Abstract
A flow near a die entry or in an abruptly contracting pipe flow is one of flows where elasticity of fluid can have dominant effect because a fluid element is elongated unsteadily even when the flow field itself is steady. This investigation is focused on the effect of elasticity on the development process of a capillary entry flow. An aqueous solution of polyacrylamide with a concentration of 0.2wt% was used as the viscoelastic test fluid. The start-up behavior of entry flow to a pipe of 2mm inner diameter attached to the bottom of a large reservoir was investigated by applying flow visualization and LDV. While the developing process of capillary entry flow of a Newtonian fluid is virtually quasi-steady, it takes a considerable time for a viscoelastic fluid to attain its terminal regime. The flow pattern upstream the capillary entry determines the elongation rate, which governs the elongation stress at the entry, and the entry pressure loss in turn. Hence, the transient behavior of the flow rate is attributed to the gradual development process of the flow field upstream the entry.
