Optimizing Sensitivity in a Fluid-Structure Interaction-Based Microfluidic Viscometer: A Multiphysics Simulation Study

Abstract

Fluid-structure interactions (FSI) are used in a variety of sensors based on micro- and nanotechnology to detect and measure changes in pressure, flow, and viscosity of fluids. These sensors typically consist of a flexible structure that deforms in response to the fluid flow and generates an electrical, optical, or mechanical signal that can be measured. FSI-based sensors have recently been utilized in applications such as biomedical devices, environmental monitoring, and aerospace engineering, where the accurate measurement of fluid properties is critical to ensure performance and safety. In this work, multiphysics models are employed to identify and study parameters that affect the performance of an FSI-based microfluidic viscometer that measures the viscosity of Newtonian and non-Newtonian fluids using the deflection of flexible micropillars. Specifically, we studied the impact of geometric parameters such as pillar diameter and height, aspect ratio of the pillars, pillar spacing, and the distance between the pillars and the channel walls. Our study provides design guidelines to adjust the sensitivity of the viscometer toward specific applications. Overall, this highly sensitive microfluidic sensor can be integrated into complex systems and provide real-time monitoring of fluid viscosity.

Keywords: deflection; fluid-structure interaction; microfluidic viscometer; micropillar; multiphysics simulations.

Figure 1

Geometric design parameters utilized in the FSI-based microfluidic viscometer. $D$: pillar diameter, $H$: pillar height, $g$: gap between micropillar tip and channel ceiling, $d$: pillar spacing, $CW$: channel width, $CH$: channel height.

Figure 2

The impact of aspect ratio on FSI-based microfluidic viscometer sensitivity: (a–c) Micropillar displacement as a function of fluid viscosity at various flow rates for three different micropillar aspect ratios. (d) Sensitivity ($s$) of the viscometer as a function of aspect ratio. The sensitivity of the viscometer increases with aspect ratio.

Figure 3

The impact of gap ($g$) between the micropillar tip and channel ceiling on FSI-based microfluidic viscometer sensitivity. The sensitivity ($s$) of the viscometer as a function of the normalized gap ($g/H)$ for three different micropillar aspect ratios: (a) $AR=3:1$, (b) $AR=4:1$, and (c) $AR=5:1$. The sensitivity reaches a maximum at normalized gap values of $g/H=0.1667$, $g/H=0.125$, and $g/H=0.1333$ for $AR=3:1$, $AR=4:1$, and $AR=5:1$, respectively. Flow rates ($Q_1-Q_7)$ are provided in Figures S3–S5.

Figure 4

The impact of channel width ($CW$) on FSI-based microfluidic viscometer sensitivity: (a–c) The sensitivity ($s$) of the viscometer as a function of the channel width ($CW)$ for three different micropillar aspect ratios. The sensitivity increases with decreasing channel width for all aspect ratios. Flow rates ($Q_1-Q_7)$ are provided in Figures S6–S8.

Figure 5

The impact of pillar spacing ($d$) on FSI-based microfluidic viscometer sensitivity. The sensitivity ($s$) of the viscometer as a function of the pillar spacing ($d)$ for flow rates between 15 and 105 mL/h. The sensitivity moderately increases with pillar spacing.

Figure 6

The impact of Young’s modulus ($E$) on FSI-based microfluidic viscometer sensitivity. The sensitivity ($s$) of the viscometer as a function of the Young’s modulus ($E)$ for flow rates between 15 and 105 mL/h. The sensitivity decreases with Young’s modulus.