Abstract
This study aims to apply pressure sensitive paint (PSP) technique in constricted microchannel flow. The asymmetric flow with two-dimensional and global flow fields has been measured successfully. The constricted microchannel flow has been studied by using micro pressure sensor fabricated with the conventional MEMS technique. Due to the arrangement of micro pressure sensor, only one-dimensional pressure distribution was acquired and pressure drop around constriction was detected. Asymmetric flow behavior was not observed using conventional MEMS pressure sensors. Thus, the study of the global pressure profile in constricted microchannel flow was almost executed by the numerical simulations. PSP is a technique using optical chemical reaction of luminescent molecules to provide the pressure/temperature data in experiments. Additionally, it can provide global flow field with detailed pressure and temperature data. ANSYS CFX has been used to simulate the flow field in microchannel. While the constricted ratio (CR) greater than 5, the asymmetrical flow can be observed in simulation results. The pressure difference at lateral locations is 2 kPa due to the flow separation. Before applying PSP sensor in current study, the temperature dependence of PSP sensor has been examined. The intensity of PSP sensor not only changes with pressure, but also temperature. The temperature distribution inside a constricted microchannel (CR=5) has been measured. The result shows that the temperature difference through the ribs is around 3.5℃ at Re=121. The response of PSP sensor (PtTFPP/PDMS) does not change much in such temperature difference. Thus, PSP technique still can reveal the flow fields inside the constricted microchannel in current study. In order to increase the spatial resolution of experimental data and eliminate the shadow effect caused by inclined light source, a microscope with a 4X and a 10X objective lens is used to collect the luminescent signals. Pixel-by-pixel calibration and in-situ calibration have been used to improve the accuracy of PSP sensor measurements. The constricted microchannel flow with higher CR ratio (CR=5), the pressure difference between lateral locations (±0.15 W) is 2.5 kPa at Re=279 and 1.2 kPa at Re=107. Overall, with the understanding of constricted microchannel flow provided by the PSP technique, the application of the constricted microchannel can be further extended to the design of MEMS devices like micro mixers.