J. Meseguer

A Review on the Stability of Liquid Bridges

Abstract Errors in the Although early studies dealing with the stability of liquid bridges were published long time ago, these studies were mainly concerned with the stability of axisymmetric liquid bridges between parallel, coaxial, equal-in-diameter solid disks, with regard to axisymmetric perturbations. Results including effects such as solid rotation of the liquid column, supporting disks of different diameters and an axial acceleration acting parallel to the liquid column can be found in several works published in the early eighties, although most of these analysis were restricted to liquid bridge configurations having a volume of liquid equal or close enough to that of a cylinder of the same radius. Leaving apart some asymptotic studies, the analysis of non-axisymmetric effects on the stability of liquid bridges (lateral acceleration, eccentricity of the supporting disks) and other not so-classical effects (electric field) has been initiated much more recently, the results concerning these aspect of liquid bridge stability being yet scarce.

Wind tunnel study on the influence of different parapets on the roof pressure distribution of low-rise buildings

Abstract High suction loads appear on roofs of low-height buildings. The use of parapets with appropriate height at the roof edges alleviates these loads. The performance of six parapet configurations to decrease the suction loads induced on roofs by oblique winds has been studied in a low speed wind tunnel. The studied parapet configurations include vertical wall parapets, either solid or porous, and cantilevered parapets formed by a small horizontal roof close to the building roof. Low-height parapets with a medium porosity and cantilevered parapets are more efficient than solid parapets to reduce the wind suctions generated on the roofs by conical vortices.

On the breaking of long, axisymmetric liquid bridges between unequal supporting disks at minimum volume stability limit

Abstract The stability of axisymmetric liquid bridges held between non-equal circular supporting disks, and subjected to an axial acceleration, has been analyzed both theoretically and experimentally. Some characteristics of the breaking process which takes place when the stability limit of minimum volume is reached (mainly the dependence with the disks separation of the volume of the liquid drops resulting after the liquid bridge breakage) have been theoretically studied by using standard asymptotic expansion techniques. From the analysis of the nature of the unstable equilibrium shapes of minimum volume at the stability limit it is concluded that the relative volume of the main drops resulting from the liquid bridge rupture drastically change as the disks separation grows. Theoretical predictions have been experimentally checked by working with very small size liquid bridges (supporting disks being some 1xa0millimeter in diameter), the agreement between theoretical predictions and experimental results being remarkable.

A small platform for astrophysical research based on the UPM-Sat 1 satellite of the Universidad Politécnica de Madrid

UPM-Sat 1 is a small scientific, in-orbit demonstration, educational satellite which has been designed, built, tested, integrated, launched and operated by a team of professors, students, and auxiliary personnel belonging to the Universidad Politecnica de Madrid (UPM). After completion of UPM-Sat 1 Mission a new small satellite, UPM-Sat 2, oriented to low-Earth-orbit scientific mission has been designed. In this paper the different subsystems of UPM-Sat 1 are described and the main characteristics of the second small satellite UPM-Sat 2 are outlined.

SIMULATION OF NON-AXISYMMETRIC FLOATING ZONE CRYSTAL GROWTH UNDER MICROGRAVITY

The possibility of growing crystals of non-circular cross-section by using the floating zone technique is considered, basing the analysis on the isothermal liquid bridge model, and restricting the study to a linear asymptotic analysis.An almost square initial seed is considered in more detail, although the analysis is general and can be applied to other initial shapes, not only of the seed but also of the supply rod, that can be of any cross-section.The influence of non-circular seed and/or feed cross-section shape, and of a possible axial acceleration typical of microgravity platforms (sounding rockets and space labs), on both the liquid interface shape and the solid grown shape, are analysed, including the stability limits by breaking of the molten bridge.

ANALYTICAL MODELLING OF FLOATING ZONE CRYSTAL GROWTH

An analytical model for predicting the outer shape evolution of a crystal grown by the floating zone technique is developed. The analysis is axisymmetric and linear in the departure from a cylindrical evolution, thus it only applies to crystal growth under negligible external force fields (e.g. under microgravity), when the seed and feed sizes do not differ too much, and when radial deformations are not pronounced. In spite of these limitations, the analytical model clearly shows that, depending on the slenderness of the molten bridge, the processing may give rise to steady growth (after some transients) or just to a breakage by capillary forces.

On the influence of marangoni convection on the stability of liquid bridge interfaces

Abstract This paper analyses the influence of the Marangoni flow on the stability of almost cylindrical liquid bridges by using bifurcation techniques. An analytical relation between the different parameters is found that allows the prediction of the variation of the maximum stable length. This variation although is qualitatively “larger” than that due to symmetric effects (f.i. volume variation, solid body rotation), can somehow be compensated with the other effects. By choosing adequately f.i. the disk diameter difference, the shortening in stability due to Marangoni convection can be almost completely cancelled.

IDR/UPM Facilities for Liquid Bridge Experimentation on Earth under Microgravity Conditions

Besides space laboratories for in-orbit experimentation, Earth based facilities for laboratory experimentation are of paramount importance for the enhancement on liquid bridge knowledge. In spite of the constraints imposed by simulated microgravity (which force to work either with very small size liquid bridges or by using the Plateau tank technique, amongst other techniques), the availability and accessibility of Earth facilities can circumvent in many cases the drawbacks associated with simulated microgravity conditions. To support theoretical and in orbit experimental studies on liquid bridges under reduced gravity conditions, several ground facilities were developed at IDR. In the following these ground facilities are briefly described, and main results obtained by using them are cited.