Abstract
This paper presents an approach for the measurement of a liquid film thickness in contact with a rough surface, based on electrical conductance sensor. This type of sensor consists of two electrodes mounted flush on a wall and using an electrolyte solution representing the liquid film. Assessing of the generated current between a pair of electrode is used as a measure of the film thickness. The liquid film is contained between two parallel surfaces that one of which is coated with a certain roughness, while the other is smooth. The electrical probes are placed on the smooth surface and the facing rough surface is removable allowing a free move of the wall. In this way, a rotational or a sliding motion is imposed on the rough wall allowing a browse of an entire surface relative to the electrode, in order to determine the influence of roughness on the film thickness measurements. In addition, series of signal acquisition were carried out with imposed pressures on the upper plate for the characterization of the effect of the film compression on the measured thicknesses. The principle of this electrochemical technique is briefly explained, as well as how the lateral distance between the electrodes impacts the measuring range limit. The experimental setup is described and used to study the liquid film flow with several configurations of the wall surface. The obtained results demonstrated the feasibility of this type of non-intrusive estimation, as it was possible to estimate the variable film thickness which is depending on the peaks and valleys of the rough surface. This is promising, because measuring this parameter remains difficult. Finally, the results analysis allows to synthesize the advantages and limitations of this method.
Highlights
We focused our attention in this study on the effects of a rough surface on the film thickness timevariation
The results show that this method can be accurately used to measure the thickness of a liquid film and can precisely detect the various irregularities created by such rough surfaces
The upper surface, facing the probes, was coated with a given roughness, in order to check the influence of this wall aspect on the liquid film thickness
Summary
Liquid films wetting surfaces (stationary or mobile) can play a key role; as a heat transfer vector, such as in the packing on the distillation towers or on fuel rods of boiling water reactors, were the liquid film presents a necessary condition to provide a favorable environment. In almost all mechanical applications, the liquid film can be involved as a lubricant to avoid or to reduce problems and drawbacks, such as the friction and the wear in the sliding bearings in which the surfaces are in contact in a relative motion. At this point, the interest of the measurement of the lubrication film thickness arises as a quantitative way for reducing the tribological problems and so, the optimization of industrial process. During the lubrication regime, unlike smooth surface when surfaces are irregulars, pressure and surface roughness may influence on the liquid film thickness between the two working surfaces. The knowledge of the irregularities effects on the liquid film thickness plays an important role for the inspection and the control of the lubricating systems on a given mechanism
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