Renato Rosa Oliveira

Abstract

This work presents an experimental study on the hydrodynamics of Taylor bubbles rising in a vertical rectangular mini-channel with a cross-section of 2×5 mm, using air and water as working fluids. This flow regime is of particular interest for the thermal management of Small Modular Reactors (SMRs) and microelectronic devices, where the stability of the thin liquid film surrounding the bubble governs heat transfer performance. The primary objective was to characterize the liquid film thickness and bubble velocity under adiabatic conditions, covering Capillary numbers (Ca) between 10 −4 and 10 −3 and Reynolds numbers (Re) ranging from 80 to 600. A synchronized optical diagnostic setup was developed, combining high-speed shadowgraphy to capture macroscopic bubble kinematics and white-light interferometry (spectrometry) to measure the micrometric liquid film thickness with high temporal resolution. The interferometric technique was validated using a reference Indium Tin Oxide (ITO) sample. Experimental results showed bubble velocities ranging from 0.03 to 0.22 m/s and film thicknesses between 5.8µm and 22.2µm. The measured film thicknesses were compared against established semi-empirical correlations for circular and non-circular conduits. The data showed excellent agreement with the correlation proposed by Magnini et al. (2022) for rectangular geometries, ix demonstrating the significant influence of corner drainage and channel aspect ratio on film dynamics, which are not captured by classical circular-tube models

Advising

Advisors: Anjos, G. R.; Tecchio, Cassiano