Effects of momentum flux and separation distance on bubbly jet impingement in microgravity conditions

• The angle of the non-interacting jets decreases as the momentum flux is increased.
• Impinging jets evolve in time from independent conical shapes to cross-like shapes.
• A decrease in the bubble velocity has been observed in the impingement zone.
• Smaller bubbles are obtained at higher values of the momentum flux.
• More coalescences events occur in microgravity compared to the results on ground.

The characteristics of two impinging bubble jets have been experimentally studied in microgravity conditions. The experimental setup, designed to be used in a drop tower, allows to change the gas and liquid flow rates for the jet generation, and the separation distance between the jets. A slug flow with millimetric air bubbles is created in a T-junction and injected through a nozzle in a water tank. The formation and dynamics of the generated bubble jets have been recorded by means of a high-speed camera. The effects of the momentum flux and the separation distance on the two-phase flow have been investigated. When jets do not interact, they show a conical shape with an opening angle which decreases from Ψ=63°Ψ=63° to Ψ=12°Ψ=12° as the momentum flux is increased from J=1gcm/s2 to J=88gcm/s2. Bubble velocities in the direction of injection decrease from vx=361cm/s to vx=23cm/s in the most extreme case, as the bubble center position reaches the impingement region. Interacting bubble jets form a cross-like shape as the jets evolve in time. Bubble mean diameter decreases from d¯=1.7 cm to d¯=1.3 cm, as the momentum flux increases from J=8gcm/s2 to J=43gcm/s2. Coalescence events, occurring mainly near the nozzles and in the impingement region, are responsible for the widening of the tail in the bubble size distribution. The global jet behavior and the individual bubble dynamics present several differences in microgravity compared to previous observations carried out on ground.