Research Papers

A Numerical Study of Droplet Splitting and Merging in a Parallel-Plate Electrowetting-on-Dielectric Device

[+] Author and Article Information
Yin Guan

Department of Mechanical
and Aerospace Engineering,
University of Texas at Arlington,
Arlington, TX 76019
e-mail: yin.guan@mavs.uta.edu

Albert Y. Tong

Department of Mechanical
and Aerospace Engineering,
University of Texas at Arlington,
Arlington, TX 76019
e-mail: tong@uta.edu

Manuscript received April 28, 2014; final manuscript received March 23, 2015; published online May 14, 2015. Assoc. Editor: Yogesh Jaluria.

J. Heat Transfer 137(9), 091016 (Sep 01, 2015) (11 pages) Paper No: HT-14-1256; doi: 10.1115/1.4030229 History: Received April 28, 2014; Revised March 23, 2015; Online May 14, 2015

Microwater droplet splitting and merging in a parallel-plate electrowetting-on-dielectric (EWOD) device have been studied numerically. 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 (LS) 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 results of the numerical model have been validated with published experimental data and the physics of droplet motion within the EWOD device has been examined. A parametric study has been performed in which the effects of channel height and several other parameters on the fluid motion have been studied.

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Fig. 1

(a) Top and (b) cross-sectional views of the EWOD device

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Fig. 2

Contact angle saturation effect [11]

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Fig. 3

Pressure difference induced by electrical actuation

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Fig. 4

Contact angle hysteresis effect. θS, θR, and θA are static, receding, and advancing contact angles, respectively

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Fig. 5

Flow chart of the CLSVOF scheme: coupling process in the dashed box

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Fig. 6

Computational domain for droplet splitting

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Fig. 7

Droplet splitting: numerical (top: present study) and experimental (bottom: ([14])

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Fig. 8

Flow fields of droplet splitting at selected instants: (a) 66.7 ms; (b) 128.7 ms; and (c) 133.3 ms

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Fig. 9

Pressure fields of droplet splitting at selected instants: (a) 66.7 ms; (b) 128.7 ms; and (c) 133.3 ms

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Fig. 10

Droplet merging: numerical (top: present study) and experimental (bottom: ([14])

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Fig. 11

Flow fields of droplet merging at selected instants: (a) 90.0 ms; (b) 101.0 ms; and (c) 127.0 ms

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Fig. 12

Pressure fields of droplet merging at selected instants: (a) 90.0 ms; (b) 101.0 ms; and (c) 127.0 ms

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Fig. 13

Droplet splitting with formation of a satellite droplet at 0.035 mm channel height

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Fig. 14

Droplet splitting time versus channel height

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Fig. 15

Droplet splitting with 0.15 mm channel height

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Fig. 16

Droplet transport time before merging versus channel height

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Fig. 17

Droplet merging with 0.60 mm channel height

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Fig. 18

Parametric study: splitting (top) and merging (bottom)

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Fig. 19

Droplet splitting with different grid sizes: 0.05 × 0.05; 0.025 × 0.025; and 0.0125 × 0.0125




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