Portland State University. Department of Mechanical and Materials Engineering
Date of Publication
Doctor of Philosophy (Ph.D.) in Mechanical Engineering
Microfluidics, Separation (Technology), Liquids, Fluid mechanics
i online resource (xiii, 198 pages)
Fluid mixtures in real life exist in two forms: miscible and immiscible. Separation of these mixtures using chemical agents or thermal energy has both environmental and economic disadvantages. The high cost and the environmental damage caused by the traditional separation techniques have stimulated both academia and industry to seek alternatives. The emergence of microfluidics offers robust solutions for a broad span of transport problems due to the high surface to volume ratio and reduced length scales. Particularly, the separation efficiency increases significantly due to the aforementioned feature. However, there is still a pressing need of passive separations for the sake of energy minimization and environmental safety. This work focuses on passive separation of both miscible and immiscible mixtures through the surface forces in microchannels. In the miscible case two fluids of physical properties imitating those of water and ethanol are investigated using the multi-range multi-components Shan-Chen Lattice Boltzmann Method (LBM) for a 2D channel. The variations of the fluid-fluid and fluid-solid interaction coefficients of both fluids, the relaxation times, and the spacing between the walls are examined under static conditions. The uneven interactions are considered with static as well as flow conditions. Because the surface forces are of intermolecular nature, their spacial range is short and did not exceed 30nm in our study. Therefore, we added solid posts distributed in patterns. The addition of these features enhanced the density jumps significantly between the upper and lower halves of the channel. In the immiscible case we studied how uneven wetting conditions influence two-phase flow in a 3D T-shaped microchannel. The D3Q27 LBM model with Shan-Chen forcing was used to control the contact angles of the lower and upper halves of the channel separately. The feasibility of separation was examined by constructing the breakup and non-breakup regimes for capillary numbers (Ca) ranging from 0.002 to 0.3 and droplet lengths (L0) ranging from 1.5 to 4 times the width of the channel (W = 30µm). The difference between the upper and lower contact angles has the strongest impact on the breakup and non-breakup regimes. The geometrical parameters represented by the main channel aspect ratio (AR) and side to main channel width ratio (WR) are also significant players as they shift the border of the breakup area significantly.
Radhi, Mohanad Kamil, "Passive Separation of Binary Fluid Mixtures in Microchannels Using Lattice Boltzmann Method" (2019). Dissertations and Theses. Paper 5332.