The dynamics and stability of thin liquid films have fascinated scientists over many decades: the observations of regular wave patterns in film flows down a windowpane or along guttering, the patterning of dewetting droplets, and the fingering of viscous flows down a slope are all examples that are familiar in daily life. Thin film flows occur over a wide range of length scales and are central to numerous areas of engineering, geophysics, and biophysics; these include nanofluidics and microfluidics, coating flows, intensive processing, lava flows, dynamics of continental ice sheets, tear-film rupture, and surfactant replacement therapy. These flows have attracted considerable attention in the literature, which have resulted in many significant developments in experimental, analytical, and numerical research in this area. These include advances in understanding dewetting, thermocapillary- and surfactant-driven films, falling films and films flowing over structured, compliant, and rapidly rotating substrates, and evaporating films as well as those manipulated via use of electric fields to produce nanoscale patterns. These developments are reviewed in this paper and open problems and exciting research avenues in this thriving area of fluid mechanics are also highlighted.

Dynamics and stability of thin liquid films

Measurement of liquid film thickness and the determination of spin-up radius on a rotating disc using an electrical resistance technique

The use of polymer flooding as one of enhanced oil recovery methods has recently increased. The occurrence of high shear rates in reservoir and near well bore through perforation nozzles during polymer flooding cause shear degradation of polymers and therefore polymer viscosity has decreased. Rheological behavior of polymer solution in different conditions of oil reservoir is one of the key factors to develop use of polymer solutions. A few researches are available regarding improving rheological behavior of polymeric solution. In this study, to investigate the effect of nanoparticles on rheological behavior of polymer solutions two samples were prepared: polyacrylamide solution in water and suspension of silica nanoparticles in polyacrylamide solution. The sample viscosities in different shear rates were measured. The best rheology models were developed to state rheological behavior of prepared samples and the measured data were compared to power law model. An increase in the viscosity of the suspension ...

An Experimental Investigation of Silica Nanoparticles Effect on the Rheological Behavior of Polyacrylamide Solution to Enhance Heavy Oil Recovery

Experiments of single water drop impact onto a plane water surface were carried out to investigate the effect of impingement angle on the total mass of secondary drops produced during the collision. When the impingement angle (the angle between the velocity vector of primary drop and the normal vector to water surface) was less than 50°, an increase in the impingement angle led to a remarkable increase in the total mass of secondary drops; this could be attributed to a significant increase in the secondary drop size. However, no secondary drop was observed within the experimental ranges tested when the impingement angle exceeded 70°.

Effect of impingement angle on the outcome of single water drop impact onto a plane water surface

A numerical study on splash of oblique drop impact on wet walls

Steady flow of a liquid jet from a nozzle onto the centre of a rotating disk is studied with a streak line method to determine the superficial velocity of the spreading liquid film. Good agreement is found with an asymptotic analysis of the unperturbed flow field. Experimentally, the liquid surface is always perturbed by surface waves which appear as regular spirals, steady in the laboratory system in the low Reynolds number range. It could be shown that wave formation is very sensitive to entrance conditions. Therefore, it is assumed that wave generation is an entrance effect which acts as periodic forcing on the forming liquid film. Wave velocities outside the entrance region are measured and proved to be in good agreement with the prediction of a linear stability theory, as long as the flow rate and entrance perturbations are small. At higher flow rates or stronger disturbances, the radial development of the wave velocities takes on the characteristics predicted by nonlinear stability theories and is in qualitative agreement with experiments performed on an inclined plane.

Surface instabilities of thin liquid film flow on a rotating disk

Oblique impact of single drops on deep fluids at various impact angles a is studied for a wide Weber number range (15≤We≤249), where a is varied between 5.4° and 64.4° with respect to the target surface, and drop and target consist of the same fluid (water/glycerol). In the range of studied parameters, coalescence always takes place. Below a critical level of the Weber number We N formed with the normal velocity component, We N 10, a lamella is ejected from the target surface and drop volume for which both experimental and numerical evidence is given. For We 10, it occurs in the front part of the spreading drop; for a > 23°, in the rear part of the impact crater. The spreading patterns of the drop fluid are visualized with dyed drop fluid once it has come to rest after impact. In many cases, patterns of high complexity and strong sensitivity to the impact conditions can be seen which are very reproducible for similar impact conditions. The mechanisms underlying capillary wave or lamella formation and the partial immersions of drop fluid are discussed and their relevance for pattern formation is taken into account.

Regimes of drop morphology in oblique impact on deep fluids

Shear degradation and deformation of polysaccharides in thin liquid film flow on a rotating disk.

Effect of surfactants on the stability of thin liquid film flow on a rotating disk

For a semi-continuous model of the Boltzmann equation (1) peculiar solutions are obtained and generally the global existence of solutions of the initial value problem is discussed. The global existence is possible even in some cases for partially negative initial number densities, which are not physical problems, but mathematical ones. It can be shown that in some cases the entropy begins to increase, reaches a maximum and decreases again.

Karl G. Roesner

Papers

Surface instabilities of thin liquid film flow on a rotating disk

Regimes of drop morphology in oblique impact on deep fluids

Shear degradation and deformation of polysaccharides in thin liquid film flow on a rotating disk.

Effect of surfactants on the stability of thin liquid film flow on a rotating disk

Study of a new semi-continuous model of the Boltzmann equation