ICI - FibEnTech | Documentos por Auto-Depósito
Permanent URI for this collection
Browse
Browsing ICI - FibEnTech | Documentos por Auto-Depósito by Issue Date
Now showing 1 - 10 of 77
Results Per Page
Sort Options
- Plane contraction flows of upper convected Maxwell and phan-ThienTanner fluids as predicted by a finite-volume methodPublication . Oliveira, Paulo J.; Pinho, FernandoA 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.
- Biological treatment of effluent containing textile dyesPublication . Gonçalves, Isolina Maria da Silva Cabral; Amorim, M. T. P.; Porter, R. S.; Gomes, Arlindo Caniço; Ferra, Maria Isabel; Brás, RuiColour removal of textile dyes from effluent was evaluated using a laboratory upflow anaerobic sludge blanket reactor. Several commercial dyes were selected to study the effect of dye structure on colour removal. The anaerobic reactor was fed with glucose, an easily biodegradable organic matter and selected individual dyes. Results show that some of the dyes are readily reduced under anaerobic conditions even at high concentration of 700 mg/l. The average removal efficiency for acid dyes using this method was between 80 and 90% and that observed for the direct used was 81%. Laboratory experiments using the anaerobic reactor with disperse dyes, such as an anthraquinone based dye, were unsuccessful even at low concentrations of 35 mg/l. Additional experiments were conducted to evaluate the toxicity of a selected disperse dye to an anaerobic environment. Results indicate that the purified dye is more toxic to the biomass than the commercial one.
- The rejection of anionic dyes and salt from water solutions using a polypropylene microfilterPublication . Gomes, Arlindo Caniço; Porter, John JeffersonPrevious work reported by this laboratory showed that inorganic membranes such as stainless steel and ceramic microfilters were capable of rejecting anionic dyes and sodium nitrate from water solutions. It was of interest of see if this were possible with organic membranes such as propylene micrifilters. Experimental data are presented showing that propylene microfilter will reject both salt and Direct Red 2 from aqueous solutions when the conductivity of the solution is below 500 microS. The use of microfiltration comprises the largest fraction of the total membrane production in the world and is now use commercially for tertiary biological wastewater treatment. The effect of pH and salt concentration on the filtration rate and color rejection is also presented.
- Enzymatic hydrolysis of Pinus pinaster kraft pulpPublication . Duarte, Ana Paula; Spiridon, Iuliana; Belgacem, Mohamed Naceurkraft pulp from Pinus pinaster was treated with two enzymes preparations - Cartazyme MCX-A (which presents both cellulase and xylanase activity) and Cartazyme PS-10 (a xylanase preparation) to enhance papermaking properties of the fibres. Both preparations reduced Kappa number and improved brightness, while the effect on the papermaking properties was different.
- Design of calibrators for extruded profiles. Part I: modelling the thermal interchangesPublication . Nóbrega, J. M.; Carneiro, Olga; Covas, José A; Pinho, Fernando; Oliveira, Paulo J.The parameters influencing the calibration/cooling stage of profile extrusion are discussed, and a numerical finite-volume method code to model the heat transfer is described and validated. For this purpose, the numerical predictions are compared with the analytical solution of a simple problem, with results available in the literature and with those produced by a commercial software. The routines developed are then used to identify the main process parameters and boundary conditions and to estimate their relative importance. The investigation clearly shows the advantages of using several calibrators separated by annealing zones, relative to a single calibrator of the same total length, and the large impact of the contact resistance between extrudate and cooling unit while showing negligible impact of other boundary conditions. A decrease of the extrudate velocity is seen to be also an effective control parameter, but it decreases the production rates.
- The effect of the presence of surfactantis on kraft pulping of Pinus PinasterPublication . Baptista, Cecília; Belgacem, Mohamed Naceur; Duarte, Ana PaulaIn order to ascertain the influence of the surfactants in the delignification of Pinus pinaster wood and the bleachability of the resulting pulps, 17 surfactants from four families of surfactants were tested, namely: cationic, anionic, non-ionic and amphoteric. The best results in terms of improved delignification, lower screen rejects and lighter unbleached pulps were obtained with the non-ionic surfactants. When compared with the reference, these cookings exhibit a decrease of the pulps kappa number by up to 6.2% and 39% in the case of the screen rejects, and an increase in the unbleached pulps reflectance factor of approximately 9%. The most promising samples in terms of reflectance factor were poly(ethyleneglycol) 1000-4%, block copolymer poly(ethyleneglycol)- poly(propyleneglycol) 1100-4% and poly(oxyethylene) 100 stearyl ether-1%. It was also established that the use of surfactants as cooking additives did not influence the bleachability, but allows savings of chlorine dioxide in the first bleaching stage (about 5.2%), with the consequent environmental and economical benefits.
- The role of adsorption on nanofiltration of azo dyesPublication . Gomes, Arlindo Caniço; Pinho, Maria Norberta deThe 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.
- Monoazo and diazo dye decolourisation studies in a methanogenic UASB reactorPublication . Brás, Rui; Gomes, Arlindo Caniço; Gonçalves, Isolina Maria da Silva Cabral; Pinheiro, H. M.; Ferra, M. I. A.Mixed anaerobic bacterial consortia have been show to reduce azo dyes and batch decolourisation tests have also demonstratedthat predominantly methanogenic cultures also perform azo bond cleavage. The anaerobic treatment of wool dyeing effluents, which contain acetic acid, could thus be improved with a better knowledge of methanogenic dye degradation. Therefore, the decolourisation of two azo textile dyes, a monoazo dye (Acid Orange 7, AO7) and a diazo dye (Direct Red 254, DR254), was investigated in a methanogenic laboratory-scale Upflow Anaerobic Sludge Blanket (UASB), fed with acetate as primary carbon source. As dye concentration was increased a decrease in total COD removal was observed, but the acetate load removal (90%) remained almost constant.Acolour removal level higher than 88%was achieved for both dyes at aHRT of 24 h. The identification by HPLC analysis of sulfanilic acid, a dye reduction metabolite, in the treated effluent, confirmed that the decolourisation process was due mainly to azo bond reduction. Although, HPLC chromatograms showed that 1-amino-2-naphthol, the other AO7 cleavage metabolite, was removed, aeration batch assays demonstrated that this could be due to auto-oxidation and not biological mineralization. At a HRT of 8 h, a more extensive reductive biotransformation was observed for DR254 (82%) than for AO7 (56%). In order to explain this behaviour, the influence of the dye aggregation process and chemical structure of the dye molecules are discussed in the present work.
- Papermaking potential of Acacia dealbata and Acacia melanoxylonPublication . Santos, António J. A.; Anjos, Ofélia M. S.; Simões, RogérioThe pulping and papermaking potential of Acacia dealbata and Acacia melanoxylon were studied using Eucalyptus globulus as a reference. Pulp yield, alkali consumption and delignification in the kraft process, of both species, compare very well with the reference. Pulp yield can be higher than that of E globulus and the residual lignin content lower after cooking, which is in good agreement with the lower lignin and extractives content of the wood samples used. Pulps produced from Acacia have slightly lower fibre length and coarseness and higher fibre width and wet fibre flexibility than E globulus pulps. As a consequence of fibre characteristics, the paper produced from Acacia is denser and exhibits higher tensile and burst strength, and lower tear resistance than that from E globulus, at a given PFI revolution. For the same sheet density E globulus displays higher strength properties, but the consequence of achieving this is a lower drainage rate and higher energy consumption in refining.
- Purely Elastic Flow AsymmetriesPublication . Poole, R. J.; Alves, M. A.; Oliveira, Paulo J.Using a numerical technique we demonstrate that the flow of the simplest differential viscoelastic fluid model (i.e., the upper-convected Maxwell model) goes through a bifurcation to a steady asymmetric state when flowing in a perfectly symmetric ‘‘cross-slot’’ geometry. We show that this asymmetry is purely elastic in nature and that the effect of inertia is a stabilizing one. Our results are in qualitative agreement with very recent experimental visualizations of a similar flow in the microfluidic apparatus of Arratia et al. [Phys. Rev. Lett. 96, 144502 (2006)].