26 research outputs found
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Boger fluid flow through hyperbolic contraction microchannels
This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Boger fluids are characterized by their constant viscosity and elasticity and are very useful to study pure elastic flow behavior. In this paper we assess the potential of a microfluidic hyperbolic contraction as a device to measure the relaxation time of low viscosity polymer solutions, which are difficult to characterize in a conventional capillary break-up extensional rheometer. For this purpose we initially characterize the shear and extensional rheology of aqueous solutions of polyacrylamide (PAA) at different concentrations (400, 250, 125 and 50 ppm) with 1% (w/w) of NaCl, which result in low viscosity Boger fluids. Subsequently, flow visualizations of their flow through a microfluidic hyperbolic contraction were carried out in order to quantify the relation between their degree of elasticity and the vortex growth upstream of the microchannel.Fundação
para a Ciência e a Tecnologia (FCT),
COMPETE and FEDER through projects
PTDC/ EQU-FTT/ 71800/2006, PTDC/EQUFTT/
70727/2006, PTDC/EME-MFE/099109/
2008, REEQ/928/EME/2005 and
REEQ/298/EME/2005
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Microchannels analogues for the study of viscoelastic fluid flows through porous media
This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.This work studies the flow behavior and related pressure losses of viscoelastic polymer solutions in microchannels with two different sequences of contraction/expansion, disposed in a symmetric and an asymmetric arrangement, respectively. These microfluidic devices are proposed as simplified microchannel analogues for the flow of Newtonian and viscoelastic fluids through porous media. The results show that the symmetric configuration mimics the pressure gradient of these polymer solutions through a porous medium at low flow rates (below a critical Deborah number, Decr), while the asymmetric arrangement gives the asymptotic limit at high De values (above Decr) as a consequence of the intrinsic differences in the extensional rate profiles defined by each microgeometry.Fundação para a Ciência e a Tecnologia (FCT),
COMPETE and FEDER through projects
PTDC/ EQU-FTT/ 71800/ 2006, PTDC/EQUFTT/
70727/ 2006, PTDC/ EME-MFE/ 99109/
2008 and REEQ/ 262/ EME/ 2005
Modified Bautista–Manero (MBM) modelling for hyperbolic contraction–expansion flows
In this study, modelling of network-structured material flow is considered through a rounded-corner, hyperbolic 4:1:4 contraction-expansion geometry, under axisymmetric configuration. Three representative constitutive models are adopted to represent networked behaviour and to investigate the flow of wormlike micellar fluids in this context. This includes the MBM model (for base thixotropic properties), some newly proposed micellar models (NM_Ï„p & NM_T; for advanced thixotropic modelling), and the EPPT model (for contrast against non-thixotropic properties). In this configuration, emphasis is placed upon interpretation of flow behaviour for these constitutive models, against their response in simple rheometrical flows. To best determine the factors that contribute to epd-prediction, current findings have also been contrasted against those reported earlier in Lopez-Aguilar et al. [1], for the counterpart abrupt rounded-corner, axisymmetric 4:1:4 contraction-expansion flow