Experimental Study of Microbubble Formation in Micro Channel

The formation of unconfined spherical microbubbles in a micro channel is investigated in this study. A liquid channel (primary channel) and a gas channel (secondary channel) which is perpendicular to each other form a T-Junction where the microbubbles are formed. Fused silica tubes of 20μm inner diameter and 360μm outer diameter is used as the secondary channel. The hydraulic diameter of the liquid channel is varied to study its effect on the bubble formation. Because of the small size of the gas orifice compared to the hydraulic diameter of the liquid channel the microbubbles formed are completely spherical, thus giving enough facility to study its formation and detachment criteria. The microbubble formation inside the micro channel is studied subjected to variable parameters such as liquid flow rate, gas flow rate, and the hydraulic diameter of the liquid channel. Silicon wafer subjected to dry etching techniques is used to make both the primary micro channels and channels which holds the fused silica tube (secondary channel). A glass piece is anodically bonded to the silicon wafer which seals both the channel from the top. Holes are drilled on to the glass piece to provide the inlet and outlet of the channels and the T-junction is continuously monitored using an Olympus i-speed camera capable of taking 10000 frames per second. Di ionized water is used as the liquid and nitrogen is used as the gas for bubble formation. The results obtained show that the bubble diameter decreases with the increase in the liquid flow rate, and decrease in hydraulic diameter of the liquid channel. The gas flow rate does not have any effect on the bubble diameter, as the gas flow rate was increased the frequency of the bubble formation increases.