Experimental Study on Formation of Particle Accumulation Structures by a Thermocapillary Flow in a Deformable Liquid Column

Abstract

A series of experiments has been performed under earth's gravity to study formation of particle accumulation structures (PAS) in a supercritical flow driven by the combined effects of buoyancy and thermocapillary forces. The test flow was created in a non-isothermal cylindrical column (liquid bridge) made of n-decane and heated from above. The objective of the experiment was to answer two major questions: (1) how strong is the influence of the shape of the interface on the process of formation of PAS;(2) what temperature of the ambient air fits better for PAS to occur. Considering these questions, we developed a method based on changing both the volume of the liquid bridge and temperature at the external walls of the experimental chamber to set and to keep constant the shape of the interface and the temperature inside the setup, respectively. The experimental observations are presented in the form of diagrams in the parameters' space showing ranges of the PAS formation. The findings show that a liquid bridge with an interface as close to the straight cylindrical as possible and surrounded by air at low temperature is the best terrain for D. Melnikov ( ) · V. Shevtsova Université Libre de Bruxelles (ULB), MRC, CP-165/62, PAS formation. The results of the chaos analysis of the recorded temperature time series and their correlation with the obtained diagrams allow for showing that accumulation of particles in coherent structures is possible only in a periodic oscillatory flow characterized by a small value of the translation error not exceeding 0.01. It is demonstrated that presence of either any spectral noise or of several modes with incommensurate frequencies makes formation of a PAS impossible.

Symmetry breaking phenomena in thermovibrationally driven particle accumulation structures

“…Love and Pettit 23 and by Tabakova and Zapruanov 24 , Wunenburger et al, 25 , Thomas and Gollub 26 , Ivanova et al, 27 , Kozlov et al, 28 . This realization has led over the years to the establishment of an independent, elegant theoretical framework that is nowadays known as the "study of inertial particle in time-periodic flows" 2-3, [29][30][31][32][33][34][35][36][37][38] .…”

Particle accumulation structures in noncylindrical liquid bridges under microgravity conditions

“…To the best of our knowledge the experimental studies by [44] and [8] are the only works in which the effect of interface deformation on PAS formation was investigated (though under normal gravity conditions). Here the problem is addressed numerically with the two-fold intention to 1) study situations (microgravity) for which no experimental data are avail-able and 2) provide additional details and insights into the topological and morphological evolution of PAS when non-straight interfaces are considered.…”

“…Though this numerical approach should clearly be regarded as a simplification of reality (obviously this scheme cannot describe particle interaction when accumulation takes place), it has enjoyed a widespread use in the literature for the study of PAS ([3-5], [10], [29], [34][35][36], [43], [48]) . A justification or rationale for such a practice can be found in available experimental observations or data ( [2], [6][7][8][9], [19], [37][38][39][40][41], [44]). Indeed, experiments dealing with a variety of fluids and particle types have shown that once particles enter the attractor (the KAM torus), they can no longer leave it (inter-particle forces are not sufficiently strong to allow particles to get away from the attractor).…”

“…for increasing values of the volume ratio, as witnessed by the curves, the linear extension of the structure shows no obvious sign to reach a limit (as one would expect on the basis of geometrical considerations similar to those elaborated above for the case of very slender liquid bridges). A simple way to think Notably, the same quantity was also used for the characterization of experimentally-obtained PAS by [44]. The values taken by this parameter (evaluated as This time, the key to understanding the results lies in considering that, if the diameter of the supporting rods is kept fixed, a decrease in the height of the liquid column (i.e.…”

“…A similar concept also applies to the influence of the volume of liquid effectively held between the two disks supporting the liquid bridge for a fixed geometrical aspect ratio. However, only a few experiments have appeared in the literature dealing with this aspect [8,44]. Unfortunately, numerical results are completely absent due to the difficulties typically associated with the numerical simulation of non-cylindrical geometries.…”