Start‐up Behavior of Viscoelastic Fluid Flow Near a Capillary Entry

A bstract : The effect of elasticity on the capillary entry flow development process was investigated by applying a laser doppler velocimeter (LDV) and flow visualization. The fluid filling the test section was kept at rest under a pressure of compressed air or a natural head and then a valve below the capillary was quickly opened to start the flow. Although the development of the capillary entry flow field of a Newtonian fluid is virtually quasi‐steady, it takes a considerable time for a viscoelastic PAA‐solution to attain its terminal regime. The transient behavior of the flow rate of the PAA‐solution is attributed to the gradual development process of the flow field upstream from the entry.