Determining extensional viscosity from the measured pressure drop in a capillary rheometer for paint liquids based on fluid dynamic simulations

• A method to evaluate the measured extensional viscosity based on measured pressure drop in a capillary rheometer for dilute polymer liquids • A correction factor is necessary for the measurement, which depends on the Reynolds number in orifice die • The entry flow field, the pressure drop in the capillary rheometer was analyzed by means of numerical simulation • Effects of shear and extensional behaviors can be considered by using the proposed hybrid viscosity model for practical painting applications • Validation between measured and simulated pressure drops in the orifice dies have been performed. The present study deals with generalized Newtonian fluids. A method to evaluate the measured extensional viscosity obtained from the pressure drop of entry flow in a capillary die for dilute polymer liquids has been proposed. It is shown that a correction factor based on a calibration curve, which is dependent on the Reynolds number in orifice die, is necessary for the measured entrance pressure drop by using capillary rheometer. The calibration curve for a given orifice die can be derived by using Newtonian test liquids and the Trouton-ratio and applied to determine the extensional viscosity for dilute polymer liquids. Numerical simulations of pressure drop in orifice dies using Newtonian liquids and paint liquids are carried out. The dependence of the proposed correction factor on the Reynolds number can be explained through the analysis of the entry flow field. The Cross model was applied for fitting the measured viscosity curves. A hybrid viscosity model, considering the effects of shear and extensional behaviors, is proposed for the practical applications. Validation between measured and simulated pressure drops in the orifice dies have been performed.