Repositório Comunidade: <p align="justify">The RU came up from the interaction between the former Textile and Paper Materials unit (MTP) and other research groups, from UBI and 4 Polytechnic Institutes (Beja, Bragança, Castelo Branco and Guarda), which allows sharing resources, namely equipments and human resources, for the development of R&D projects of mutual interest.</p><p align="justify">The RU came up from the interaction between the former Textile and Paper Materials unit (MTP) and other research groups, from UBI and 4 Polytechnic Institutes (Beja, Bragança, Castelo Branco and Guarda), which allows sharing resources, namely equipments and human resources, for the development of R&D projects of mutual interest.</p>http://hdl.handle.net/10400.6/4362017-09-21T21:15:24Z2017-09-21T21:15:24ZThe role of adsorption on nanofiltration of azo dyesGomes, Arlindo CaniçoPinho, Maria Norberta dehttp://hdl.handle.net/10400.6/6482016-04-14T10:11:41Z2010-04-28T10:07:37ZTítulo: The role of adsorption on nanofiltration of azo dyes
Autor: Gomes, Arlindo Caniço; Pinho, Maria Norberta de
Resumo: The influence of osmotic pressure and solute adsorption on permeate flux during nanofiltration (NF) of a wool textile dye solution was investigated. Solutions of C.I. Acid Orange 7 with concentrations ranging from 2 to 2000 mg/l were subjected to nanofiltration with a NF45 membrane. An increase of flux decline with dye concentration was observed. The resistance-in-series model gives evidence that the main factor causing this flux decline is the solute adsorption. This is reinforced by the increase in the apparent rejection with dye concentration. Although osmotic pressure was taken into account, its contribution to a decrease of the driving force seems not to be significant. Adsorption resistance was calculated from a correlation between the pure water fluxes, measured before and after the essays, and feed dye concentration. A Langmuir isotherm type curve agreed well with experimental data. From the solution-diffusion model, the intrinsic rejection coefficient can be predicted as function of feed dye concentration.2010-04-28T10:07:37ZOn extensibility effects in the cross-slot flow bifurcationRocha, Gerardo N.Poole, R. J.Alves, Maria Arminda CostaOliveira, Paulo Jorge dos Santos Pimentel dehttp://hdl.handle.net/10400.6/6492016-05-04T16:23:39Z2010-04-28T10:07:37ZTítulo: On extensibility effects in the cross-slot flow bifurcation
Autor: Rocha, Gerardo N.; Poole, R. J.; Alves, Maria Arminda Costa; Oliveira, Paulo Jorge dos Santos Pimentel de
Resumo: The flow of finite-extensibility models in a two-dimensional planar cross-slot geometry is studied numerically,
using a finite-volume method, with a view to quantifying the influences of the level of extensibility, concentration parameter, and sharpness of corners, on the occurrence of the bifurcated flow pattern that is known to exist above a critical Deborah number. The work reported here extends previous studies, in which the viscoelastic flow of upper-convected Maxwell (UCM) and Oldroyd-B fluids (i.e. infinitely extensionable models) in a cross-slot geometry was shown to go through a supercritical instability at a critical
value of the Deborah number, by providing further numerical data with controlled accuracy.We map the
effects of the L2 parameter in two different closures of the finite extendable non-linear elastic (FENE)
model (the FENE-CR and FENE-P models), for a channel-intersecting geometry having sharp, “slightly”
and “markedly” rounded corners. The results show the phenomenon to be largely controlled by the extensional
properties of the constitutive model, with the critical Deborah number for bifurcation tending to be reduced as extensibility increases. In contrast, rounding of the corners exhibits only a marginal influence on the triggering mechanism leading to the pitchfork bifurcation, which seems essentially to be restricted to the central region in the vicinity of the stagnation point.2010-04-28T10:07:37ZThe log-conformation tensor approach in the finite-volume method frameworkAfonso, AlexandreOliveira, Paulo Jorge dos Santos Pimentel dePinho, Fernando Tavares deAlves, Maria Arminda Costahttp://hdl.handle.net/10400.6/6472016-05-04T16:27:03Z2010-04-28T10:07:37ZTítulo: The log-conformation tensor approach in the finite-volume method framework
Autor: Afonso, Alexandre; Oliveira, Paulo Jorge dos Santos Pimentel de; Pinho, Fernando Tavares de; Alves, Maria Arminda Costa
Resumo: The log-conformation formulation, proposed by Fattal and Kupferman [J. Non-Newt. Fluid Mech. 123
(2004) 281], has helped to provide further insights into the High-Weissenberg Number Problem. In this work, we investigate the performance of the log-conformation formulation in the Finite Volume Method
(FVM) framework for creeping flows of viscoelastic fluids in steady and unsteady flows around a confined
cylinder. The Oldroyd-B and Phan-Thien–Tanner (PTT) constitutive equations were used to assess
the effect of different rheological behaviour on the flow patterns and solution stability. The calculation
of the polymer stress contribution is carried out with both the standard technique and with the logconformation
methodology. For all test cases, up to the critical conditions when both methods converge to a steady solution, the use of the log-conformation technique provides solutions with similar accuracy as the standard approach. In terms of stability the log-conformation formulation is found to be significantly
more robust, and solutions could be obtained at higher Deborah number flows.2010-04-28T10:07:37ZPlane contraction flows of upper convected Maxwell and phan-ThienTanner fluids as predicted by a finite-volume methodOliveira, Paulo Jorge dos Santos Pimentel dePinho, Fernando Tavares dehttp://hdl.handle.net/10400.6/6422016-04-12T10:38:21Z2010-04-28T10:07:36ZTítulo: Plane contraction flows of upper convected Maxwell and phan-ThienTanner fluids as predicted by a finite-volume method
Autor: Oliveira, Paulo Jorge dos Santos Pimentel de; Pinho, Fernando Tavares de
Resumo: A finite-volume (FV) procedure is applied to the prediction of two-dimensional (2-D) laminar flow through a 4 : 1 planar contraction of upper convected Maxwell (UCM) and simplified Phan-Thien±Tanner (SPTT) fluids. The method incorporates
general coordinates, indirect addressing for easy mapping of complex domains, and is based on the collocated mesh
arrangement. Calculations with the UCM model at a Reynolds number of 0.01 were carried out with three consecutively refined meshes which enabled the estimation of the accuracy of the predictions of the main vortex characteristics through Richardson's extrapolation. Converged solutions with the first-order upwind differencing scheme for the convective terms
were obtained up to at least De à 8 in the finest mesh, but were limited to De 1, De 3 and De 5 for the fine, medium
and coarse meshes, respectively, when using the second-order linear upwind scheme. The predicted flow patterns for
increasing Deborah numbers with the UCM model resemble the well known lip vortex enhancement mechanism reported in the literature for constant-viscosity fluids in axisymmetric contractions and shear-thinning fluids in planar contraction, but very fine meshes were required in order to capture the described vortex activity. Predictions with the SPTT model also compared well with the behaviour reported in the literature.2010-04-28T10:07:36Z