TURBULENT FLOW IN A MICROCHANNEL WITH SURFACE PATTERNED MICRORIBS ORIENTED PARALLEL TO THE FLOW DIRECTION

摘要

Due to the increase of application in a number of emerging technologies, a growing amount of research has focused on the reduction of drag in microfluidic transport. A novel approach reported in the recent literature is to fabricate micro-ribs and cavities in the channel wall that are then treated with a hydrophobic coating. Such surfaces have been termed super- or ultrahydrophobic and the contact area between the flowing liquid and the solid wall is greatly reduced. Previous numerical studies have focused primarily on the laminar flow through such channels with reductions in the flow resistance as large as 87% being predicted and observed. There has been little work however, that has explored the physics and the potential drag reduction associated with turbulent flow through microchannels with ultrahydrophobic walls. This paper reports the results of a numerical investigation of the turbulent flow in a parallel plate microchannel with ultrahydrophobic walls. In this study micro-ribs and cavities are oriented parallel to the flow direction. The channel walls are modeled in an idealized fashion, with the shape of the liquid-vapor meniscus approximated as flat. A k-ω turbulence modeling scheme is implemented for closure to the turbulent RANS equations. Results are presented for the friction factor Reynolds number product as a function of relevant governing dimensionless parameters. The Reynolds number was varied from 2,000 to 10,000. Results show, as with the laminar flow case, that as the shear-free region increases the friction factor-Reynolds number product decreases. The observed reduction, however, was found to be significantly greater under turbulent flow conditions than for the laminar flow scenarios.