Fluid mechanics of flow through microchannels

Abstract

The main objective of this thesis is to characterize and investigate single-phase liquid flow in microchannels, and can be divided into two parts: analytical modeling and experimental investigation. In the analytical part, velocity distribution and Darcy friction factor of liquid flow in both parallel-plate and rectangular microchannels were revised theoretically by taking into account the effects of slip boundary conditions as well as the aspect ratio of the channels.

The combined effects of changing relative spacing, eccentricity, and viewing directions on the wetting conditions of the fabricated micropillar surfaces were experimentally investigated. The equilibrium 3D shape of the droplet on anisotropic surfaces was also examined. The wettability of microhole structures fabricated by replica molding of polydimethylsiloxane (PDMS) was analyzed by measuring both static and dynamic contact angles and it was found that wetting conditions can be controlled not only by changing the normalized widths but also the eccentricities. Generally, increasing the micropattern eccentricity increased the contact angle hysteresis. Dependency of the contact angle hysteresis on microhole eccentricity was explained by the shape of the three-phase contact line on microhole configurations. Drag reduction of microchannels with microhole arrays efficiency was evaluated. The results indicated that the impact of microhole eccentricity on drag reduction performance correlated well with the contact angle hysteresis, rather than the static contact angle. These findings provide additional insights in design and fabrication of efficient micropatterned channels for reducing the flow resistance.