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A Dynamic Model of Drag Force for Catalytic Micromotors Based on Navier⁻Stokes Equations

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A Dynamic Model of Drag Force for Catalytic Micromotors Based on Navier⁻Stokes Equations

Zhen Wang et al. Micromachines (Basel).

Abstract

In past decades, considerable advances have been achieved in micro and nanomotors. Particular attention has been given to self-propelled catalytic micromotors, which have been widely used in cell separation, drug delivery, microsurgery, lithography and environmental remediation. Fast moving, long life micromotors appear regularly, however it seems there are no solutions yet that thoroughly clarify the hydrodynamic behavior of catalytic micromotors moving in fluid. Dynamic behavior of this kind of micromotors is mainly determined by the driving force and drag force acting on the micromotors. Based on the hydromechanics theory, a hydrodynamic model is established to predict the drag force for a conical micromotor immersed in the flow field. By using the computational fluid dynamics software Fluent 18.0 (ANSYS), the drag force and the drag coefficient of different conical micromotors are calculated. A mathematical model was proposed to describe the relationship among Reynolds numbers Re, the ratio λ, the semi-cone angle δ and the drag coefficient Cd of the micromotors. This work provides theoretical support and reference for optimizing the design and development of conical micromotors.

Keywords: Navier-Stokes equation; conical micromotor; drag force; hydromechanics.

Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Schematic and SEM image of the micromotor.
Figure 2
Figure 2
Numerical model and boundaries for simulating the drag force.
Figure 3
Figure 3
Results calculated by Fluent numerical calculation software. The length of the micromotor is 10 μm. The semi-cone angle is 5°, the larger radius is 5 μm and the inlet velocity of the fluid is 5 mm/s. (a) The pressure distribution on the surface of the micromotor; (b) the velocity distribution of the flow field around the micromotor.
Figure 4
Figure 4
The drag force (a) and drag coefficient (b) versus the Reynolds number ranging from 4 × 10−4 to 2 × 10−2.
Figure 5
Figure 5
The drag force and drag coefficient versus semi-cone angle ranging from 1° to 7°.
Figure 6
Figure 6
The drag force and drag coefficient versus the rate of length to larger radius ranging from 4 to 7.
Figure 7
Figure 7
The numerical fitting results of the drag coefficient Cd versus (a) Re, (b) δ and (c) λ.

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