Session: 12-21-01: Multiphase Flow

Paper Number: 173771

Fluorescent Axial-View Visualziation of Two-Phase Flows 

A novel method is proposed for an axial viewer to observe two-phase flow within a tube and directly measure both void fraction and annular film thickness through the use of fluorescent illumination. Two-phase flow, and more specifically, annular flow, is a common phenomenon that takes place within a variety of engineering applications, including nuclear reactors, HVAC, and electronics cooling. The heat transfer during this flow is highly dependent on many variables, some of which can be measured directly through observation of the flow. Various methods have been proposed to observe these phenomena, such as side viewing and axial viewing of the test section. Previous studies which employed side viewing rather than axial viewing have shown good results in being able to observe the flow without disturbing it. However, this method has limitations, such as the inability to show clear, unambiguous interfaces due to curvature, light reflection and refraction, and interfacial waves, thus hindering flow observation fidelity. Additionally, it cannot show the circumferential distribution of film thickness, which is critical for the advancement of understanding of the flow patterns within two-phase flow, as well as quantifying the effects of gravity in larger diameter tubes. Finally, in cases of bubbly flow or liquid entrainment, it cannot show the radial distribution and motion of bubbles or droplets. An axial viewing system eliminates these problems. The solution presented will allow direct measurement of the void fraction and annular film thickness, as well as better visualization of the flow patterns. The proposed axial viewer is based on previous designs of an axial viewer. It employs a layer of pressurized air in front of the viewing glass to prevent fluid droplets from condensing and obstructing the view, and a passage around the viewing glass to divert the liquid phase. The main difference in this design compared to others is that the fluid under observation is doped with a fluorescent additive which illuminates under a laser. The addition of this fluorescence in the fluid allows a laser sheet to illuminate a thin cross section within the test section of the experiment. With illumination, a high-speed camera is able to take a picture through the axial viewer, allowing a clear image of the cross-section which can be used to determine void fraction and the film thickness at any point on the circumference. Currently, it is difficult to directly measure the geometry within two-phase flow without utilizing indirect measurement techniques or correlations. Successful development of this axial viewer would enable more accurate measurements and clear observation of phenomena during two-phase flow, and more specifically, annular flow. Anticipated results are the ability to capture clear images of the illuminated cross section with a high-speed camera. This allows the image to undergo post-processing which allows for the calculation of the void fraction and film thickness of the annular flow at a discrete position. This information can later be used in heat transfer coefficient calculations, completely avoiding the use of void fraction correlations, and increasing the quality and accuracy of the predictions.

Presenting Author: Chase Yankowski University of Maryland, College Park

Presenting Author Biography: Chase is a Ph.D. student in the University of Maryland, College Park. He received his B.S. in Mechanical Engineering from the University of Wisconsin-Madison in December 2023, and worked in the nuclear industry for a year afterwards.

Authors:

Chase Yankowski University of Maryland, College Park
Henry Gagliardi University of Maryland, College Park
Zachary Yashar University of Illinois Urbana-Champaign
Lingnan Lin University of Maryland, College Park