Effects of viscous heating and wall-fluid interaction energy on rate-dependent slip behavior of simple fluids

Abstract

Molecular dynamics simulations are used to investigate the rate and temperature dependence of the slip length in thin liquid films confined by smooth, thermal substrates. In our setup, the heat generated in a force-driven flow is removed by the thermostat applied on several wall layers away from liquid-solid interfaces. We found that for both high and low wall-fluid interaction (WFI) energies, the temperature of the fluid phase rises significantly as the shear rate increases. Surprisingly, with increasing shear rate, the slip length approaches a constant value from above for high WFI energies and from below for low WFI energies. The two distinct trends of the rate-dependent slip length are rationalized by examining S(G_{1}), the height of the main peak of the in-plane structure factor of the first fluid layer (FFL) together with D_{WF}, which is the average distance between the wall and FFL. The results of numerical simulations demonstrate that reduced values of the structure factor, S(G_{1}), correlate with the enhanced slip, while smaller distances D_{WF} indicate that fluid atoms penetrate deeper into the surface potential leading to larger friction and smaller slip. Interestingly, at the lowest WFI energy, the combined effect of the increase of S(G_{1}) and decrease of D_{WF} with increasing shear rate results in a dramatic reduction of the slip length.

The local slip length and flow fields over nanostructured superhydrophobic surfaces

“…The smaller strength of ε up WL or ε down WL is able to cause intrinsic slip at the fluid-wall interface. According to the previous works, the intrinsic slip length of order 10 σ ( Priezjev and Troian, 2004;Priezjev, 2007;Bao et al, 2017;Hu et al, 2018 ) is comparable to the local slip length at the GLI. In our work, we focus on the situation where the no-slip boundary condition is valid on the fluid-wall interface, and leave the influence of intrinsic slip on the local slip at GLI in the future work.…”

“…It is well known that for flows over a homogeneous solid surface, the velocity profiles are simply linear and parabolic for Couette and Poiseuille flows, respectively. Correspondingly, the local shear rate can be obtained by fitting the velocity profile in the bulk region and then extrapolating the fitting curve with respect to the solid-liquid interface ( Lichter et al, 2004;Priezjev and Troian, 20 04;Priezjev, 20 07;Liu and Li, 2010;Bao et al, 2017 ). However, for a liquid flowing over SHS, the presence of GLI perturbs the flow field, which leads to spatially varying velocity profiles near the GLI ( Schnecker et al, 2014 ).…”

“…Helmholtz related the magnitude of slip length to be on the order of the mean free path. During the past decades, a number of experimental ( Vinogradova, 1999;Bonaccurso et al, 2002;Granick et al, 20 03;Leger, 20 03;Spikes and Granick, 2003;Vinogradova and Yakubov, 2006;Ho et al, 2011;Vinogradova and Belyaev, 2011 ) and simulation studies ( Thompson and Troian, 1997;Barrat and Bocquet, 1999;Lichter et al, 20 04;Priezjev and Troian, 20 04;Priezjev, 2007;Huang et al, 2008;Liu and Li, 2010;Bao et al, 2017;Hu et al, 2017 ) have demonstrated that the slip length can be on the order of tens nanometers for liquids flowing over smooth nonwetting surfaces, and the μm scale slip lengths cannot be achieved without gas or air trapped at the surface.…”

Numerical Solution of Non-Newtonian Fluid Flow Due to Rotatory Rigid Disk

“…Their values are obtained by build in command in Mathematica while we have used self-coded algorithm (shooting method with R-K scheme) subject to Casson nanofluid flow induced by solid rotating disk. Beside this one can extend idea to computational fluid dynamics in context of industrial and standpoints, see References [32][33][34][35][36][37][38][39][40][41][42].…”

Effective Boundary Slip Induced by Surface Roughness and Their Coupled Effect on Convective Heat Transfer of Liquid Flow

“…The mechanisms of boundary slip are of interest, but there is still no clear understanding of the slip. Previous studies found that surface wettability is a possible reason to affect slip, however, the effect of wettability on slip can be complex and both hydrophobic and hydrophilic surface can induce either slip or no-slip boundary condition, which is dependent on the strength of solid-liquid interface [ 14 , 15 , 16 , 17 , 18 ]. Additionally, surface roughness including texture spacing and texture height can also significantly affect the degree of slip [ 18 , 19 , 20 ].…”