Viscoelastic flow development in planar microchannels

Abstract

central region of the channel is responsible for the generation of the complex flow kinematics. These quantitative results are expected to be useful in optimizing industrial processes and the design of "lab-on-a-chip" devices involving viscoelastic fluids and also have important implications for the applicability of microchannels in complex fluid rheometry.

Viscoelastic microfluidics: progress and challenges

“…Other pronounced phenomena in viscoelastic flows include extrudate swell 62,63 , large vortices and pressure drop when entering contraction geometry 63,64 , and melt fracture 46,62 . In microscale flows, viscoelastic fluids have been reported to exhibit (1) vortex formation at small Reynolds numbers (Re < 0.1) in a contraction microchannel 65 , (2) a longer required entrance length for full development of parabolic velocity profile and concave velocity profile observed during flow development 66 , (3) steady asymmetric flow patterns and unsteady 3D flow patterns in a T-junction microchannel 67 , and (4) suppression of vortex formation downstream obstructions in microchannels 68 .…”

Microfluidic extensional rheometry using stagnation point flow

“…[79][80][81][82] For the same reasons, contraction and expansion flows have remained of significant interest in the era of microfluidics, which owing to the small characteristic length scales allow nonlinear dynamics to be accessed in regimes of large deformation rates (high Wi) and low inertia (low Re) that were unattainable in earlier macroscale pipe flows. [83][84][85][86][87] Although a contraction geometry provides only a transient elongational flow while fluid elements travel through the contraction, the nominal extensional deformation rate _ e is readily controlled via the volumetric flow rate through the contraction. 72,88 The applied fluid strain e is effectively constant for a given device and is approximated by the contraction ratio (i.e., the ratio of upstream to downstream channel cross-sectional area).…”

“…74 Flows of viscoelastic polymer solutions through planar abrupt microfluidic contractions have been quite widely studied experimentally using streak imaging, velocimetry, pressure loss, and flow-induced birefringence (FIB) measurements. 83,84,[86][87][88][89][90] These generally show a sequence of instabilities that develop with increasing flow rates or Wi, beginning with the observation of diverging streamlines upstream of the contraction plane and proceeding through to the development of lip vortices at the reentrant corners, then upstream vortices in the salient corners which grow in size as the Wi is further increased. At higher Wi, time-dependent and three-dimensional (3D) flow instabilities are observed, see Fig.…”

Escoamento Viscoelástico Através De Microcanais Com Constrição

“…O tempo de relaxação estimado através da teoria de Zimm foi menor do que o valor obtido através do CaBER (λCaBER=66ms). Esta discrepância foi reportada também em outras investigações (Rodd et al, 2007(Rodd et al, e 2010, sendo possíveis causas a polidispersidade do polímero na amostra e a concentração não diluída do polímero na solução (Li et al, 2015). Nas investigações de Sousa et al (2011) utilizaram o mesmo polímero de PEO (C=0,1% e PM=8x10 6 g/mol) diluída em água deionizada obtendo os tempos de relaxação de λCaBER=73,9ms e λZimm=10,1ms, sendo bastante próximos de nossos resultados.…”

“…Tomando em conta esse fato e a variação de profundidade da garganta tornam um escoamento de cinemática complexa do que comparado com as geometrias padrão de contrição abrupta planar de profundidade constante e de maiores comprimentos de constrição (Li et al, 2015e Clarke et al, 2015. solução de glicerina.…”