Abstract
Microchannels are an integral part of various micro devices i.e. micro chemical reactors, fuel cell and electronic packaging etc. There are two important criteria for design of microchannels. The first criterion is the minimization of pressure drop across the microchannel such that the parasitic power requirement is minimized during the operation of these devices. The second criterion is the mixing enhancement due to stronger wall-normal motion of the near wall fluid particles leading to reduction in velocity, temperature and concentration gradient at the wall. Wall surface roughness can be suitably modified for achieving the above objectives in macro-scale flows. Riblets on the channel surface are effective in reducing the frictional resistance for macro flow situations. Various ribs or turbulator geometries have proved to be effective for near wall mixing in heat exchangers and gas turbine blade cooling ducts. However, no systematic study on mixing enhancement due to flow past repeated micro ribs inside microchannel is available in literature. The present study presents the detailed flow past repeated micro-ribs inside a microchannel from micro-PIV (Particle Image Velocimetry) measurements. The microchannel made of Polydimethylsiloxane (PDMS) has been fabricated by PDMS replica moulding. The channel is 50 mu m x 120 mu m cross section. The width and height of ribs are 30 mu m and 1% mu m respectively. The pitch between the multiple ribs is equal to 100 mu m. The presence of flow separation at the edge of the rib with generation of vortex structure is not observed at the flow rate set in the present study contrary to the macro flow situations. However, the shear layer is deflected towards the wall with increase in wall-normal velocity indicating possible effectiveness of micro ribs for mixing enhancement in the microchannels.