Reabilitação térmica de fachadas

As fachadas são um elemento da envolvente que faz a interface entre o ambiente exterior e o interior. Do conjunto das suas características mais relevantes, existe uma, cuja importância tem vindo a aumentar devido à conjuntura ambiental e económica atual: o desempenho energético. Assim, é importante analisar as características do comportamento térmico dos elementos da fachada, com base na respetiva regulamentação em vigor (REH – D.L. n.º 118/2013 de 20 de Agosto) e analisar o contributo da sua eventual reabilitação para uma melhor qualidade térmica da fachada e por consequente uma melhor qualidade de conforto dos utentes do edificio, não desprezando o aspeto arquitetónico do mesmo. Esta monografia baseia-se na análise de casos práticos de diferentes soluções construtivas e avaliação das vantagens e desvantagens dos sistemas propostos, conferindo a possibilidade de optar pelo sistema mais eficaz de acordo com as necessidades exigidas. Assim, e com base no principal objetivo, que é o de melhorar o desempenho térmico das fachadas recorrendo à reabilitação, o enfoque é sobre a redução do consumo energético dos edificios, nomeadamente através do contributo térmico dos elementos das fachadas para a redução das necessidades energéticas por climatização.

A study into the permeability and compressibility of Australian bagasse pulp

This is an experimental study into the permeability and compressibility properties of bagasse pulp pads. Three experimental rigs were custom-built for this project. The experimental work is complemented by modelling work. Both the steady-state and dynamic behaviour of pulp pads are evaluated in the experimental and modelling components of this project. Bagasse, the fibrous residue that remains after sugar is extracted from sugarcane, is normally burnt in Australia to generate steam and electricity for the sugar factory. A study into bagasse pulp was motivated by the possibility of making highly value-added pulp products from bagasse for the financial benefit of sugarcane millers and growers. The bagasse pulp and paper industry is a multibillion dollar industry (1). Bagasse pulp could replace eucalypt pulp which is more widely used in the local production of paper products. An opportunity exists for replacing the large quantity of mainly generic paper products imported to Australia. This includes 949,000 tonnes of generic photocopier papers (2). The use of bagasse pulp for paper manufacture is the main application area of interest for this study. Bagasse contains a large quantity of short parenchyma cells called ‘pith’. Around 30% of the shortest fibres are removed from bagasse prior to pulping. Despite the ‘depithing’ operations in conventional bagasse pulp mills, a large amount of pith remains in the pulp. Amongst Australian paper producers there is a perception that the high quantity of short fibres in bagasse pulp leads to poor filtration behaviour at the wet-end of a paper machine. Bagasse pulp’s poor filtration behaviour reduces paper production rates and consequently revenue when compared to paper production using locally made eucalypt pulp. Pulp filtration can be characterised by two interacting factors; permeability and compressibility. Surprisingly, there has previously been very little rigorous investigation into neither bagasse pulp permeability nor compressibility. Only freeness testing of bagasse pulp has been published in the open literature. As a result, this study has focussed on a detailed investigation of the filtration properties of bagasse pulp pads. As part of this investigation, this study investigated three options for improving the permeability and compressibility properties of Australian bagasse pulp pads. Two options for further pre-treating depithed bagasse prior to pulping were considered. Firstly, bagasse was fractionated based on size. Two bagasse fractions were produced, ‘coarse’ and ‘medium’ bagasse fractions. Secondly, bagasse was collected after being processed on two types of juice extraction technology, i.e. from a sugar mill and from a sugar diffuser. Finally one method of post-treating the bagasse pulp was investigated. The effects of chemical additives, which are known to improve freeness, were also assessed for their effect on pulp pad permeability and compressibility. Pre-treated Australian bagasse pulp samples were compared with several benchmark pulp samples. A sample of commonly used kraft Eucalyptus globulus pulp was obtained. A sample of depithed Argentinean bagasse, which is used for commercial paper production, was also obtained. A sample of Australian bagasse which was depithed as per typical factory operations was also produced for benchmarking purposes. The steady-state pulp pad permeability and compressibility parameters were determined experimentally using two purpose-built experimental rigs. In reality, steady-state conditions do not exist on a paper machine. The permeability changes as the sheet compresses over time. Hence, a dynamic model was developed which uses the experimentally determined steady-state permeability and compressibility parameters as inputs. The filtration model was developed with a view to designing pulp processing equipment that is suitable specifically for bagasse pulp. The predicted results of the dynamic model were compared to experimental data. The effectiveness of a polymeric and microparticle chemical additives for improving the retention of short fibres and increasing the drainage rate of a bagasse pulp slurry was determined in a third purpose-built rig; a modified Dynamic Drainage Jar (DDJ). These chemical additives were then used in the making of a pulp pad, and their effect on the steady-state and dynamic permeability and compressibility of bagasse pulp pads was determined. The most important finding from this investigation was that Australian bagasse pulp was produced with higher permeability than eucalypt pulp, despite a higher overall content of short fibres. It is thought this research outcome could enable Australian paper producers to switch from eucalypt pulp to bagasse pulp without sacrificing paper machine productivity. It is thought that two factors contributed to the high permeability of the bagasse pulp pad. Firstly, thicker cell walls of the bagasse pulp fibres resulted in high fibre stiffness. Secondly, the bagasse pulp had a large proportion of fibres longer than 1.3 mm. These attributes helped to reinforce the pulp pad matrix. The steady-state permeability and compressibility parameters for the eucalypt pulp were consistent with those found by previous workers. It was also found that Australian pulp derived from the ‘coarse’ bagasse fraction had higher steady-state permeability than the ‘medium’ fraction. However, there was no difference between bagasse pulp originating from a diffuser or a mill. The bagasse pre-treatment options investigated in this study were not found to affect the steady-state compressibility parameters of a pulp pad. The dynamic filtration model was found to give predictions that were in good agreement with experimental data for pads made from samples of pretreated bagasse pulp, provided at least some pith was removed prior to pulping. Applying vacuum to a pulp slurry in the modified DDJ dramatically reduced the drainage time. At any level of vacuum, bagasse pulp benefitted from chemical additives as quantified by reduced drainage time and increased retention of short fibres. Using the modified DDJ, it was observed that under specific conditions, a benchmark depithed bagasse pulp drained more rapidly than the ‘coarse’ bagasse pulp. In steady-state permeability and compressibility experiments, the addition of chemical additives improved the pad permeability and compressibility of a benchmark bagasse pulp with a high quantity of short fibres. Importantly, this effect was not observed for the ‘coarse’ bagasse pulp. However, dynamic filtration experiments showed that there was also a small observable improvement in filtration for the ‘medium’ bagasse pulp. The mechanism of bagasse pulp pad consolidation appears to be by fibre realignment. Chemical additives assist to lubricate the consolidation process. This study was complemented by pulp physical and chemical property testing and a microscopy study. In addition to its high pulp pad permeability, ‘coarse’ bagasse pulp often (but not always) had superior physical properties than a benchmark depithed bagasse pulp.

Experimental study of Australian sugarcane bagasse pulp permeability

In this experimental study the permeability of Australian bagasse chemical pulps obtained from different bagasse fractions were measured in a simple permeability cell and the results compared to one another as well as to eucalypt, Argentinean bagasse and pine pulps. The pulps were characterised in terms of the permeability parameters, the specific surface area, Sv, and the swelling factor, α. It was found that the bagasse fraction used affects these parameters. Fractionation of whole bagasse prior to pulping produced pulps that have permeability properties that compare favourably with eucalypt pulp. The values of Sv and α for bagasse pulp also depend on whether a constant or a variable Kozeny factor is used.

Volcanic stratigraphy, alteration zoning, and vein paragenesis of the Sascha-Pelligrini low-sulphidation epithermal system, Santa Cruz, Argentina

The Sascha-Pelligrini low-sulphidation epithermal system is located on the western edge of the Deseado Massif, Santa Cruz Province, Argentina. Outcrop sampling has returned values of up to 160g/t gold and 796g/t silver, with Mirasol Resources and Coeur D.Alene Mines currently exploring the property. Detailed mapping of the volcanic stratigraphy has defined three units that comprise the middle Jurassic Chon Aike Formation and two units that comprise the upper Jurassic La Matilde Formation. The Chon Aike Formation consists of rhyodacite ignimbrites and tuffs, with the La Matilde Formation including rhyolite ash and lithic tuffs. The volcanic sequence is intruded by a large flow-banded rhyolite dome, with small, spatially restricted granodiorite dykes and sills cropping out across the study area. ASTER multispectral mineral mapping, combined with PIMA (Portable Infrared Mineral Analyser) and XRD (X-ray diffraction) analysis defines an alteration pattern that zones from laumontite-montmorillonite, to illite-pyritechlorite, followed by a quartz-illite-smectite-pyrite-adularia vein selvage. Supergene kaolinite and steam-heated acid-sulphate kaolinite-alunite-opal alteration horizons crop out along the Sascha Vein trend and Pelligrini respectively. Paragenetically, epithermal veining varies from chalcedonic to saccharoidal with minor bladed textures, colloform/crustiform-banded with visible electrum and acanthite, crustiform-banded grey chalcedonic to jasperoidal with fine pyrite, and crystalline comb quartz. Geothermometry of mineralised veins constrains formation temperatures from 174.8 to 205.1¡ÆC and correlates with the stability field for the interstratified illite-smectite vein selvage. Vein morphology, mineralogy and associated alteration are controlled by host rock rheology, permeability, and depth of the palaeo-water table. Mineralisation within ginguro banded veins resulted from fluctuating fluid pH associated with selenide-rich magmatic pulses, pressure release boiling and wall-rock silicate buffering. The study of the Sascha-Pelligrini epithermal system will form the basis for a deposit-specific model helping to clarify the current understanding of epithermal deposits, and may serve as a template for exploration of similar epithermal deposits throughout Santa Cruz.

Mass transfer properties (permeability and mass diffusivity) of four australian hardwood species

Characterization of mass transfer properties was achieved in the longitudinal, radial, and tangential directions for four Australian hardwood species: spotted gum, blackbutt, jarrah, and messmate. Measurement of mass transfer properties for these species was necessary to complement current vacuum drying modeling research. Water-vapour diffusivity was determined in steady state using a specific vapometer. Permeability was determined using a specialized device developed to measure over a wide range of permeability values. Permeability values of some species and material directions were extremely low and undetectable by the mass flow meter device. Hence, a custom system based on volume evolution was conceived to determine very low, previously unpublished, wood permeability values. Mass diffusivity and permeability were lowest for spotted gum and highest for messmate. Except for messmate in the radial direction, the four species measured were less permeable in all directions than the lowest published figures, demonstrating the high impermeability of Australian hardwoods and partly accounting for their relatively slow drying rates. Permeability, water-vapour diffusivity, and associated anisotropic ratio data obtained for messmate were extreme or did not follow typical trends and is consequently the most difficult of the four woods to dry in terms of collapse and checking degradation. © The State of Queensland, Department of Agriculture, Fisheries and Forestry, 2012.

Permeability estimation conditioned to geophysical downhole log data in sandstones of the northern Galilee Basin, Queensland : methods and application

This study uses borehole geophysical log data of sonic velocity and electrical resistivity to estimate permeability in sandstones in the northern Galilee Basin, Queensland. The prior estimates of permeability are calculated according to the deterministic log–log linear empirical correlations between electrical resistivity and measured permeability. Both negative and positive relationships are influenced by the clay content. The prior estimates of permeability are updated in a Bayesian framework for three boreholes using both the cokriging (CK) method and a normal linear regression (NLR) approach to infer the likelihood function. The results show that the mean permeability estimated from the CK-based Bayesian method is in better agreement with the measured permeability when a fairly apparent linear relationship exists between the logarithm of permeability and sonic velocity. In contrast, the NLR-based Bayesian approach gives better estimates of permeability for boreholes where no linear relationship exists between logarithm permeability and sonic velocity.

Improved estimates of percolation and anisotropic permeability from 3-D X-ray microtomography using stochastic analyses and visualization

X-ray microtomography (micro-CT) with micron resolution enables new ways of characterizing microstructures and opens pathways for forward calculations of multiscale rock properties. A quantitative characterization of the microstructure is the first step in this challenge. We developed a new approach to extract scale-dependent characteristics of porosity, percolation, and anisotropic permeability from 3-D microstructural models of rocks. The Hoshen-Kopelman algorithm of percolation theory is employed for a standard percolation analysis. The anisotropy of permeability is calculated by means of the star volume distribution approach. The local porosity distribution and local percolation probability are obtained by using the local porosity theory. Additionally, the local anisotropy distribution is defined and analyzed through two empirical probability density functions, the isotropy index and the elongation index. For such a high-resolution data set, the typical data sizes of the CT images are on the order of gigabytes to tens of gigabytes; thus an extremely large number of calculations are required. To resolve this large memory problem parallelization in OpenMP was used to optimally harness the shared memory infrastructure on cache coherent Non-Uniform Memory Access architecture machines such as the iVEC SGI Altix 3700Bx2 Supercomputer. We see adequate visualization of the results as an important element in this first pioneering study.

Water absorption, permeability, and resistance to chloride-ion penetration of lightweight aggregate concrete

This paper presents an experimental study to evaluate effect of cumulative lightweight aggregate (LWA) content (including lightweight sand) in concrete [water/cement ratio (w/c) = 0.38] on its water absorption, water permeability, and resistance to chloride-ion penetration. Rapid chloride penetrability test (ASTM C 1202), rapid migration test (NT Build 492), and salt ponding test (AASHTO T 259) were conducted to evaluate the concrete resistance to chloride-ion penetration. The results were compared with those of a cement paste and a control normal weight aggregate concrete (NWAC) with the same w/c and a NWAC (w/c = 0.54) with 28-day compressive strength similar to some of the lightweight aggregate concrete (LWAC). Results indicate that although the total charge passed, migration coefficient, and diffusion coefficient of the LWAC were not significantly different from those of NWAC with the same w/c of 0.38, resistance of the LWAC to chloride penetration decreased with increase in the cumulative LWA content in the concretes. The water penetration depth under pressure and water sorptivity showed, in general, similar trends. The LWAC with only coarse LWA had similar water sorptivity, water permeability coefficient, and resistance to chloride-ion penetration compared to NWAC with similar w/c. The LWAC had lower water sorptivity, water permeability and higher resistance to chloride-ion penetration than the NWAC with similar 28-day strength but higher w/c. Both the NWAC and LWAC had lower sorptivity and higher resistance to chloride-ion penetration than the cement paste with similar w/c.

Permeability of high-performance concrete incorporating presoaked lightweight aggregates for internal curing

This paper presents an experimental study on the effect of presoaked lightweight aggregates (LWAs) for internal curing on water permeability, water absorption and resistance of concrete to chloride-ion penetration in comparison with those of a control concrete and a concrete with shrinkage reducing admixture (SRA) of similar water/cement ratios (w/c). In general, the concretes with LWA particles had initial water absorption, sorptivity and water permeability similar to or lower than those of the control concrete and the concrete with SRA. The charges passed, chloride migration coefficient and chloride diffusion coefficient of such concretes were in the same order as those of the control concrete and the concrete with SRA. However, the incorporation of the LWAs for internal curing reduced unit weight, compressive strength and elastic modulus of the concrete. Comparing the LWAs of different sizes for internal curing, finer particles were more efficient in reducing the shrinkage and generally resulted in less reduction in the unit weight, compressive strength, and elastic modulus. However, the increase in the more porous crushed LW particles in concrete seems to increase the penetration of chloride ions in the concrete. The concrete with SRA had initial water absorption, sorptivity, water permeability and resistance to chloride ion penetration comparable with those of the control concrete. The use of SRA in concrete does not affect the elastic modulus of the concrete, except for a minor influence on the compressive strength of the concrete.

Effect of reactive bed mineralogy on arsenic retention and permeability of synthetic arsenic-containing acid mine drainage

Successive alkalinity producing systems (SAPSs) are widely used for treating acid mine drainage (AMD) and alleviating clogging commonly occurring in limestone systems due to an amorphous ferric precipitate. In this study, iron dust, bone char, micrite and their admixtures were used to treat arseniccontaining AMD. A particular interest was devoted to arsenic removal performance, mineralogical constraints on arsenic retention ability and permeability variation during column experiment for 140 days. The results showed that the sequence of the arsenic removal capacity was as follows: bone char > micrite > iron dust. The combination of 20% v/v iron dust and 80% v/v bone char/micrite columns can achieve better hydraulic conductivity and phosphorus-retention capacity than single micrite and bone char columns. The addition of iron dust created reductive environment and resulted in the transformation of coating material from colloidal phase to secondary mineral phase, such as green rust and phosphoerrite, which obviously ameliorates hydraulic conductivity of systems. The sequential extraction experiments indicated that the stable fractions of arsenic in columns were enhanced with help of iron dust compared to single bone char and micrite columns. A combination of iron dust and micrite/bone char represented a potential SAPS for treating As-containing AMD.

Dynamic effects of electrical pitting in steam-turbine tilting-pad thrust-bearings

This paper merges the analysis of a case history and the simplified theoretical model related to a rather singular phenomenon that may happen in rotating machinery. Starting from the first, a small industrial steam turbine experienced a very strange behavior during megawatt load. When the unit was approaching the maximum allowed power, the temperature of the babbitt metal of the pads of the thrust bearing showed constant increase with an unrecoverable drift. Bearing inspection showed that pad trailing edge had the typical aspect of electrical pitting. This kind of damage was not reparable and bearing pads had to replaced. This problem occurred several times in sequence and was solved only by adding further ground brushes to the shaft-line. Failure analysis indicated electrodischarge machining as the root fault. A specific model, able to take into consideration the effect of electrical pitting and loading capacity decreasing as a consequence of the damage of the babbitt metal, is proposed in the paper and shows that the phenomenon causes the irretrievable failure of the thrust bearing.