EXTENSIONAL FLOW OF SEMIDILUTE SUSPENSIONS OF ROD-LIKE PARTICLES THROUGH AN ORIFICE

This paper deals with the extensional flow of semidilute suspensions o f non-Brownian rod-like particles through an orifice. The experimental setup allows simultaneously visualizations of the flow pattern and me asurements of the flow rate-pressure drop relation. The flow pattern i n the converging region is characterized by the appearance of a vortex ring which grows with the volume fraction of the particles and the as pect ratio. At the same time, the pressure drop experienced by the sus pension as it flows through the orifice increases. The experimental re sults are interpreted in terms of a competition between the shear stre ss due to the solvent and the extensional stress generated by the part icles. This interpretation is supported by the scaling of the vortex s ize and of the pressure drop with the volume fraction and the aspect r atio of the particles. (C) 1995 American Institute of Physics.