Threshold onset of Marangoni convection in narrow channels
1 Institute of Continuous Media Mechanics, UB Russian Academy of Sciences Acad. Koroleva 1, 614013 Perm, Russia
2 Seconda Universita di Napoli, Dipartimento di Ingegneria Aerospaziale Meccanica, via Roma 29, 81031 Aversa, Italy
a e-mail: email@example.com
Revised: 25 January 2011
Published online: 9 March 2011
There are several experimental studies where the Marangoni convection begins only at a certain difference in the surface tension, i.e. in a threshold way. This effect contradicts a traditional point of view according to which the surface flow in Newtonian fluids should begin at an arbitrary small difference in surface tension. To explore this phenomenon in detail we investigated the initiation of the Marangoni convection at a free liquid surface caused by injection of a droplet of surfactant. It was found that the surface motion occurs in a threshold manner, i.e. when a surfactant concentration in the droplet approaches a certain critical value. The described phenomenon is more important in narrow channels and essentially depends both on the purity of the basic liquid and on the surfactant used. Based on the experimental results, a hypothesis about an important role of residual impurities contained in basic liquids which can thoroughly change a surface rheology was suggested. The theoretical model taking into account special rheological properties in the free surface is considered. The results of the numerical simulation are in a good agreement with the experimental observations.
© EDP Sciences, Springer-Verlag, 2011