Simulations of slip flow on nanobubble-laden surfaces

Abstract

Abstract. On microstructured hydrophobic surfaces, geometrical patterns may lead to the appearance of a superhydrophobic state, where gas bubbles at the surface can have a strong impact on the fluid flow along such surfaces. In particular, they can strongly influence a detected slip at the surface. We present two-phase lattice Boltzmann simulations of a flow over structured surfaces with attached gas bubbles and demonstrate how the detected slip depends on the pattern geometry, the bulk pressure, or the shear rate. Since a large slip leads to reduced friction, our results allow to assist in the optimization of microchannel flows for large throughput.

Control of slippage with tunable bubble mattresses

“…The overall average velocity in this case is still higher than that for nonslippery walls. These observations are consistent with the numerical findings of Hyväluoma et al (13). Fig.…”

“…Our simulations reveal an asymmetry in the effective slip length between positive and negative protrusion angles, affirming previous reports (13,14,(18)(19)(20). Consistent with the experimental results, the numerical b eff increases with increasing protrusion angle to a maximum value at θ = 11°and subsequently decreases with further increases in θ for all φ.…”

“…The effective slip length becomes zero at a critical protrusion angle, θ c , above which the microbubbles exhibit negative slip length, revealing a transition from slippage to extra friction. Our simulations yield θ c ≈ 628 and θ c ≈ 688 for φ = 0.54 and φ = 0.38, respectively, which are quantitatively consistent with the results of previous theoretical and numerical studies (13,14,(18)(19)(20).…”

“…In particular, microscale bubbles transverse to the flow direction can alter the flow resistance, depending on the protrusion of the bubbles into the flow. Moreover, transition from slippage to friction has been predicted for trapped bubbles perpendicular to the flow in theoretical (14, 18) and numerical studies (12,13,19,20). The presence of such a critical protrusion angle highlights the feasibility of manipulating the flow resistance via bubble geometry.…”

“…Hydrophobic microstructures containing trapped gas bubbles have been shown to be advantageous for drag reduction (5)(6)(7)(8)(9)(10)(11). Their orientation with respect to the flow direction (12)(13)(14)(15)(16) and the geometry of gas-liquid menisci (11)(12)(13)(14)17) has been demonstrated to affect the slippage. In particular, microscale bubbles transverse to the flow direction can alter the flow resistance, depending on the protrusion of the bubbles into the flow.…”