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Research Papers: Multiphase Flows

Wall Effects on the Brownian Movement, Thermophoresis, and Deposition of Nanoparticles in Liquids

[+] Author and Article Information
Efstathios E. Michaelides

Department of Engineering,
Texas Christian University,
Fort Worth, TX 76132
e-mail: E.Michaelides@tcu.edu

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received June 8, 2015; final manuscript received November 11, 2015; published online January 8, 2016. Editor: Malcolm J. Andrews.

J. Fluids Eng 138(5), 051303 (Jan 08, 2016) (7 pages) Paper No: FE-15-1388; doi: 10.1115/1.4032030 History: Received June 08, 2015; Revised November 11, 2015

It is well known that the hydrodynamic drag on particles is significantly enhanced close to a plane or curved boundary. This enhancement impedes the movement of the particles in both the parallel and the normal directions with respect to the wall. In the presence of a temperature gradient, the Brownian movement of particles induces the phenomenon of thermophoresis, which results in the steady motion of the particles toward the colder domains of the flow field. This paper examines the effect of the enhanced wall drag on the thermophoretic movement of the nanoparticles in a Newtonian fluid, at short distances (0–10 radii) from a flat, horizontal wall. The effect of the flow shear lift on the thermophoretic motion of the particles close to a horizontal wall is also examined. It is observed that the movement of the particles toward the plane wall is significantly retarded because of the enhanced drag and that it, actually, causes particle accumulation close to the plane wall. It is also observed that the lift, which is induced by the relative Brownian movement, does not have an effect on the average motion of particles toward the wall and does not play an important role on the deposition of particles.

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Figures

Grahic Jump Location
Fig. 1

The time-average velocity of 1000, 30 nm particles subjected to the Brownian force. The ensemble average velocity is the thermophoretic velocity, Vth.

Grahic Jump Location
Fig. 2

The retardation coefficient, due to the plane wall

Grahic Jump Location
Fig. 3

The final relative position of the two ensembles of particles after 5000τp (4.93 × 10−6 s) and after 500,000τp (4.93 × 10−4 s). All particles were released at h/α = 5.5α.

Grahic Jump Location
Fig. 4

The higher fraction of particles of the second ensemble in the wall region

Grahic Jump Location
Fig. 5

The shear lift force on a sphere close to a wall with negative relative velocity

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