The traditional boundary condition in fluid mechanics, known as the no-slip boundary condition, assumes that a fluid adjacent to a solid surface experiences no relative motion. However, this assumption has been challenged by experimental and numerical studies, particularly in the field of microfluidics. These studies have observed a relative motion between the wall and the adjacent fluid, characterized by a slip velocity, us. When the velocity profile of the fluid is extrapolated from the wall-fluid interface toward the wall, it reaches the wall velocity. The distance from the wall at which this occurs is called the slip length, λ. This slip length can be used to modify the no-slip condition, providing a more accurate representation of fluid behaviour in certain situations.
For Newtonian fluids, the slip lengths are typically on the order of hundreds of nanometres. In narrow gaps, such as those in hydraulic seals and journal bearings, the partial slip boundary condition, where slip is allowed at the wall, can significantly impact fluid dynamics calculations.
The primary objective of this research is to experimentally investigate the slip length using a Slip Length Tribometer (SLT) across a range of lubricants and technical surfaces. The study seeks to identify the key factors influencing wall slip, including temperature, surface roughness, the molecular structure of lubricants, the lattice arrangement of solid surfaces, and lubricant additives. These factors are expected to play a crucial role in determining slip length and, consequently, the performance of lubrication systems.
