Yin Guan

Graduation Semester and Year

2015

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Aerospace Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Albert Y. Tong

Abstract

Microscale water droplet motions in parallel-plate electrowetting-on-dielectric (EWOD) devices including transport, splitting, merging and dispensing have been numerically studied. The transient governing equations for the microfluidic flow are solved by a finite volume scheme with a two-step projection method on a fixed computational domain. The interface between liquid and gas is tracked by a coupled level set and volume-of-fluid (CLSVOF) method. A continuum surface force (CSF) model is employed to model the surface tension at the interface. Contact angle hysteresis which is an essential component in EWOD modeling is implemented together with a simplified model for the viscous stresses exerted by the two plates at the solid-liquid interface. The accuracy of the numerical model has been validated with published experimental data and excellent agreement has been achieved between the numerical and experimental results for all four operations. The physics of droplet motions within the parallel-plate EWOD devices has been thoroughly examined. For the transport process, special attention has been focused on some localized areas near the ON/OFF electrode border where the transport process is primarily influenced. A dimensionless curvature has been introduced and a critical value has been identified beyond which the droplet would split during the transport. A parametric study has been performed in which the effects of several crucial parameters including initial droplet shape, static contact angles, contact angle hysteresis, viscous stress, channel height and electrode size on the transport process have been revealed. For the splitting and merging processes, a parametric study has been performed in which the effect of channel height and droplet physical properties on the droplet motions has been investigated. The dispensing process of micro droplets in parallel-plate EWOD devices with various reservoir designs has been simulated. The dispensing mechanism has been carefully examined and droplet volume reproducibility for each design has been investigated. Several key elements which directly affect volume reproducibility have been identified.

Disciplines

Aerospace Engineering | Engineering | Mechanical Engineering

Comments

Degree granted by The University of Texas at Arlington

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