EFFECTS OF OBSTACLES ON THE MIXING PERFORMANCE IN MICROCHANNELS

摘要

The mixing of two or more fluid streams in microchannels needs quite long channel lengths. Therefore, in order to improve the mixing performance, obstacles have been placed in the channel to disrupt flow and to reduce the diffusion path. The disruption to flow velocity field alters the flow direction from one fluid to another. Properly designed geometric parameters, such as layout, angle with main flow direction and aspect ratio of obstacles, will be resulted in improving the mixing performance with only little increase of the pressure drop. In this study, T-type rectangular microchannel is used, which has two inlets with W×H×L=100×100×1000 μm~ and one outlet with W×H×L=200× 100×6950 μm~3. Furthermore, the mixing channel has obstacles which are placed with an angle of inclination and with dimensions W×H×L=10×100×h μm~3 on the lower layer. In order to estimate the performance of the mixing, numerical analyses are carried out with water and ethanol. Especially, the diffusion coefficient, D , is set to 10~(-10) m~2/s for simulating two-fluid diffusion-convection flow, the mixing efficiency and the pressure drop of microchannel are investigated with various values of the angle of inclination, aspect ratio (h=αH) of obstacle and Reynolds number. When the flow passes through on the obstacles, rotation flow is observed. This flow pattern is repeated at each cycle. Besides, in each case that obstacles are turned to the center of channel and to the side walls, rotational direction is changed reversely. In case of pressure drop, as the Reynolds number, the angle of obstacle (θ) and the aspect ratio (α ) are increased, the pressure drop is also increased. Results show that the ratio between the maximum and minimum of pressure drop is the order-of-magnitude of 1 at Re= 1.667. Results also show that the angle of inclination of obstacles has more influence on the mixing performance than the height of obstacles and Reynolds number.