Abstract
The purpose of this thesis is to investigate compressibility and rarefaction effect in micro gas flow by measuring pressure profiles in microchannel. Both of them have been sudied by using micro pressure sensors which are fabricated with the comventional MEMS technique in the past decades. The spatial resolution and low-pressure sensivity for conventional pressure sensors is not enough due to its size and membrance design. As a result, most of the studies discussing compressibility and rarefaction effect in microchannel were carried out by the numerical simulation. In this study, pressure-sensitive paints (PSP) and temperature-sensitive paint (TSP) are applied inside rectangular microchannel (0.5 cm x 50 μm/100 μm x 50 μm) to obtain the globl flow field with detailed pressure and temperature data. The spatial resolution for the PSP/TSP measurements has improved to 3.73 μm/ pixel by integrating a microscope with a 4X objective lens in the system to collect the luminescent signals. In order to improve the accuracy of PSP measurements, in-situ and pixel-by-pixel calibration are applied in data processing. Therefore, compressibility and rarefaction effects can be clearly observed in microchannel with the pressure data obtained by PSP measurements. Due to the temperature dependence of PSP sensors, the luminescent intensity of PSP sensors does not only change with pressure but also temperature variation. Hence, it’s nescessery to examine the temperature distribution inside the microchannel by TSP sensors. The result shows that the axial temperature along microchannel increases in contimuum flow regime; however, the temperature inceasement can be barly observed while the Knudsen number is greater than 0.001. Additionally, all the temperature defference inside the microchannel for each flow condition is less than 2.3 ℃. The difference of luminescent intensity of PSP (PtTFPP/ PDMS) is less then 1% in 2.3 ℃ temperature defference. Thus, the pressure distribution inside the microchannel can be obtained with PSP technique without temperature effect. In pressure measurements, the PSP results show that the nonlinear pressure distributions in microchannels which are caused by compressibility effect. The dimensionless deviation from the linear pressure distribution raised from 0.02 to 0.23, and the dimensionless location of the maximum deviation increased from 0.47 to 0.62 with increasing inlet to outlet pressure ratios from 1.9 to 4.6. On the contrary, rarefaction effect reduces the curvature of pressure distribution inside the microchannel as the Kudsen number increases. The dimensionless deviation from the linear distribution reduced to 0.07 from 0.25, and the dimensionless location of the maximum devication also decreased due to the gaseous slip at the wall as the outlet Knudsen number increased to o.oo8 from 0.006. According to the experimental results, compressibility effect and rarefaction effect restrain each other in microchannel in terms of nonlinearity of pressure distribution. In conclusion, the feasibility of PSP/TSP sensors in microchannel measurements has been demonstrated in this study. Compressibility and rarefaction effects in microscale have been discussed with the detail pressure information obtained by PSP technique. The PSP/TSP results are valuable for future gas-MEMS development.