(168q) EFFECTS of Hydrophobicity-INDUCING Roughness ON MICRO-Flows

In this study, the effect of three-dimensional roughness on pressure-driven flow of water through a micro-channel is examined. A three-dimensional finite volume numerical model is used to analyze these effects (utilizing FLUENT). Specifically, the pressure drop between the inlet and outlet of the channel is analyzed and compared to relationships found in previous studies [1]. In the case of roughness created by the presence of micro-posts on the channel walls, the pressure drop is found to increase as a function of the height of the micro-posts. However, in the case where the space between the micro-posts is free of shear, (for example, when air or vapor bubbles are trapped between the micro-roughness elements) the pressure drop decreases. This would be a model of the well known case of super-hydrophobic surfaces, such as the lotus leaf surface [2]. The width of the microchannel is 5 micrometers and the height of the microposts ranges from 0.1 to 2 micrometers.

The presentation will discuss the development and validation of the computational model, as well as the effects of surface roughness combined with the effect of free shear between the microposts on the pressure drop through the microchannel. It is found that the pressure drop needed to sustain a particular flow rate can be smaller than that needed for a smooth microchannel, when the space between roughness elements is free of shear, i.e., corresponding to the case of air bubbles trapped in that space. Effects of roughness size and spacing will also be discussed.

Literature cited [1] Hu, Y., Werner, C., and Li, D., 2003, ?Influence of three-dimensional roughness on pressure-driven flow through microchannels,? J. of Fluids Engineering, 125, pp. 871-879. [2] Voronov. R.S., Papavassiliou, D.V., Lee, L.L., 2008, ?Review of fluid slip over superhydrophobic surfaces and its dependence on contact angle, Ind. Eng. Chem. Res., 47, pp. 2455-2477