(K-420) Optimal Viscosities of Sawtooth Wave Textures on a μTesla Pump

Inspired by the Tesla turbine, we previously demonstrated a microfluidic pump fabricated using consumer- grade 3D printers with surface texture enhanced pumping. In this study, we further investigate how surface texture, specifically directionality, affects the interaction between rotor surface and fluids at various viscosities, further clarifying how the the enhancement works via slip and contact length. We achieved this by modifying repeated surface textures with a sawtooth shape pointing inward or outwards with respect to the center of the rotor. Then, these pumps were assembled to drive glycerol and Xanthum solutions at various viscosities. The pumps were subjected to operational speeds of up to 4000 (rpm) to assess the hydrostatic pressure under no external loads.

As with previous μTesla pumps, the rotors, housing, and reservoirs were designed in CAD and printed with resin using an LCD-based stereolithography printer. Magnets were placed on opposite sides of the rotors before being inserted into the housing and aligned with the reservoir cap. A magnetic stir plate and simple tubing attached to a ruler were used to test and quantify the hydrostatic pressure. Water and glycerol solutions of various viscosities were used as fluid while measuring triplicates of the 2 sawtooth wave rotor designs.

Figure 1 illustrates the investigation of the effects of SAW IN and SAW OUT textures at various viscosities. It was observed that, for both textures, the maximum pressure increased with increasing viscosity until reaching a peak of 5 cP, after which it started to decline. Notably, the SAW IN texture yielded higher pressure outputs compared to the SAW OUT texture. Furthermore, when comparing the resultant pressures of the xanthum solution, Figures 1C and 1D demonstrated that the maximum pressure for the IN texture was lower than that of the 5 cP solution, whereas the opposite was true for the OUT texture.  

In our previous research, we demonstrated the optimization of μTesla textures tailored for specific viscosities. In this current abstract, we expected the enhancement to be dependent on the directionality of these textures. Counter to our initial expectation, the inward-pointing sawtooth texture generates significantly higher pressure compared to the outward-pointing texture. This disparity in pressure can be attributed to the longer contact length between the fluid and the inward-pointing sawtooth texture compared to that of the outward sawtooth, perhaps due to local vortices. This illustrates that we indeed were modifying the slip conditions through surface textures, which are not large enough to perturb between the boundary layers unlike bladed pumps.

By optimizing the micro pump via texture and directionality, we can integrate a flow source into our islet-on-a-chip system to pump microfluidic velocities without higher rotational speeds (rpms). This advancement in technology holds considerable promise for our future experiments, particularly those involving the study of shear-sensitive cells within the islet microenvironment.

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