Measurement of pressure loss and observation of the flow field in viscoelastic flow through an undulating channel

The viscoelastic flow through undulating channels is experimentally studied by using 0.1 and 1.0 wt% aqueous solutions of polyacrylamide (PAA). In the measurement of the pressure loss, it is confirmed that the excess pressure loss occurs for both concentrations of PAA. However, the magnitude of the excess pressure loss for the 1.0 wt % solution of PAA is much smaller than that for the 0.1 wt % of PAA. The Deborah number at the occurrence of the e xcess pressure loss is within the range of 0.1-0.4 and it depends on the co ncentration of PAA and channel geometry. The flow pattern changes to an asy mmetric one including a small disturbance when the excess pressure loss occ urs. Flow unsteadiness observed in the 0.1 wt % solution of PAA is discusse d in connection with the excess pressure loss. In the velocity measurement, an asymmetric character of measured profiles for the velocity provides evi dence for its three-dimensional character. The variation of the stretch rat e on the center line of an undulating channel indicates a significant phase shift beyond the occurrence of the excess pressure loss. (C) 2000 The Soci ety of Rheology. [S0148-6055(00)01001-4].