Effects of contraction ratio of continuous abrupt contraction–expansion microchannels on flow regime of polyethyleneoxide solutions affected by memory and scission of polymers

This study experimentally observed the flow regime transitions of polyethylene oxide solutions in continuous abrupt contraction–expansion microchannels with different contraction ratios. The flow regimes and normalized vortex lengths in the contraction and expansion parts of each cavity were provided for various dilute solutions (0.5 × 10−3 wt.% to 1.5 × 10−3 wt.%) and flow rates. By comparing the flow regimes, normalized vortex lengths, and extensional rates across four different channels, the effects of channel dimensions on polymer memory and scission were analyzed. The results show that the contraction ratio is the most critical factor determining flow regime transitions. Higher contraction ratios result in greater extensional rates, leading to faster polymer stretching, more intense scission, and quicker flow regime transitions. In lower contraction ratio channels, the polymer memory effect lasts longer, and scission is more gradual, leading to slower flow transitions. Additionally, channels with longer throat lengths are more prone to elastic instabilities in the contraction part, but the nearly identical trends in normalized vortex length and extensional rate indicate that longer throat lengths have a limited effect on the degree of polymer scission.