Pressure drop enhancement in a concentrated suspension flowing through an abrupt axisymmetric contraction-expansion

Abstract

In this work, we investigate the pressure drop of concentrated suspensions flowing through a 4:1:4 axisymmetric contraction-expansion at low Reynolds number. Pressure drop measurements across the narrow tube show an enhanced pressure drop relative to a Newtonian fluid at the same flow rate. A linear increase in pressure drop as a function of flow rate is observed for the suspensions, with a steeper slope at higher particle volume fraction. However, due to shear-induced particle migration, the pressure drop at each concentration is lower than would be expected for a uniform Newtonian fluid of the same viscosity as the bulk suspension viscosity. The Krieger ͓I. M. Krieger, Adv. Colloid Interface Sci. 3, 111 ͑1972͔͒ expression for the relative viscosity provides an accurate estimate of the dependence of the normalized suspension pressure drop on particle volume fraction, although the bulk suspension viscosity follows the more rapidly increasing curve of Zarraga ͓I. E. Zarraga, D. A. Hill, and D. T. Leighton, J. Rheol. 44, 185 ͑2000͔͒. As the particle volume fraction increases, the normalized pressure drop rises in a similar manner to the area of the recirculation regions in the corner of the expansion and also to the ratio of suspension viscosities in the tube center and recirculation regions. The pressure measurements, along with nuclear magnetic resonance imaging results, suggest that the viscosity ratio between the center and recirculation regions of the suspension, recirculation region size, and pressure drop are all related in contraction-expansion flows of suspensions.

Structural Evolution of Colloidal Gels During Constricted Microchannel Flow

“…The flow of colloidal suspensions within confined geometries is ubiquitous, with examples ranging from blood flow through vascular networks − to material assembly methods such as inkjet printing , and direct-write assembly. − Recent experiments have quantified the flow profiles of suspensions in uniform microchannels using microparticle imaging velocimetry, , fluorescence correlation spectroscopy, and nuclear magnetic resonance imaging. − However, those techniques do not provide information about suspension structure during flow. Quite recently, the structural evolution of aggregates during constricted flow has been characterized by small-angle light scattering .…”

Shear-induced particle migration in the flow of particle suspensions through a sudden plane expansion

“…The particular case of suspensions of particles flowing through sudden expansions and bifurcations has important applications in manufacturing and biological processes, such as in blood cell separation methods [55][56][57]. As a matter of fact, some experimental works have investigated both velocity and particle concentration fields in these geometries [58][59][60][61][62][63]. However, the effect of particle migration on the flow characteristics has not been explored in this geometry.…”