Affiliations: Institute of Medical and Dental Bioengineering, University of Liverpool, PO Box 147, Liverpool L69 3BX, England
Note: [] Accepted by: Editor S. Oka
Abstract: Pressure drop and pressure gradient were measured in steady Newtonian and non-Newtonian flow through tapered tubes having angles of taper, α, between 0.5° and 1.25°. Aqueous solutions of polyacrylamide, characterized as power law fluids, were used for the non-Newtonian flow measurements. These solutions had power law parameters similar in magnitude to those of blood. The pressure drop-flow rate data compared well with the predictions of a semi-empirical flow model over a large range of flow rate (Reα up to 10 for Newtonian flow and 5.7 for non-Newtonian flow). The pressure gradient increased with distance, z, into the taper as the radius decreased. The linear relationship between pressure gradient and z, derived by Oka (Biorheology, 10, 207-212, 1973) was found to be valid only when αz was small. For the tapered tubes examined here, agreement was confined to the region near the inlet. If higher order terms in αz were taken into account the agreement was extended further into the taper. However, under higher flow conditions, when the inertial losses are not negligible, the semi-empirical model provides much better estimates of pressure gradient.
