Oxygen and nitrogen gases mixing in T-type micromixers visualized and quantitatively characterized using pressure-sensitive paint

This study investigated the mixing between oxygen and nitrogen gases in T-type micromixers by using the experimental technique known as pressure-sensitive paint (PSP). Both mixing qualities and flow fields for oxygen and nitrogen gases in T-type micromixers were quantitatively visualized in great detail. T-type micromixers with a width of 550 μm and a height of 125 μm were selected for the investigation. The mixing quality in a 10-mm-long mixing channel can reach 75% at the channel exit for Reynolds (Re) numbers of 13.9-36.7 [Peclet (Pe) numbers of 10.5-27.6]. Under these low Re and Pe conditions, mixing was dominated by diffusion and longer retention time resulted in higher mixing quality. When the Re number was set to 376.2 (Pe = 252.8), convection increased in the mixing channel, and the mixing quality dropped to 34.95% at channel exit. However, when the Re number was increased to 596.1 (Pe = 428.6), the engulfment flow regime was identified as an asymmetric flow pattern in the mixing channel. The mixing quality at a Re number of 596.1 was approximately 30% higher than that at a Re number of 376.2. Commercial CFD software, ANSYS CFX, was used to simulate the flow fields inside the T-type micromixers, and the numerical data was compared with experimental PSP measurements. Favorable agreement has been established for the cases measured before the engulfment flow regime started. In addition, the flow fields and mixing quality levels of oxygen and nitrogen gases with asymmetric inlet conditions were obtained. The asymmetric flow pattern, which was similar to the engulfment flow regime, was triggered more easily, and an agitated flow improved the mixing quality in the T-type micromixers. The feasibility of PSP measurement in microscale gas mixing was demonstrated and validated in this study. Future studies can experimentally investigate micromixer designs by using various active or passive actuators to obtain detailed information regarding flow fields and the evolution of mixing quality.