Apparent slip of shear thinning fluid in a microchannel with a superhydrophobic wall

Abstract

The peculiarities of simple shear flow of shear thinning fluids over a superhydrophobic wall consisting of a set of parallel gas-filled grooves and solid stripes (domains with slip and stick boundary conditions) are studied numerically. The Carreau-Yasuda model is used to provide further insight into the problem of the slip behavior of non-Newtonian fluids having a decreasing viscosity with a shear rate increase. This feature is demonstrated to cause a nonlinear velocity profile leading to the apparent slip. The corresponding transverse and longitudinal apparent slip lengths of a striped texture are found to be noticeably larger than the respective effective slip lengths of Newtonian liquids in microchannels of various thicknesses and surface fractions of the slip domains. The viscosity distribution of the shear thinning fluid over the superhydrophobic wall is carefully investigated to describe the mechanism of the apparent slip. Nonmonotonic behavior of the apparent slip length as a function of the applied shear rate is revealed. This important property of shear thinning fluids is considered to be sensitive to the steepness of the viscosity flow curve, thus providing a way to decrease considerably the flow resistance in microchannels.

Hydrodynamic drag reduction of shear-thinning liquids in superhydrophobic textured microchannels

“…As can be seen in previous sections, the friction factor ratio was noticed to be minimized for the shear-thinning liquids at certain shear rates. Some of the previous research also reported that the hydrodynamic drag minimises on the SH textures when shear-thinning liquids are employed (Haase et al 2017;Patlazhan and Vagner 2017;Crowdy 2017). It is well-accepted that the reduction in hydrodynamic friction for a flow of shear-thinning liquid is attributed to the depletion layer near the wall having considerably less viscosity than the bulk liquid as shown in Fig.…”

“…16a. Consequently, Patlazhan and Vagner (2017) showed that the ratio Fig. 11 The shear rate (top panel) and viscosity (bottom panel) distribution on the bottom wall at different Carreau numbers for a flow past single post in a microchannel with HL = 0.5.…”

“…However, determination of the thickness of the depletion layer is essential to establish the non-monotonic variation of the η. ratio, which is not addressed earlier. In addition, it is also noted in the previous work that such non-monotonic variation in η. ratio is not apparent in flow over high gas fraction SH-textured surfaces due to the shear rate disturbances present in the microchannels (Patlazhan and Vagner 2017). Therefore, here we analysed the behaviour of the depletion layer to understand the non-monotonic variation in the hydrodynamic friction curves.…”

“…Micro-particle image velocimetry-based measurements confirmed their numerical results. In another research involving numerical simulations, Patlazhan et al (Patlazhan and Vagner 2017) studied a shear flow of shear-thinning liquids over ribs arranged parallel and perpendicular to the flow direction. They showed that the apparent slip length associated with shear-thinning liquids is considerably larger than those with Newtonian liquids.…”

Pressure Drop of Microchannel Plate Fin Heat Sinks

“…The slip length can be interpreted as the distance from the wall that the slip velocity profile extends to if extrapolated away from the boundary. In gas flows, the slip length is related to the Knudsen number, while in liquid flows, the slip length depends on the surface microstructure [27,28,29,30,31,32,33,34,35,36,37]. When considering liquids, the molecular mean free path may be replaced by the slip length and the Knudsen number may be replaced by the modified Knudsen number.…”