various radius ratios; Reynold's stresses and bend loss; equisized glass and polystyrene bends; non-Newtonian slurries; geometrical configuration
The flow characteristics in a bend for a single-phase fluid are reasonably well understood and
critically reviewed by Ito (1987). Investigators have established the effect of secondary flows on
bend flow characteristics through measurement of velocity field, Reynold's stresses and bend loss
coefficient at various radius ratios (Hwang & Hita 1987). Studies in bends for a two-phase fluid are relatively few in number. Ayukawa (1968) derived a theoretical relationship for calculating the pressure drop across a bend in a vertical plane in slurry using energy considerations. However, the validity of this relationship is questionable due to the paucity of the experimental data. Toda et al. (1972) investigated the flow through horizontal and vertical pipe bends using suspensions of
equisized glass and polystyrene bends. Their observation was that the flow behavior is complicated due to the presence of secondary flows and that the pressure drop in a horizontal or vertical bend increased with increasing concentration. Kalayanaraman et al. (1973) also investigated through a 90 ° horizontal bend for larger particles at different radii of curvature and established an optimum radius of curvature for minimum pressure loss.
Das et al. (1988) obtained data for pressure drop for different types of horizontal bends for
non-Newtonian slurries at low concentrations to predict pressure loss. Nasr-El-Din & Shook (1987)
suggested that pressure drop and wear are adversely affected by flow disturbances such as those generated in bends. Mukhtar et al. (1993), in their study with multisized particulate slurries, have shown that there is a redistribution of particles belonging to different size fractions, with larger particles being more affected. This phenomenon is more prominent at higher velocities.
The pressure loss in a bend is a strong function of the concentration of solid particles, the pipe
diameter, the mean flow velocity, radius of curvature of bend, bend angle, specific gravity and PSD
of the solid as well as the geometrical configuration of the bend. The data on the pressure drop in bends for a two-phase flow, particularly for multisized particulate slurries, is very limited. Hence in the present work, effort has been made to generate data on bend pressure drop on two materials, namely slurries of iron ore and zinc tailings. These two materials have been chosen because they differed widely in specific gravity as well as particle size distribution.