Planar Elongational Rheometry Using Slit Entry Flow in Hele-Shaw Cell

In our previous study, we observed Hele-Shaw flows of two solutions of a polymer material around two cylinders and through two slits with different lengths. Based on the results, we showed that the potential flow analogy by the Hele-Shaw flow holds when the flow rate is very low in spite of the shear-thinning viscosity and elasticity of the fluids in steady shear flow. It was suggested that the potential flow pattern of the polymer solutions in the Hele-Shaw cell is disturbed by the effect of elongational stress. In this study, a simple method for planar elongational viscosity measurement is devised using the converging flow upstream the slit entry; the elongation rate is estimated from dye streak pattern in the inflow region formed upstream the slit entrance and the elongational stress is obtained from integrated equations of motion. The planar elongational rheometry presented in this work is advantageous due to its applicability to mobile fluids, in addition to its simple experimental set up.