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Research Papers: Heat and Mass Transfer

# Mesoscopic Analysis of Dynamic Droplet Behavior on Wetted Flat and Grooved Surface for Low Viscosity Ratio

[+] Author and Article Information
Saurabh Bhardwaj

Department of Mechanical Engineering,
Indian Institute of Technology Guwahati,
Guwahati, Assam 781039, India

Amaresh Dalal

Department of Mechanical Engineering,
Indian Institute of Technology Guwahati,
Guwahati, Assam 781039, India
e-mail: amaresh@iitg.ernet.in

1Corresponding author.

Presented at the 2016 ASME 5th Micro/Nanoscale Heat & Mass Transfer International Conference. Paper No. MNHMT2016-6492.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received June 14, 2016; final manuscript received February 20, 2017; published online March 7, 2017. Assoc. Editor: Zhuomin Zhang.

J. Heat Transfer 139(5), 052002 (Mar 07, 2017) (11 pages) Paper No: HT-16-1380; doi: 10.1115/1.4036036 History: Received June 14, 2016; Revised February 20, 2017

## Abstract

In the present study, the interfacial dynamics of displacement of three-dimensional spherical droplet on a rectangular microchannel wall considering wetting effects are studied. The two-phase lattice Boltzmann Shan−Chen model is used to explore the physics. The main focus of this study is to analyze the effect of wettability, low viscosity ratio, and capillary number on the displacement of spherical droplet subjected to gravitational force on flat as well as grooved surface of the channel wall. The hydrophobic and hydrophilic natures of wettabilities on wall surface are considered to study for viscosity ratio, $M≤1$. The results are presented in the form of temporal evolution of wetted length and wetted area for combined viscosity ratios and wettability scenario. In the present study, it is observed that in dynamic droplet displacement, the viscosity ratio and the capillary number play a significant role. It is found that as the viscosity ratio increases, both the wetted area and the wetted length increase and decrease in the case of hydrophilic and hydrophobic wettable walls, respectively. The groove area on the vertical wall tries to entrap fraction of droplet fluid in case of hydrophilic surface of the vertical wall, whereas in hydrophobic case, droplet moves past the groove without entrapment.

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## Figures

Fig. 1

(a) Schematic diagram of computational domain and (b) D3Q19 lattice model

Fig. 2

Fig. 3

Variation of contact angle with g2w

Fig. 4

Dynamic droplet behavior under gravity with different lattice times at Ca = 0.35, g2w=0.05, and viscosity ratio ((a) M = 0.7, (b) M = 0.8, and (c) M = 0.9)

Fig. 5

The shape of the droplet in y–z plane at x=40 lu (i.e., (a)–(c)) and x–z plane view at wall (i.e., (d)–(f)) for Ca = 0.35, g2w=0.05, lattice time = 8, and viscosity ratio ((a) M = 0.7, (b) M = 0.8, and (c) M = 0.9)

Fig. 6

Effect of viscosity ratio at Ca = 0.35 and g2w = 0.05: (a) time evolution of wetted area and (b) time evolution of wetted length

Fig. 7

The shape of the droplet in y–z plane at x=40 lu (i.e., (a)–(c)) and x–z plane view at wall (i.e., (d)–(f)) for Ca = 0.35, g2w=−0.02, lattice time = 20, and viscosity ratio ((a) M = 0.7, (b) M = 0.8, and (c) M = 0.9)

Fig. 8

Effect of viscosity ratio at Ca = 0.35 and g2w = −0.02: (a) time evolution of wetted area and (b) time evolution of wetted length

Fig. 9

The shape of the droplet in x z plane view at wall for g2w=0.05, lattice time = 8, viscosity ratio, M = 0.8, and (a) Ca = 0.1, (b) Ca = 0.35, and (c) Ca = 0.66

Fig. 10

Schematic of the computational domain of grooved surface vertical wall

Fig. 11

Dynamic droplet behavior under gravity with different lattice times on grooved wall at Ca = 0.1, g2w=−0.02, viscosity ratio, M = 1, and at different lattice times

Fig. 12

Dynamic droplet behavior under gravity with different lattice times on grooved wall at Ca = 0.35, g2w=−0.02, viscosity ratio, M = 1, and at different lattice times

Fig. 13

Dynamic droplet behavior under gravity with different lattice times on grooved wall at Ca = 0.66, g2w=−0.02, viscosity ratio, M = 1, and at different lattice times

Fig. 14

Dynamic droplet behavior on grooved wall with different lattice times at Ca = 0.35, groove height = 20 lu, g2w=−0.02, and nondimensional time ((a) t = 14.06, (b) t = 17.19, (c) t = 20.31, and (d) t = 23.44)

Fig. 15

Dynamic droplet behavior on grooved wall with different lattice times at Ca = 0.35, groove height = 40 lu, g2w=−0.02, and nondimensional time ((a) t = 14.06, (b) t = 17.19, (c) t = 20.31, and (d) t = 23.44)

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