Experimental and Numerical Investigations on Micromixers and Micropumps for Performance Enhancement in Point-of-Care (POC) Applications

Buglie, Lawrence Nanu (2025) Experimental and Numerical Investigations on Micromixers and Micropumps for Performance Enhancement in Point-of-Care (POC) Applications. PhD thesis, UNIMAS.

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Abstract

Point-of-care (POC) device is a medical tool for a rapid initial diagnosis of near-patient testing which suits the necessities in telemedicine. In POC devices, lamination-based passive micromixers have been largely used. This, however, requires a long mixing channel to mix fluid or bioassays completely. To overcome this, structured two-dimensional (2D) mixing channels have been introduced as an alternative to achieve the same mixing performance but with a shorter channel length. Hence, in this present study, two variants of the obstacle-based 2D passive micromixer were shortlisted, namely the T-micromixer with circular mixing channel and Tesla micromixer were introduced and fabricated to identify the best micromixer for POC application. Micromixer selection was based on the liquid mixing performance determined using the RGB method. Tesla micromixer was selected due to the capability to mix fluid completely (MI = 100%) compared to the T-micromixer with circular mixing channel (MI =57.33%) at the same Re = 40. On the other hand, passive micropumps are alternatives for conventional benchtop pumps used in POC devices due to the latter are usually placed at the micromixer inlets hence multiple units are required to drive fluids into a micromixer that has many inlets. Apart from that, running on these conventional pumps also may cause leakage in the device due to the higher working pressure than the ambient. Therefore, to cope with these shortcomings, two variations of the passive micropump were suggested, namely the multi-angle paper-based capillary (MAPC) and sub-atmospheric pressure (SAP) micropumps. They were fabricated and assessed for the selection of the suitable micropump to be used in the proposed POC unit. The micropump selection was based on the flow rate performance of the mentioned micropumps. During standalone operations, the SAP micropump has a higher flow rate (Q = 49.9 µL/s) as compared to the MAPC micropump (24.4 µL/s), thus it was selected to be integrated with Tesla micromixer in the proposed POC unit. SAP micropumps were identified to be suitable for attachment to the outlet of a micromixer for overcoming the leakage problem in tubing networks. In the final stage, the numerical investigation was done in terms of CFD simulations to optimize the gauge pressure of the integrated unit of the Tesla micromixer and SAP micropump. Optimization showed a complete fluid mixing was achieved at a gauge pressure of -10 kPa. In addition, the simulation showed that fluid mixing was caused by the generation of Dean vortices and minor chaotic advection at each valve stage. It was also identified that the actual gauge pressure was lesser than the simulated gauge pressure, and found to be diminished with time due to the physical limitation of the micropump chamber. In overall, the mixing performance between the simulation and experiment compares well despite the deviation of about -0.51 kPa, and demonstrates the viability of the proposed POC unit for enhanced fluid mixing.

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