Squeeze fluid film of spherical hydrophobic surfaces with wall slip

Performance of hydrodynamic lubrication journal bearing with a slippage surface

“…The slip length employed in their numerical work is on the order of 1 mm. In such a large slip length, the slip usually exhibits a strongly non-linear behavior (Craig et al, 2000;Zhu and Granick, 2001;Bonaccurso et al, 2002;Granick et al, 2003), and one cannot use the constant slip length model to describe the slip (Wu et al, 2006b). The sleeve surface can be designed as either multilevel slip surfaces or a surface with continuously changing shear strength.…”

“…At a small range of shear rate, the slip length was found nearly a constant (Pit et al, 2000;Baudry and Charlaix, 2001;Cottin-Bizonne et al, 2005). At high shear rate, however, some experimental observations (Craig et al, 2000;Zhu and Granick, 2001;Granick et al, 2003) and MD study (Thompson and Troian, 1997) showed that wall slip is strongly nonlinear slip and can be described by the limiting shear stress model (Wu et al, 2006b).…”

“…However, they met an instability problem in numerical solution (Salant and Fortier, 2004) when the critical shear stress is nonzero, and thus concluded that the bearing operated in unstable condition in some range of sliding speed. Wu et al (2006b) found that an optimized slip zone exists for an infinite length slider bearing, giving a highest load support and smallest friction coefficient when the gap is roughly parallel. Even a slightly divergent wedge still gives a considerable large hydrodynamic support force.…”

“…It is generally accepted that an ultrahydrophobic surface gives a larger wall slip, but a hydrophilic surface gives no slip or a very small slip (Craig et al, 2000;Pit et al, 2000;Baudry and Charlaix, 2001;Spikes, 2003a;Granick et al, 2003;Cottin-Bizonne et al, 2005). The surface limiting shear stress for a slip to occur was found as low as 0.33 Pa for an interface of deionized water and atomically smooth surfaces of micas coated with a methyl-terminated close-packed monolayer of condensed octadecyltriethoxysiloxane (Granick et al, 2003;Wu et al, 2006b). Wall slip has received much attention in various fluid flows, including polymer flow (Barnes, 1995), gas gap flow in MEMS (micro-electromechanical system) (Lee et al, 2005), Stokes and Couette flows (Khaled and Vafai, 2004), and fluid gap flow in hydrodynamic lubrication systems (Spikes, 2003a,b;Wu and Ma, 2005).…”

“…So far two main slip models have been used to describe the boundary slip: 1 Constant slip model (Navier, 1823;Vinogradova, 1995). 2 The limiting shear stress model (Wu et al, 1992;Spikes, 2003a,b;Wu and Ma, 2005;Wu et al, 2006b;Wu and Sun, 2006) based on the work of Winer (1979, 1992). In the slip length model, the slip velocity, u s , is assumed to be proportional to local shear rate ›u=›z, i.e.…”