On disturbances caused by pressure taps in highly elastic flows

The objective of this work is to characterise the onset of laterally asymmetric flow of viscoelastic solutions around a confined microfluidic cylinder, which was encountered in a recent study [Rodrigues et al., $\textit{J. Non-Newton. Fluid Mech.}$ $\textbf{289}$, 104406 (2020)]. To this end, two non-Newtonian fluids were employed in the same micro-geometry. Two microchannels were studied, both with a cylinder of diameter 75 $\mathrm{\mu}$m, aspect ratio (channel height over width) of 0.37 and blockage ratio (cylinder diameter over channel width) of 0.28, differing only on the width of the pressure taps, located 500 $\mathrm{\mu}$m up- and downstream from the respective cylinder face, on opposing walls. The working fluids consist of two poly(ethylene oxide) (PEO) solutions: a weakly shear-thinning elastic fluid and an elastic shear-thinning fluid. Micro-Particle Image Velocimetry ($\mathrm{\mu}$PIV) and streak imaging techniques were used to evaluate the flow over a Weissenberg number range: $100\leq Wi\leq500$, while maintaining a low Reynolds number, $Re<1$. The elastic shear-thinning solution showed laterally asymmetric flow past the cylinder with both pressure tap designs, while with the weakly shear-thinning solution asymmetric flow was only observed with the wider pressure tap intake. In both cases, the fluids preferentially chose the cylinder/wall gap opposing the upstream pressure tap, which was found to influence the flow greatly, seemingly associated with time-dependent flow and possibly the lateral flow asymmetry itself. This work brings to light the necessary compromise between optimal pressure tap design for quality pressure measurements and minimal flow interference, due to the increased susceptibility of elastic microfluidic flows to flow perturbations

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

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

Microfluidic systems for the analysis of the viscoelastic fluid flow phenomena in porous media

In this study, two microfluidic devices are proposed as simplified 1-D microfluidic analogues of a porous medium. The objectives are twofold: firstly to assess the usefulness of the microchannels to mimic the porous medium in a controlled and simplified manner, and secondly to obtain a better insight about the flow characteristics of viscoelastic fluids flowing through a packed bed. For these purposes, flow visualizations and pressure drop measurements are conducted with Newtonian and viscoelastic fluids. The 1-D microfluidic analogues of porous medium consisted of microchannels with a sequence of contractions/ expansions disposed in symmetric and asymmetric arrangements. The real porous medium is in reality, a complex combination of the two arrangements of particles simulated with the microchannels, which can be considered as limiting ideal configurations. The results show that both configurations are able to mimic well the pressure drop variation with flow rate for Newtonian fluids. However, due to the intrinsic differences in the deformation rate profiles associated with each microgeometry, the symmetric configuration is more suitable for studying the flow of viscoelastic fluids at low De values, while the asymmetric configuration provides better results at high De values. In this way, both microgeometries seem to be complementary and could be interesting tools to obtain a better insight about the flow of viscoelastic fluids through a porous medium. Such model systems could be very interesting to use in polymer-flood processes for enhanced oil recovery, for instance, as a tool for selecting the most suitable viscoelastic fluid to be used in a specific formation. The selection of the fluid properties of a detergent for cleaning oil contaminated soil, sand, and in general, any porous material, is another possible application

Microdevices for extensional rheometry of low viscosity elastic liquids : a review

Extensional flows and the underlying stability/instability mechanisms are of extreme relevance to the efficient operation of inkjet printing, coating processes and drug delivery systems, as well as for the generation of micro droplets. The development of an extensional rheometer to characterize the extensional properties of low viscosity fluids has therefore stimulated great interest of researchers, particularly in the last decade. Microfluidics has proven to be an extraordinary working platform and different configurations of potential extensional microrheometers have been proposed. In this review, we present an overview of several successful designs, together with a critical assessment of their capabilities and limitations

Effect of several cryoprotectants on the physicochemical and rheological properties of suwari gels from frozen squid surimi made by two methods

Functionality of squid surimi (Dosidicus gigas) made by two methods (isoelectric precipitation A, and acid washing, B) and stored for 6 months at -15 °C, was analysed as a function of several cryoprotectants. The cryoprotectant effect was studied in terms of the ability to form suwari gels (SA and SB) from the two kinds of surimi. Chemical analyses to detect protein aggregation, dynamic oscillatory tests at constant temperature (10 °C) and temperature sweep tests from 10 to 90 °C were performed. Frozen storage of surimi samples produced two different effects on the thermo-rheological properties of SA and SB suwari gels: in SB samples there were no significant differences over frozen storage. Of the SA samples, the ones with trehalose retained their initial viscoelastic properties best at 10 °C; moreover, trehalose significantly altered the pattern of the thermal gelation profile in SA samples, making it similar to SB samples. All these thermo-rheological results are consistent with protein solubility and electrophoresis (SDS-PAGE) data evidencing protein aggregation. © 2009 Elsevier Ltd. All rights reserved.Peer Reviewe

CorkSTFlfluidics - A novel concept for the development of eco-friendly light-weight energy absorbing composites

CorkSTFlfluidics are environmentally friendly composites consisting of a laminar sheet of compactedmicro-agglomerated cork engraved with a network of microchannels by laser and filled with a concentrated aqueous solution of cornstarch (shear thickening fluid). Thus the mechanical properties of thesecomposites will result from the combination of the mechanical properties of the micro-agglomeratedof cork and the enhanced shear thickening response of the STF flowing through the network ofmicrochannels. In this work we have performed low velocity impact tests using a drop weight testingmachine in order to asses the improvement of these composites with regards to the micro-agglomeratedof cork alone. A numerical analysis was also performed and allowed to understand how shear thickeningbehavior is triggered by the appropriate combination microchannels' size and the inlet velocity. Thus, forthe 60P/40S/M sample, the peak force was larger than the one given by the cork sheets without engravedmicrochannel nor STF

Gelation process in two different squid (Dosidicus gigas) surimis throughout frozen storage as affected by several cryoprotectants: Thermal, mechanical and dynamic rheological properties

Differential scanning calorimetry (DSC) was used to follow the thermal denaturation of two differently processed surimis from giant squid (Dosidicus gigas), A (isoelectric precipitation) and B (acid washing). Both surimis were added with several cryoprotectants (sucrose, sorbitol and trehalose), and kept in frozen storage at -15 °C for 6 months. DSC profiles and transition enthalpies showed that protein quality was better in B than in A surimis whether fresh or frozen. It was also demonstrated that the sucrose-plus-sorbitol mixture and trehalose were the most efficient for preserving B and A type formulations respectively after frozen storage. Mechanical (puncture), small amplitude oscillatory (SAOS) and dynamic-mechanical thermoanalyses were performed on both gels from A and B series surimis throughout frozen storage. Gels from surimi A (GA) were considerably brittler than gels from surimi B (GB) and presented significantly lower strain amplitudes. Several correlations among different experimental data have been developed. © 2011 Elsevier Ltd. All rights reserved.This work has been supported by Spanish Ministerio de Ciencia y Tecnología under project AGL-04892-C03-03ALI.Peer Reviewe

Rheological study of giant squid surimi (Dosidicus gigas) made by two methods with different cryoprotectants added

Two new methods were designed for making surimi from giant squid (Dosidicus gigas) muscle. The first is based on protein precipitation at the isoelectric point (type A), and the second on washing with an acid solution (type B). Chemical analyses (e.g. protein solubility, electrophoretic profile), structural analyses (scanning electronic microscopy) and above all rheological analyses were carried out. Small amplitude oscillatory tests were performed to evaluate the influence of these two methods on the viscoelasticity and gel-forming ability of squid surimi. The results showed that method B preserves the functionality of the myofibrillar proteins better, thus making for a better gel structure than method A. Moreover, the addition of different cryoprotectants (sorbitol + sucrose, sorbitol + trehalose, trehalose alone), resulted in essential differences between the two kinds of surimi. In surimi A, trehalose favoured less initial protein aggregation and hence a thermorheologically stable structure, with a better gelation profile than sorbitol + sucrose or sorbitol + trehalose, in surimi, suwari-gels and definitive-gels alike. However, in B samples the influence of different cryoprotectants was not discernible. © 2009 Elsevier Ltd. All rights reserved.This work has been supported by the Spanish Ministerio de Ciencia e Innovación under Project AGL2005-04347Peer Reviewe

In vitro particulate analogue fluids for experimental studies of rheological and hemorheological behavior of glucose-rich RBC suspensions

Suspensions of healthy and pathological red blood cells (RBC) flowing in microfluidic devices are frequently used to performin vitroblood experiments for a better understanding of human microcirculation hemodynamic phenomena. This work reports the development of particulate viscoelastic analogue fluids able to mimic the rheological and hemorheological behavior of pathological RBC suspensions flowing in microfluidic systems. The pathological RBCs were obtained by an incubation of healthy RBCs at a high concentration of glucose, representing the pathological stage of hyperglycaemia in diabetic complications, and analyses of their deformability and aggregation were carried out. Overall, the developedin vitroanalogue fluids were composed of a suspension of semi-rigid microbeads in a carrier viscoelastic fluid made of dextran 40 and xanthan gum. All suspensions of healthy and pathological RBCs, as well as their particulate analogue fluids, were extensively characterized in steady shear flow, as well as in small and large amplitude oscillatory shear flow. In addition, the well-known cell-free layer (CFL) phenomenon occurring in microchannels was investigated in detail to provide comparisons between healthy and pathologicalin vitroRBC suspensions and their corresponding analogue fluids at different volume concentrations (5% and 20%). The experimental results have shown a similar rheological behavior between the samples containing a suspension of pathological RBCs and the proposed analogue fluids. Moreover, this work shows that the particulatein vitroanalogue fluids used have the ability to mimic well the CFL phenomenon occurring downstream of a microchannel contraction for pathological RBC suspensions. The proposed particulate fluids provide a more realistic behavior of the flow properties of suspended RBCs when compared with existing non-particulate blood analogues, and consequently, they are advantageous for detailed investigations of microcirculation.The authors acknowledge the financial support provided by Fundac¸~ao para a Ci^encia e a Tecnologia (FCT), COMPETE, and FEDER through the Ph.D. scholarship SFRH/BD/89077/2012, Grant IF/00148/2013, and project POCI-01–0145-FEDER-016861 (with associated reference PTDC/ QEQ-FTT/4287/2014) funded by COMPETE2020—Programa Operacional Competitividade e Internacionalizac¸~ao (POCI) with the financial support of FCT/MTES through national funds (PIDDAC) and by the project Nos. PTDC/EQU-FTT/118716/2010, EXPL/EMS-SIS/2215/2013, UID/EMS/00532/2013, and UID/EMS/04077/2013.info:eu-repo/semantics/publishedVersio