Peer ReviewedPostprint (published version

We perform a quantitative characterization of a microbubble injector in conditions relevant to microgravity. The injector pregenerates a slug flow by using a capillary T-junction, whose operation is robust to changes in gravity level. We address questions regarding the performance under different injection conditions. In particular we focus on the variation of both gas and liquid flow rates. The injection performance is characterized by measuring bubble injection frequency and bubble sizes. We obtain two distinct working regimes of the injector and identify the optimal performance as the crossover region between them.

We present an analysis of the geometry of the continuous and disperse phases in the bubble and slug flow regimes in air–water mixtures generated in a capillary T-junction of 1 mm internal diameter. Bubble size dispersion is very low in the considered flow patterns. The concept of unit cell is used to identify two characteristic lengths of the two-phase flow, namely, the unit cell length and the bubble length. The relationship between these lengths and the gas and liquid superficial velocities, gas mean velocity, bubble generation frequency and volume average void fraction is analysed. We conclude that in the considered\ud configuration the unit cell and bubble lengths can be predicted either by the ratio of the gas–liquid\ud superficial velocities or the volume average void fraction.Peer ReviewedPreprin

We perform a characterization of a recently reported minibubbles (bubbles with a diameter of the order of 10‐3 m)\ud generator in microgravity related conditions. Generation of bubbles is based on the generation of a slug flow in a capillary\ud T‐junction, whose operation is robust to changes in the gravity level. We address questions regarding the performance\ud under different working regimes. In particular, we focus on the regimes found within a large range of gas and liquid\ud injection flow rates. The injection performance is characterized by measuring bubble generation frequency. We propose\ud curves obtained empirically for the behavior of generation frequency and crossover between regimes.Peer ReviewedPostprint (author’s final draft

This paper presents a three-dimensional numerical study of the bubble generation process in a micro T-junction, performed with the commercial computational fluid dynamics solver ANSYS Fluent, version 15.0.7. Numerical results on the bubble generation frequency, bubble velocity, volume void fraction, bubble volume, and characteristic bubble lengths are compared with experimental data. Additionally, a new simple fitting for the bubble generation frequency, based upon previously reported experimental works, is proposed here.