History of lubrication: Osborne Reynolds

Lubrication Engineering, Oct 1999

In the Science of Mechanical Engineering there is probably no name better known than that of Osborne Reynolds. His contributions cover the entire field and in such a fundamental way that his prominence seems likely to be enduring.

Reynolds was born at Belfast in 1842. His father and grandfather were clergymen in the Church of England, and from his father who took high honors in mathematics at Cambridge he inherited his own considerable talents in this subject. Reynolds graduated from Cambridge in 1867 as Seventh Wrangler. (An honors man placed in the first class in the Mathematical Tripos at Cambridge University). After a very short employment as a civil engineer he applied and was accepted for the Chair of Engineering at the Owens College, University of Manchester, where he spent the rest of his active life.

During the course of about thirty-five years, Reynolds made original and lasting contributions in meteorology, hydrodynamics, lubrication, flow of gases, marine propulsion, and in the application of dynamical similarity to tidal and river phenomena. His large-scale determination of the mechanical equivalent of heat, by using the energy dissipated in a brake on a steam engine to heat water from the temperature of melting ice to boiling, is a work of classical importance in science.

The great contributions Reynolds made in the science of lubrication was a logical extension of earlier work in hydrodynamics. In a classical paper, "An Experimental Investigation of the Circumstances Which Determine Whether the Motion of Water Shall Be Direct or Sinuous and of the Law of Resistance in Parallel Channels," he advanced the science of hydrodynamics in a fundamental way. The great divergence between the findings of Poiseuille and Darcy, the former reporting a head loss in fine bore tubes directly proportional to the velocity, and the latter reporting for pipe flow a dependence on the square of the velocity, was elucidated by this work. It is well known today that the two divergent results were obtained under flow conditions of widely different Reynolds Number, and it was in these papers by Reynolds that this well known criterion was first applied to demark these two distinctly different flow regimes.

In the reports on the friction experiments for the Institution of Mechanical Engineers subsequent to the appearance of Reynolds' famous paper, "On the Theory of Lubrication and Its Application to Mr. Beauchamp Tower's Experiments," there is no mention or acknowledgment of this great work. The omission is so noticeable as to suggest at least a lack of enthusiasm for the massive theoretical interpretation of the committee's findings. And yet, if this analysis had not been made or if such an analysis had not been possible, Tower's work would have been relegated to obscurity and the subsequent developments of Kingsbury and Mitchell might never have been made. For this reason, and in spite of Tower's precedence, it seems altogether fair to consider Osborne Reynolds the founder of the science of lubrication.

In his great paper Reynolds solved the problem of the inclined plane slider neglecting the side leakage, but unaccountably missed its implication in the troublesome thrustbearing problem on shipboard. This is the more remarkable in view of his extensive work on ship propulsion. His only subsequent reference to lubrication in his published work is contained in a short paper. "On the Slipperiness of Ice." In working with a soldering iron he observed that the hot iron moved along with surface of a piece of solder with virtually no resistance. The similarity of the action to that of a skate on ice immediately occurred to him. The explanation of the easy motion of a skate being a lubrication phenomenon was given in this paper apparently for the first time. The lowering of the freezing point of water by the action of pressure had previously been pointed out by James Thomson, elder brother of Lord Kelvin. Reynolds, from this, deduced the existence of a water film between skate and ice due to the high contact pressure, and the analogy to the soldering iron incident was complete.

Reynolds' contributions to science and engineering are contained in three volumes of his collected papers. They contain a surprising number of scientific developments that are today the working equipment of engineers and physicists as well as rational explanations of many natural phenomena. In the latter category are such things as the explanation of why timbers in buildings hit by lighting are burst asunder. Reynolds attributed it to the sudden evaporation of the moisture present in the wood by the passage of the electricity. The production of steam is sufficiently rapid to amount to an explosion throughout the wood thus bursting it. The explanation of the quieting effect of oil on rough water, as due to eddies caused by relative motion between the contiguous surfaces of oil and water thus dissipating the energy going into wave making, was an outgrowth of his studies on fluid motion. The somewhat similar quieting effect rain has on rough water was also explained by Reynolds as due to each rain drop carrying down into a wave a certain amount of water from the surface. Since the various layers of water in a wave have different velocities, a momentum transfer is effected by the progress of the rain drops. This results in energy dissipation and the violent surface motion is reduced.