor's degree in Applied Physics from South China University of Technology. Proficient in both Chinese and English, he is known for his optimistic and proactive nature. If you find his research topics intriguing, please don't hesitate to reach out to him via email: fudw3@mail2.sysu.edu.cn

Authors:

Dengwei Fu SUN YAT-SEN UNIVERSITY
Sihui Hong Sun Yat-Sen University