Unstable Flow of Viscoelastic Fluids

Abstract

One equation of oscillation is obtained from both the pressure balance in the reservoir-capillary system and the momentum balance of the jet between the exit of the capillary and some downstream cross section where the velocity of the jet is uniform. Through the examination of this equation, the following results are obtained. (1) The critical shear rate, at which the unstable flow begins to occur, may be defined by the coefficient of the first derivative of this equation. (2) It becomes clear that, the same as in experimental results up to this time, the principal cause of the unstable flow is the flow in the vicinity of the capillary entrance.