Slow flow of rigid particle suspensions through simulated stenoses 1

Abstract

Model experiments were conducted in which a suspension of rigid spherical particles of neutral buoyancy in a highly viscous Newtonian fluid was passed through simulated idealized stenoses in a rigid tube under a steady pressure gradient. The ranges of Reynolds numbers (0.3–50), ratio of orifice diameter to tube diameter (1/4–3/4), and particle concentration (0–44 per cent) were selected to compare with values found in the living system. It was found that the pressure drops across the stenoses exceeded the theoretical values somewhat, even with no particles present. The pressure drop increased systematically with particle concentration until particle flow through the stenosis ceased. The flow rate then diminished rapidly as particles accumulated on the upstream side. A Venturi-type stenosis produced considerably higher pressure drops than a corresponding orifice at the same flow rate. However, the Venturi-type stenosis permitted flows with higher particle concentration without plugging. So long as no plugging occurred, it was found that the increase in pressure drop with particle concentration agreed favorably with existing theory if one considers the suspension as a continuum of increased viscosity.