A liquid bridge stretching technique for measuring the deformation of emulsion drops in pure uniaxial extensional flow is presented. The experiments are carried out in the droptower facility of ZARM at the University of Bremen which provides microgravity conditions of about 10 ±6 g for 4.7 s.The liquid bridge is generated under microgravity and held between two plates by surface tension. The initial length and diameter of the cylindrical bridge are 30 mm. The fluid bridge is stretched exponentially to a maximum length of one meter providing a maximum Hencky strain of about 3.5. At the same time, the disk diameter is reduced exponentially from 30 to 10 mm in order to preserve the cylindrical bridge contour.The new device makes drop deformation experiments possible with emulsion drops of any density and wide-spread viscosity ratio. Thus, drop deformation experiments with a single drop or cluster of a few drops in a pure extensional flow field are possible. A result of this project is the specification of the time dependence of the deformation in relation to the capillary number describing the ratio between viscous stress and capillary pressure and to the viscosity ratio between drop and matrix fluid.

In this paper we consider the possibility of generating homogeneous flows with a nearly constant strain rate. This is achieved by stretching an almost cylindrical liquid bridge under microgravity. One key issue is the adjustability of the disk diameters, necessary for maintaining ideal boundary conditions. We first study the stretching of two different fluids by both numerical and experimental means. The numerical results are compared with the experimental data and very good agreement is found. The numerical method is then used to study the behaviour of liquid bridges for quite a large range of the flow parameters (capillary number $\Ca$ and Weber number $\We$) in order to detect those regimes with most suitable flow conditions.

Uniaxial extensional flow appears in transport and processing and is able to destroy desired rheological properties of emulsions by tearing drops. During the last few decades, many theoretical approaches used to describe the drop-deformation behaviour of emulsions have involved the assumption that uniaxial extensional flow fields are involved. Recent experiments investigating drop deformation in planar extensional flow fields were restricted to single droplets in a surrounding fluid. The present device considerably improves this situation by allowing one to study the drop-matrix interaction for several drops in uniaxial extensional flow. To determine the deformation of a few drops, a uniaxial flow field with a constant rate of extension with respect to space and time is necessary. This is realized by stretching a large cylindrical liquid bridge under microgravity. The bridge should remain cylindrical throughout the stretching. Therefore, a special mechanical adaptation is used to suppress necking at the ends of the filament. However, bridge deformations caused by viscous stress and by dynamic and capillary pressure gradients still remain. The strain and shear rate distributions in the liquid bridge are evaluated in order to determine the most suitable position for drop-deformation experiments. Examples of several drop-deformation experiments with elliptical and pointed-ends shapes of the stretched bridge are presented.

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Chemie lngenieur Technik (69) 7 I 97 nation der UV-Spektralphotometrie mit einer geeigneten Lichtfaseroptik moglich. Im Gegensatz zur IR-Spektroskopie bietet dabei der W-Bereich den Vorzug, ohne weiteres auch in wasserdampfgesattigten Gasen einsetzbar zu sein. Eine weitere Besonderheit der Laboranlage ist die simultane Untersuchung von Gas und waRriger Losung, wodurch sich auf einfache Weise interessante Einblicke in die in der Fliissigkeit ablaufenden Reaktionen ergeben. Neben der Photometrie werden Analysen flussiger Proben mit Hilfe der Ionenchromatographie durchgefiihrt.Die Apparatur wurde inzwischen zur Messung der SO,-Absorption in Wasser und in warigen Losungen von HCl, H,SO, und CaC1, eingesetzt. Aufbauend auf diesen Ergebnissen wird z. Z. der EinfluR der SO,-Absorption auf geloste Quecksilberverbindungen untersucht. Die Konzentrationen werden stets im Bereich technischer Rauchgas/Wasser-Systeme variiert. Ein wichtiges Ergebnis der bisherigen Untersuchungen ist die Beobachtung, daB die SO, -Absorption durch geloste Chloridionen signifikant beeinflufit wird. Dieser Effekt wird auf der Basis der experimentellen Untersuchung beider Phasen interpretiert. Eine konsistente thermodynamische Modellierung erlaubt schliedlich die hertragung der Laborergebnisse auf komplexe Multikomponentensysteme, wie sie in technischen Anlagen vorliegen.