Flow of suspensions through tubes—X

Abstract

The translational velocities, paths and deformation of liquid drops in mono disperse emulsions flowing through rigid tubes of 1 cm radius at particle Reynolds numbers < 10⁻⁵ have been measured. The mean drop radii varied from 0.042 to 0.055 cm, the mean linear flow rates from 0.004 to 0.1 cm sec⁻¹ and the volume concentrations from 14 to 37 per cent.

As previously found in suspensions of rigid spheres, the velocity distributions at a given volume flow rate were blunted at concentrations above 25 per cent with partial plug flow developing in the core of the tube. However, the extent of plug flow at a given concentration and particle size was smaller in the emulsions and decreased with increasing flow rate, and at a given flow rate, with increasing suspending phase viscosity. When the emulsions were broken up by stirring the mean drop radius decreased to 5 × 10⁻³ cm and the velocity profiles were parabolic at all flow rates.

The deformed drops migrated away from the tube wall at rates which fluctuated as particles collided with each other, and decreased to zero in the core of the tube. Here, in the particle crowded suspension, the drop paths were also subject to sideways fluctuations and the particles were distorted as they squeezed past each other. In contrast to rigid sphere suspensions, the paths were not reversible when the flow was reversed.

Comparison with data obtained in human ghost cell and red cell suspensions showed that at given values of the shear deformation parameter, the degree of blunting of the velocity profile was similar in the different systems.