Abstract
This study aims to apply Pressure-Sensitive Paint technique to various 90 degree elbow microchannels in order to measure two dimensional pressure distributions and perform analysis in Reynolds number range from 88 to 442. Different designs of 90 degree elbow microchannels are investigated in this study including sharp turn 90 degree microchannels with different channel widths and depths, a double turn elbow microchannel and a round turn microchannel. A 4X and a 10X objective lenses are used to capture the luminescent signals inside the microchannels, and these lenses can deliver magnification of images of 3.7 μm and 1.5 μm per pixel spatial resolution. During the investigation of sharp turn microchannel, two microchannels with different widths are studied. From the global pressure distributions acquired from microchannel inlet to exit, significant pressure differences are observed at the locations between before the turn and after the turn in the microchannel with 400 μm width, which cannot be identified in the microchannel with 200 μm width. In local pressure measurement around the corner, threre is a high pressure zone near the outside wall of corner and also a low pressure region at the inner wall downstream after the corner. As for study with different depths of microchannels, the sharp microchannels with 200 μm depth and 100 μm depth have the same trend which are like the results acquired in the microchannel with 400 μm width,. For different elbow designs of double turn and round turn, there are two high pressure zones obersved in double turn microchannel near each 45 degree turn. There is a high pressure region continuously developing around the outside wall of round turn microchannel at different Reynolds conditions. In order to compare the pressure loss in different cases which is considered as minor loss of energy, the equation calculating equivilent length for the 90 degree turns in the microchannel flow is used. For the microchannel flow with 90 degree sharp turn, the minor loss increases as the Renolds number comes larger. If the Reynolds number is greater then 200, the minor loss estimated in the microchannel with 400 μm width becomes larger than the one with 200 μm width, and the minor loss is always greater if the depth of microchannel is bigger. From the experimental results acqruied in this study with different designs of 90 degree elbow microchannel flows, the physical phenomena of flow patterns in such devices become clearer.