[기계] Prof. Phil Ligrani  세미나 공지

1. 제 목 : SLIP PHENOMENA IN GASES AND A NEWTONIAN LIQUID
as Investigated Within a Micro-Scale Viscous Disk Pump
2. 연 사 : Professor Phil Ligrani
Professor of Aerospace and Mechanical Engineering, Oliver L. Parks Endowed
Chair in Engineering
Parks College of Engineering, Aviation, and Technology, Saint Louis Univ.

3. 일 시 : 2010년 10월 7일 (목요일)  16:00~17:00

4. 장 소 : 301동 1512-2호

5. 내 용 :
Slip phenomena are investigated in two different sets of experiments conducted in gases and one Newtonian liquid. Overall, differences in near-surface slip behavior are illustrated for these two different fluid mediums, where the slip is induced surface roughness and rarefaction in the gases, and by surface roughness and intermolecular interactions in the liquid.

Within the gas experiments, flows are induced by rotation within C-shaped fluid chamber passages formed between a rotating disk and a stationary surface. Accommodation coefficients are determined in a unique manner from experimental results and analysis based on the Navier-Stokes equations. The fluid chamber passage height ranges from 6.85 m to 29.2 m to give Knudsen numbers from 0.0025 to 0.031 for air and helium. In all cases, roughness size is large compared to molecular mean free path. When channel height is defined at the tops of the roughness elements, slip is believed to be a result of rarefaction as well as fluid shear. With this arrangement, tangential accommodation coefficients decrease and slip velocity magnitudes increase, at a particular value of Knudsen number, as the level of surface roughness increases. When channel height is defined midway between the crests and troughs of the roughness elements, non-dimensional pressure rise data show little or no dependence upon the level of disk surface roughness and working fluid. In addition, slip is largely independent of surface roughness magnitude and mostly due to rarefaction.
 
With Newtonian water as the working fluid, hydrophobic roughness is used to induce near-wall slip in the single rotating-disc micro-pump. The amount of induced slip is again altered by employing different sizes of surface roughness on the rotating disk. The magnitudes of slip length and slip velocities increase as the average size of the surface roughness becomes larger. Comparisons with analytic results, determined from the rotating Couette flow forms of the Navier-Stokes equations, show that slip length magnitudes show significant dependence on radial-line-averaged shear stress for average disk roughness heights of 404 nm and 770 nm. The resulting slip length data show a high degree of organization when normalized using by either the average roughness height or the fluid chamber height. With the latter arrangement, experimental data obtained using different chamber heights and different disk roughness magnitudes collapse along a single line, illustrating strong linear dependence of the slip length on the normalized radial-line-averaged shear stress. Increasing near-wall slip magnitudes are then associated with reduced pressure rise through the pump and lower radial-line-averaged shear stress magnitudes (determined within slip planes), which is the same qualitative trend of behavior which would result if intermolecular interactions associated with micro-scale phenomena are present.

6. 문 의 : 기계항공공학부 이준식 교수 (☏7123 )