Experimental investigation on the drag reduction mechanism of non-Newtonian flow in microchannels with wall cavities

The research in the drag reduction mechanism of microscale flows plays a crucial role in fields such as biomedicine, energy systems, and microscale mechatronics. While most existing research primarily focuses on numerical simulations or measurements of simple Newtonian fluids flow in microchannels, little attention has been paid on non-Newtonian flow and its coupling effect with different wall cavities. In this work, we conducted a systematical investigation on the flow characteristics of non-Newtonian flow at microscale targeting on the coupling effect of the non-Newtonian shear thinning effect and cavitation structures for flow resistance reduction, where both the flow characteristics and the detailed flow fields were measured by means of self-built high speed micro-particle image velocimetry. The results prove that the coupling effect between microscale wall cavities and the shear-thinning effect of non-Newtonian flow can significantly reduce shear stress, achieving a maximum drag reduction rate of 77.06%. Among the six cavity structures tested, right-angled triangular cavities and semi-circular cavities exhibit superior drag reduction performance. The stagnant flow formed within right-angled triangular cavities can reduce the contact area between the main flow and the walls, thereby minimizing viscous losses. The highest streamlining degree of semi-circular cavities lowers localized vorticity and shear stress to reduce flow resistance. This work explores the drag reduction mechanism of non-Newtonian fluid coupled with wall cavities in microchannels from the perspective of experimental measurements, which can guide the design of microchannels focused on enhancing drag reduction and energy conservation.