Optimized cross-slot flow geometry for microfluidic extension rheometry

A precision-machined cross-slot flow geometry with a shape that has been optimized by numerical simulation of the fluid kinematics is fabricated and used to measure the extensional viscosity of a dilute polymer solution. Full-field birefringence microscopy is used to monitor the evolution and growth of macromolecular anisotropy along the stagnation point streamline, and we observe the formation of a strong and uniform birefringent strand when the dimensionless flow strength exceeds a critical Weissenberg number Wicrit 0:5. Birefringence and bulk pressure drop measurements provide self consistent estimates of the planar extensional viscosity of the fluid over a wide range of deformation rates (26 s1 "_ 435 s1) and are also in close agreement with numerical simulations performed by using a finitely extensible nonlinear elastic dumbbell model

Shear viscosity and nonlinear behaviour of whole blood under large amplitude oscillatory shear

We investigated experimentally the rheological behavior of whole human blood subjected to large amplitude oscillatory shear under strain control to assess its nonlinear viscoelastic response. In these rheological tests, the shear stress response presented higher harmonic contributions, revealing the nonlinear behavior of human blood that is associated with changes in its internal microstructure. For the rheological conditions investigated, intra-cycle strain-stiffening and intra-cycle shear-thinning behavior of the human blood samples were observed and quantified based on the Lissajous–Bowditch plots. The results demonstrated that the dissipative nature of whole blood is more intense than its elastic component. We also assessed the effect of adding EDTA anticoagulant on the shear viscosity of whole blood subjected to steady shear flow. We found that the use of anticoagulant in appropriate concentrations did not influence the shear viscosity and that blood samples without anticoagulant preserved their rheological characteristics approximately for up to 8 minutes before coagulation became significant

Nanogel formation of polymer solutions flowing through porous media

A gelation process was seen to occur when Boger fluids made from aqueous solutions of polyacrylamide (PAA) and NaCl flowed through porous media with certain characteristics. As these viscoelastic fluids flow through a porous medium, the pressure drop across the bed varies linearly with the flow rate, as also happens with Newtonian fluids. Above a critical flow rate, elastic effects set in and the pressure drop grows above the low-flow-rate linear regime. Increasing further the flow rate, a more dramatic increase in the slope of the pressure drop curve can be observed as a consequence of nanogel formation. In this work, we discuss the reasons for this gelation process based on our measurements using porous media of different sizes, porosity and chemical composition. Additionally, the rheological properties of the fluids were investigated for shear and extensional flows. The fluids were also tested as they flowed through different microfluidic analogues of the porous media. The results indicate that the nanogel inception occurs with the adsorption of PAA molecules on the surface of the porous media particles that contain silica on their surfaces. Subsequently, if the interparticle space is small enough a jamming process occurs leading to flow-induced gel formation

O orçamento da Embrapa.

o trabalho discute por que existe pesquisa pública na agricultura, mostra que as taxas de retornos dos investimentos públicos na Embrapa são muito elevadas, o que significa que os investimentos deveriam ser ampliados. A despeito do desempenho marcante do agronegócio, e muito desse desempenho se assentou na modernização da agricultura, em função de tecnologias geradas pela pesquisa pública, os investimentos na Embrapa caíram sensivelmente na década de 1990 e nos primeiros anos da década de 2000. Construiu-se na Embrapa uma infra-estrutura de pesquisa e ela foi equipada com pesquisadores de nível de primeiro mundo, formados e treinados com dinheiro público, e, rapidamente, estão eles perdendo a capacidade de retribuir à sociedade o salário que recebem, porque o investimento em custeio da pesquisa e em laboratórios caiu para níveis muito baixos. Como os salários dos pesquisadores, em termos reais, sofreram depreciação, a empresa não atrai talentos e perde os mais competentes, porque se demitem, e por aposentadoria precoce. Ou seja, ela está ficando menos eficiente, porque lhe faltam meios, e sua sobrevivência está ameaçada. Ou, ainda, segundo a lógica do setor privado, uma empresa está condenada à falência se não for capaz de operacionalizar o seu capital fixo (pessoal + capital físico), com volumes adequados de capital de giro (custeio). Na agricultura, em nenhum país de agronegócio pujante como o brasileiro, a pesquisa da iniciativa particular substituiu os investimentos públicos, e ela mesma foi, em parte, financiada pelo governo, por inter-médio de incentivos e renúncia fiscal. O que a experiência tem demonstrado é que a pesquisa da iniciativa particular é muito mais produtiva nos países que muito investiram em pesquisa pública. Ainda, os investimen-tos em pesquisa pública continuam tendo taxas de retornos elevadas, quando comparados com outras opções. Ou seja, a despeito do crescimento da pesquisa particular, ainda, é ótimo negócio para a sociedade investir em pesquisa pública. O agronegócio se beneficiou dos investimentos de pesquisa do passado e se desenvolveu de forma tão marcante. A pergunta que se faz é qual será seu desempenho, num quadro de queda acentuada dos investimentos públicos na Embrapa

On the effect of contraction ratio in viscoelastic flow through abrupt contractions

A numerical study of the creeping flow of a PTT fluid through planar sudden contractions was carried out to quantify the effect of contraction ratio upon the flow characteristics (streamlines and size and intensity of recirculation vortices). The relevant governing equations were solved with a finite volume method embodying a new high-resolution scheme (Alves et al. [Int. J. Numer. Meth. Fluids 41 (2003) 47]) for the discretisation of convection terms, which is here explained and shown to yield improved accuracy and robustness. The results of the simulations, in terms of streamline patterns, give further evidence for a lip-vortex enhancement mechanism and are in remarkable agreement with flow visualization photographs from the literature. In addition, the results show that the variation of flow features in the vicinity of the re-entrant corner, such as lip vortex size and streamlines, are dominated by downstream quantities and scale with the common definition for the Deborah number in this flow, while flow characteristics in the salient corner region scale with that Deborah number divided by the contraction ratio

Viscoelastic flow in a 3D square/square contraction: Visualizations and simulations.

The inertialess three-dimensional (3D) flow of viscoelastic shear-thinning fluids in a 4:1 sudden square-square contraction was investigated experimentally and numerically and compared with the flow of inelastic fluids. Whereas for a Newtonian fluid the vortex length remains unchanged at low Reynolds numbers, with the non-Newtonian fluid there is a large increase in vortex length with fluid elasticity leading to unstable periodic flow at higher flow rates. In the steady flow regime the vortices are 3D and fluid particles enter the vortex at the middle plane, rotate towards its eye, drift sideways to the corner-plane vortex, rotate to its periphery, and exit to the downstream duct. Such dynamic process is reverse of that observed and predicted with Newtonian fluids. Numerical predictions using a multimode Phan-Thien–Tanner viscoelastic model are found to match the visualizations accurately and in particular are able to replicate the observed flow reversal. The effect of fluid rheology on flow reversal, vortex enhancement, and entry pressure drop is investigated in detail

Reliability and validity of the Chester step test in patients with interstitial lung disease

The Chester Step Test (CST) is a simple and inexpensive field test, which requires minimal physical space to assess exercise capacity. Such characteristics make the CST suitable to be used in different settings, however, its measurement properties in patients with interstitial lung diseases (ILD) are unknown. A cross-sectional study was conducted in patients with ILD. First, a CST-1 and a 6-minute walk test (6MWT) were performed. After 48-72 hours, a CST-2 was repeated. A 2nd rater was present in one of the sessions. Relative reliability was measured using intraclass correlation coefficient (ICC1,1 and ICC2,1). Absolute reliability was determined using standard error of measurement (SEM), minimal detectable change at 95% confidence interval (MDC95) and the Bland-Altman method. The values of SEM and MDC95 were also expressed as a percentage of the mean. Construct validity was explored using Spearman correlation coefficient (rs) between the number of steps taken in the best CST and the distance performed in the 6MWT. Sixty-six patients with ILD (65.5±12.9 years; 48.5%men; FVC 79.4±18.8pp; DLCO 49.0±18.3pp) participated in the study. Relative (ICC 0.95-1.0) and absolute reliability were excellent without evidence of systematic bias. The SEM and MDC95 were 11.8 (14.7%) and 32.6 steps (40.7%), respectively. The correlation between CST and 6MWT was significant, positive, and high (rs=0.85, p=0.001). The CST is a reliable and valid test and might be especially useful to assess exercise capacity in patients with ILD in limited space environments.publishe