Turbulent flow of liquid-liquid dispersions : drop size, friction losses, and velocity distributions

by Ward, John Philip

The momentum transfer characteristics of liquid-liquid dispersions

were studied under conditions of turbulent flow in a cirular

conduit. Experiments were conducted to obtain drop size, friction

factors and velocity profiles for three organic phases dispersed in

water.

The test sections consisted of straight copper tubes 1-inch OD

and 0.830-inch ID. The velocity profiles and drop size measurements

were made at a point 8-1/2 feet downstream from the entrance

to these tubes. The dispersions were formed and maintained by the

mixing action of a high speed centrifugal pump. The organic phases

were a light petroleum solvent, a light oil and a heavy oil with viscosities

of 1, 15, and 200 centipoise, respectively. Flow rates were

in the range 1-4 lb/sec and concentrations from 5 to 50 volume

percent were studied.

A photographic method of drop size determination was developed.

Excellent results are obtained for drop diameters in the range

5-800 microns. Dispersions with concentrations from 1 to 50 volume

percent were photographed. The drop size and the shape of the drop

size distributions depended strongly on dispersed phase viscosity.

The range of drop diameters was found to increase with dispersed

phase viscosity.

Velocity profile data were obtained in the turbulent core for

three flow rates and four concentrations for the light oil dispersions

and two flow rates and three concentrations for the heavy oil dispersions.

The light oil dispersions were found to behave as single phase

Newtonian fluids. The solvent dispersions have previously been

shown to behave as single phase Newtonian liquids. The heavy oil

dispersions did not behave as Newtonian fluids. These results were

combined with the drop size data and a previously proposed criteria

for treating dispersions as single phase fluids to give the relation

[see PDF for formula] where d?? is the Sauter mean diameter of the dispersed drops.

Dispersions which do not meet this criterion are presumed to have a

"slip" velocity, i.e., the larger drops move relative to the fluid

element in which they are contained. Thus they do not behave as a single phase fluid.

The velocity profiles for the light oil dispersions were used to

calculate an effective dispersion viscosity [mu subscript e]. The viscosity increased

with dispersed phase concentration. Effective viscosities

for the solvent dispersion had been determined by previous workers.

A comparison of the viscosities and drop size data for these two

systems shows that at equal concentrations the effective viscosity of

a dispersion is a function of the drop size distribution, decreasing

with increasing size range. Effective viscosities for the heavy oil

dispersions were determined from the friction factor data and

appeared to be independent of concentration in the range 5 to 17

volume percent. This may be explained by a "slip" velocity and an

analysis of the drop size distributions.

A study was made of one water-in-solvent dispersion and it

was found that water droplets adhered to the pipe wall. The average

size of these droplets could be determined from the observed friction

factor data. The droplets adhering to the wall were observed to

undergo coalescence with the droplets in the flowing dispersion.

Several other observations made through the optical portion of the

photographic arrangement tend to support the coalescence theory

recently proposed by Howarth.