Abstract
Having a basic understanding of non-Newtonian fluid flow through porous media, which usually consist of series of expansions and contractions, is of importance for enhanced oil recovery, groundwater remediation, microfluidic particle manipulation, etc. The flow in contraction and/or expansion microchannel is unbounded in the primary direction and has been widely studied before. In contrast, there has been very little work on the understanding of such flow in an expansion–contraction microchannel with a confined cavity. We investigate the flow of five types of non-Newtonian fluids with distinct rheological properties and water through a planar single-cavity microchannel. All fluids are tested in a similarly wide range of flow rates, from which the observed flow regimes and vortex development are summarized in the same dimensionless parameter spaces for a unified understanding of the effects of fluid inertia, shear thinning, and elasticity as well as confinement. Our results indicate that fluid inertia is responsible for developing vortices in the expansion flow, which is trivially affected by the confinement. Fluid shear thinning causes flow separations on the contraction walls, and the interplay between the effects of shear thinning and inertia is dictated by the confinement. Fluid elasticity introduces instability and asymmetry to the contraction flow of polymers with long chains while suppressing the fluid inertia-induced expansion flow vortices. However, the formation and fluctuation of such elasto-inertial fluid vortices exhibit strong digressions from the unconfined flow pattern in a contraction–expansion microchannel of similar dimensions.
Highlights
As the earth’s conventional oil and gas resources are steadily running out, effective processes such as hydraulic fracturing to enhance the productivity of unconventional reservoirs are attracting interest lately [1]
We have experimentally studied the flow of five types of non-Newtonian polymer solutions and compared them with that of water in a planar expansion–contraction microchannel
The tests were performed with a wide range of Reynolds and Weissenberg numbers, from which the sole and combined effects of fluid inertia, shear thinning, and elasticity are demonstrated under the confined condition in the cavity
Summary
As the earth’s conventional oil and gas resources are steadily running out, effective processes such as hydraulic fracturing to enhance the productivity of unconventional reservoirs are attracting interest lately [1]. The flow patterns of various polymer solutions such as polyethylene oxide (PEO) [46,47,48,49,50], polyacrylamide (PAA) [51,52,53], polyvinylpyrrolidone (PVP) [35], XG [35,54], DNA [55,56], and surfactant [57,58] solutions have been investigated in contraction and/or expansion microchannels to recognize both the sole and combined effects of fluid rheological properties (namely elasticity and shear thinning [59]) and inertia. It is important to note that our tested fluids have been commonly used in microfluidic applications [13,16,17,18,70], rendering them useful to be studied directly These fluids possess different elastic and shear thinning properties, though their infinite-shearrate viscosity values are comparable. The observed flow patterns are compared with those of the same fluids through a planar contraction–expansion microchannel of similar dimensions [35] for a further understanding of the confinement effect
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