The experimental characterization of two-phase flow regimes inside the mixing chamber of an effervescent atomizer is studied.Air was injected into a liquid water cross-flow through a single orifice located at the conduit wall of a horizontally oriented,outside-in atomizer.The atomizer had a square conduit with transparent walls to obtain full,undistorted visualization of the interaction between the gas and liquid near the injector area.The volumetric liquid flow rates ranged between 0.15 and 0.70 LPS while the gas mass flow rates were varied from 0.25 to 3.00 SLPM; this resulted in gas to liquid mass ratio(GLR)values ranging from 0.01-0.25.Three different nozzle injector diameters(0.27,0.52 and 1.59 mm)were used to observe the effect on the bubbling regimes.The operating conditions were constrained to the bubble flow case.The study was conducted with the use o f high-speed shadowgraphy.Three markedly different regimes were identified: Single Bubbling,Pulsating and Jetting.Two clearly defined sub-regimes were observed within the Jetting mode: Elongated Jet and Atomizing Jet.The results obtained were grouped in the form of bubbling charts,constructed by mapping the regimes in dimensionless Cartesian coordinates,the liquid phase Reynolds number in the abscissa and the gas jet Reynolds number in the ordinate axis.These maps constitute an unexplored design alternative that highlights the importance of the bubble formation conditions on the performance of an effervescent atomizer.