Chairmen: J. Kubie, A. Valle


Volkhard Köhler, Martin Vorbach, Christian Weiß, and Rolf Marr
Institute of Chemical Engineering and Environmental Technology
Graz University of Technology, A-8010 Graz, Austria

INTRODUCTION The behaviour of droplet swarms in liquid-liquid dispersions, especially found in extraction columns of the RDC-type, was analysed by means of a new fluorescence measurement technique, which represents an extension to the capillary suction method (Pilhofer and Miller, 1972). The measuring principle developed gains profit of the detectable emission light intensity of a fluorescent dye even in trace concentration. An addition of this nontransferring dye to the dispersed phase enables the in-situ determination of bivariate drop size / drop concentration distributions, which provides important information on droplet history for the evaluation of coalescence and break-up rates. Furthermore, the measuring method represents a new approach for the measurement of droplet size dependent residence times in extraction columns.


A small volume of the droplet dispersion is continuously sampled through a glass capillary tube on which an optical device is mounted. With the help of two light beams crossing the capillary perpendicularly to the probe axis tracer concentration in the drops, droplet volume and suction velocity is measured simultaneously. The determination of drop-concentration is based on the fluorescence intensity measurement of a nontransferring fluorescent dye within the drop. A light beam of a specific wavelength is exciting the tracer to emit a concentration-proportional light signal. The measurement and storage of the signal height is realised by transforming the fluorescence light intensity signal to an electrical signal by means of a photomultiplier.

The transmission light intensity of the excitation light beam shows series of rectangular pulses caused by the difference of the refractive index between the continuous and the dispersed phase slugs. Time-of-passage of a drop is detected from the width of the corresponding rectangular pulse. A transmission light beam located 2 mm appart from the first one produces a second pulse signal. The time shift between both signals allows the calculation of the suction velocity and in combination with the time-of-passage of the drop the droplet volume.


Pilot-sized column experiments were conducted in an extraction column of the RDC-type. The organic inlet stream (kerosine) was split into two streams of equal flow rates, one supplied with the fluorescent dye. The intensity of the drop concentration equalization process within the droplet swarm along the column height is a function of the drop interaction rates. Measurements of the bivariate drop size / drop concentration distributions along the column height at steady-state operation enables an extension of the experimental data for the testing of different rate-formulations for drop coalescence by means of a hydrodynamic model. The model developed here is a discrete, stochastic model based on the Drop Population Balance and allows the simulation of drop size and drop tracer distributions along the column height. With the help of a Dynamic Process Simulation tool the estimation of drop size specific coalescence rates is possible.


The ability to measure two independent characteristics for each droplet in combination with a nontransferring tracer enables the determination of drop size specific recidence times. These times were determined for the case of an extraction process without mass transfer, i.e. coalescence and break-up can be neglected, as proved by measurements described above. Feeding the column with dispersed phase droplets of different size classes and producing a step input function concerning the concentration of the droplets, the response concentration function of each droplet class, measured at the top of the column, leads to a mean residence time for droplets of this size. Drop size specific dispersion intensity was analysed too.


Y. Hagiwara, T. None, M. Nakamura, M. Tanaka and H. Hana
Dept. of Mechanical and System Eng., Kyoto Institute of Technology
Matsugasaki, Kyoto 606, Japan

This study aims at understanding the interaction between a vortex in a liquid flow and an immiscible droplet inside the vortex. Experiment has been conducted around a silicon-oil droplet of 6 mm in diameter carried by water Taylor-vortex flow in an annulus between a stationary cylinder of 80 mm in inner diameter and a rotating cylinder of 60 mm in outer diameter. The time-varying velocity field has been visualised by tracer particles smaller than 0.3 mm in diameter. The velocity vectors of the particles have been obtained from visualised images by using a particle-tracking-velocimetry method. Experimental results show that the deformation of the contour lines of two-dimensional kinetic energy is clearly noticeable near the upper part of the interface where the outward radial flow disappears. This means that the attenuation of kinetic energy occurs in the form of diminishing the outward flow. The vorticity is found to be attenuated in almost all area around the droplet except for the small zone where the outward radial flow directly impinged the interface.


Konstantin A. Nadolin
Mechanical and Mathematical Department
Rostov State University, Rostov-on-Don, Russia

ABSTRACT. The goal of this communication is to present some numerical results obtained for penetrative convection model proposed by G.Veronis1. The problem has a significant interest in theory of hydrodynamic stability 1-6 and describes the onset of the convection in water near 40C.


  1. Veronis, G., Penetrative convection; Astrophys.J., Vol. 137, No.2, pp 641–663, 1963.
  2. Debler, W.R., On the analogy between thermal and rotational hydrodynamic stability, J. Fluid Mech., Vol. 24, No.1, pp 165–176, 1966.
  3. Rintel, L., Penetrative convective instabilities, Phys. Fluids, Vol. 10, No.4, pp 848–854, 1967.
  4. Moore, D.R. and Weiss, N.O., Nonlinear penetrative convection, J. Fluid Mech.,Vol. 61, No.3, pp 553–581, 1973.
  5. Musman, S., Penetrative convection, J. Fluid Mech., Vol. 31, No.2, pp 343–360, 1968.
  6. Lin, C.C., The Theory of Hydrodynamic Stability, Cambridge University Press, 1955.


A Prasinos and J Kubie*
School of Mechanical and Manufacturing Engineering
Middlesex University, London N11 2NQ, England


Outflow of liquids from single outlet vessels has been recently investigated by several authors. In such vessels the liquid leaving the vessel through the outlet is replaced by another fluid, either gas or a lighter liquid, entering the vessel through the same opening. The simplest example of such an arrangement is an ordinary bottle, which is being emptied of its contents. The majority of the reported work concentrated on cases when water is being replaced by air, but work on two liquid systems has been recently reported, in which water was discharging into, and being replaced by, parafin.

All the investigations on the gas-liquid flow noted the oscillatory character of the flow and identified flooding of the outlet as the controlling mechanism governing the flow. The oscillations of the flow in the case of gas-liquid flows are due to the compressibility of the gas. The compressibility of the gas is used to develop full equations of motion, which are similar to second order non-linear differential equations which govern self-excited oscillations in many mechanical systems. More recent experimental work has been concentrated on the investigation of well defined systems. These systems consisted of an axisymmetric arrangement of a vertical perspex cylindrical vessel with a sealed top and a central outlet in its base. The vessel was initially completely filled with water and the outlet sealed with a stopper. The outlet was then opened by removing the stopper, which allowed the discharge of water from the vessel and the ingress of air. The variation of the void fraction of air in the vessel as a function of elapsed time was then measured. The most significant experimental result was that for a wide range of conditions the void fraction was a linear function of time. The experimental results were described by the flooding parameter C.

A theoretical model for the gas-liquid outflow from single outlet vessels has recently been developed. The model provides an explanation for many of the flow phenomena observed in gas-liquid systems, in particular the linear relationship between the void fraction and the elapsed time and the pressure variation in the gas space above the interface in the sealed vessel.

An experimental investigation of a liquid-liquid system recently reported has shown that even in these systems the void fraction of the lighter phase in the vessel is a linear function of the elapsed time, and that the experimental results can also be described by using the flooding parameter C. It has been also shown that the flooding parameter for the liquid-liquid flow is in a close agreement with the flooding parameter for the gas-liquid flow, provided the usual correction for the fluids densities are taken into account. It is not clear why there is such an agreement between gas-liquid and liquid-liquid flows, since some of the phenomena observed are quite different. Whereas the compressibility of the lighter phase in the case of the gas-liquid systems is very high and determines the behaviour of the system, the compressibility of the lighter phase in the case of the liquid-liquid systems is practically negligible. Hence other mechanisms must be considered in the development of the model.

Further and more detailed experimental work for the outflow of water from a vertical cylindrical vessel into parafin is performed and the variation of the void fraction of parafin in the vessel with the elapsed time obtained. A theoretical model of the outflow, based on a simple physical description of the system, is then developed. The model contains several parameters, which are not measured directly and which must be estimated.

The theoretical model developed in this work for the liquid-liquid flow from single outlet vessels is in reasonable agreement with the experimental data. In particular, the model shows that, as observed experimentally, the void fraction of the lighter phase in the working vessel is a linear function of the elapsed time. Similarly, and as discussed above, the recently developed model of gas-liquid flow from single outlet vessels also shows that the void fraction of the lighter phase in the vessel is a linear function of the elapsed time, as also observed experimentally.

This is rather surprising since the basic mechanisms of the two models are fundamentally different. Whereas the theoretical model for the case of liquid-liquid flow neglects the compressibility of the lighter phase, the theoretical model for the case of gas-liquid flow is based on the compressibility of the lighter phase. This leads to steady-state counter current flow of the two phases through the outlet for the case of liquid-liquid flows, and to a dynamic oscillatory behaviour with just one phase in the outlet at any one time for the case of gas-liquid flows. Furthermore, the flow of the lighter phase is always upward for the case of liquid-liquid flows, but can be both upward and downward, depending on the stage in the oscillatory cycle, for the case of gas-liquid flows.

It is interesting to note that these two different mechanisms provide the explanation for the linear relationship between the void fraction of the lighter phase and the elapsed time for both extremes of the lighter fluid behaviour: incompressible liquid in one case and compressible gas in the other. Furthermore, even though the flooding parameter C provides the means for correlating the experimental data for both extremes of the lighter fluid behaviour, neither model uses the flooding parameter to describe the flow processes involved.

Nevertheless, further work is required to develop the model. In particular, it would be useful to examine those two fluids systems in which the compressibility of the lighter phase is between the two extremes examined in this work.

* Present address: Department of Mechanical, Manufacturing & Systems Engineering, Napier University, 10 Collinton Road, Edinburgh EH10 5DT, Scotland

Future Meetings | Past Meetings | Proceedings on Sale | Related Links

ICHMT World Wide Web Administrator