Kinetic Assessment of Kraft and Thermally Upgraded Kraft Papers Aged in Five Alternative Dielectric Fluids.

The lifespan of an electrical transformer, primarily determined by the condition of its solid insulation, is well known under various operating conditions when mineral oil is the coolant in these machines. However, there is a trend toward replacing this oil with biodegradable fluids, especially esters; therefore, an understanding of the ageing of solid insulation with these fluids is essential. Currently available data do not allow for the selection of the best ester among those available on the market, as each study applies different conditions, making it impossible to compare results. Thus, this paper analyses the degradation of Kraft and Thermally Upgraded Kraft papers with the following five most promising commercial esters: sunflower, rapeseed, soybean, palm, and synthetic. The materials underwent accelerated thermal ageing at 130, 150, and 170 °C, and the integrity of the papers was evaluated through their polymerisation degree and the obtaining of the degradation kinetic models. The wide range of materials studied in this work, which were subjected to the same treatments, allows for a comparison of the esters, revealing significant differences in the impact of the alternative fluids. Sunflower, rapeseed, and soybean esters provided the best paper protection, i.e., the degree of polymerisation of Kraft paper in the tests at 150 °C decreased by 71% with these fluids, compared to the 83% reduction with mineral oil, 79% reduction with palm ester, and 75% reduction with synthetic ester. Furthermore, different kinetic models were obtained to predict the degradation; it was concluded that the Emsley model provides the best fit. Additionally, it was found that the behaviour of a dielectric fluid with one type of paper cannot be extrapolated, which is only noticeable in broad-scope studies.

Corrigendum to "Experimental dataset on the compressive mechanical properties of high-density pressboard used in power transformers spacers" [Data in Brief 50 (2023) 109471].

[This corrects the article DOI: 10.1016/j.dib.2023.109471.].

Experimental dataset on the compressive mechanical properties of high-density pressboard used in power transformers spacers.

The structural elements within power transformers are commonly constructed from high-density pressboard, chosen for its favourable mechanical and dielectric properties. Among these elements are the spacers employed in the windings of transformers, which endure compressive loading during operation. The spacers are immersed in dielectric fluid and exposed to high temperatures and chemical reactions over the transformer's lifespan, resulting in the degradation of their dielectric and mechanical properties. The mechanical integrity of the power transformer significantly relies on these factors; hence, it is imperative to comprehend how ageing deteriorates the mechanical response of the high-density pressboard. The present article presents experimental data on the compressive mechanical properties of a commercially available high-density pressboard, commonly employed in power transformer spacers, under various ageing conditions (induced through accelerated thermal ageing and assessed by the degree of polymerisation). These data hold potential for diverse applications. They can enhance the existing comprehension of the mechanical behaviour and degradation mechanisms of cellulosic insulation in power transformers and provide reference benchmarks for comparison with factory-obtained values by manufacturers. In the realm of engineering failure analysis, these values can be utilised to evaluate the mechanical failures of paper-based materials utilised as structural components in power transformers.

Resistance of Ion Exchange Membranes in Aqueous Mixtures of Monovalent and Divalent Ions and the Effect on Reverse Electrodialysis.

Salinity gradient energy has gained attention in recent years as a renewable energy source, especially employing reverse electrodialysis technology (RED), which is based on the role of ion exchange membranes. In this context, many efforts have been developed by researchers from all over the world to advance the knowledge of this green source of energy. However, the influence of divalent ions on the performance of the technology has not been deeply studied. Basically, divalent ions are responsible for an increased membrane resistance and, therefore, for a decrease in voltage. This work focuses on the estimation of the resistance of the RED membrane working with water flows containing divalent ions, both theoretically by combining the one-thread model with the Donnan exclusion theory for the gel phase, as well as the experimental evaluation with Fumatech membranes FAS-50, FKS-50, FAS-PET-75, and FKS-PET-75. Furthermore, simulated results have been compared to data recently reported with different membranes. Besides, the influence of membrane resistance on the overall performance of reverse electrodialysis technology is evaluated to understand the impact of divalent ions in energy generation. Results reflect a minor effect of sulfate on the gross power in comparison to the effect of calcium and magnesium ions. Thus, this work takes a step forward in the knowledge of reverse electrodialysis technology and the extraction of salinity gradient energy by advancing the influence of divalent ions on energy recovery.

Thin-Film Composite Matrimid-Based Hollow Fiber Membranes for Oxygen/Nitrogen Separation by Gas Permeation.

In recent years, the need to reduce energy consumption worldwide to move towards sustainable development has led many of the conventional technologies used in the industry to evolve or to be replaced by new alternatives. Oxygen is a compound with diverse industrial and medical applications. For this reason, obtaining it from air is one of the most interesting separations, traditionally performed by cryogenic distillation and pressure swing adsorption, two techniques which are very energetically expensive. In this sense, the implementation of membranes in a hollow fiber configuration is presented as a much more efficient alternative to carry out this separation. The aim of this work is to develop cost-effective multilayer hollow fiber composite membranes made of Matrimid and polydimethylsiloxane (PDMS) for the separation of oxygen and nitrogen from air. PDMS is used as a cover layer but can also enhance the performance of the membrane. In order to compare these two materials, three different configurations are studied. First, integral asymmetric Matrimid hollow fiber membranes were produced using the spinning method. Secondly, by using dip-coating method, a PDMS dense selective layer was deposited on a self-made polyvinylidene fluoride (PVDF) hollow fiber support. Finally, the performance of a dual-layer hollow fiber membrane of Matrimid and PDMS was studied. Membrane morphology was characterized by SEM and separation performance of the membranes was evaluated by mixed-gas permeation experiments. The novelty presented in this work is the manufacture of hollow fiber membranes and the way Matrimid is treated. This makes it possible to develop much thinner dense layers than in the case of flat-sheet membranes, which leads to higher permeance values. This is a key factor when implementing this technology on an industrial scale. Membranes prepared in this work were compared to the current state of the art, reporting quite good performance for the dual-layer membrane, reaching O2 permeance of 30.8 GPU and O2/N2 selectivity of 4.7, with a thickness of about 5-10 µm (counting both selective layers). In addition, the effect of operating temperature on the membrane permeances has been studied experimentally; we analyze its influence on the selectivity of the separation process.

PEBA/PDMS Composite Multilayer Hollow Fiber Membranes for the Selective Separation of Butanol by Pervaporation.

The growing interest in the production of biofuels has motivated numerous studies on separation techniques that allow the separation/concentration of organics produced by fermentation, improving productivity and performance. In this work, the preparation and characterization of new butanol-selective membranes was reported. The prepared membranes had a hollow fiber configuration and consisted of two dense selective layers: a first layer of PEBA and a second (outer) layer of PDMS. The membranes were tested to evaluate their separation performance in the selective removal of organics from a synthetic ABE solution. Membranes with various thicknesses were prepared in order to evaluate the effect of the PDMS protective layer on permeant fluxes and membrane selectivity. The mass transport phenomena in the pervaporation process were characterized using a resistances-in-series model. The experimental results showed that PEBA as the material of the dense separating layer is the most favorable in terms of selectivity towards butanol with respect to the other components of the feed stream. The addition of a protective layer of PDMS allows the sealing of possible pinholes; however, its thickness should be kept as small as possible since permeation fluxes decrease with increasing thickness of PDMS and this material also has greater selectivity towards acetone compared to other feed components.

Antibacterial peptide fractions from chia seeds (Salvia hispanica L.) and their stability to food processing conditions.

Foodborne pathogens are one of the major causes of food deterioration and a public health concern worldwide. Antimicrobial peptides (AMPs) encrypted in protein sequences from plants, such as chia (Salvia hispanica), might have a crucial role in the inhibition of bacteria. In this study, the antibacterial activity and stability of chia peptide fractions (CPFs) were evaluated for potential applications in food preservation. Three CPFs (F < 1, F 1-3, and F 3-5 kDa) were obtained by enzymatic hydrolysis of a protein-rich fraction and subsequent ultrafiltration. Gram-positive bacteria were susceptible to F < 1. This fraction's more significant inhibition effect was reported against Listeria monocytogenes (635.4 ± 3.6 µg/mL). F < 1 remained active after incubation at 4-80 °C and a pH range of 5-8 but was inactive after exposure to pepsin and trypsin. In this sense, F < 1 could be suitable for meat and dairy products at a maximum reference level of 12-25 mg/kg. Multicriteria analysis suggested that KLKKNL could be the peptide displaying the antimicrobial activity in F < 1. These results demonstrate the potential of this sequence as a preservative for controlling the proliferation of Gram-positive bacteria in food products.

Mineral and Ester Nanofluids as Dielectric Cooling Liquid for Power Transformers.

Amidst the new techniques facing the improvement of cooling and insulating efficiency and the design of electric transformers, constrained by the current technologies, one of the more promising is the substitution of traditional dielectric oils for nanofluids. Research on nanofluids for their application in transformers as a coolant and dielectric medium have been performed during the last two decades and continue today. This review tries to collect and analyze the available information in this field and to offer it already dissected to researchers, focusing on the preparation methods and how nanoparticles affect the main properties of the base fluids. Here we also addressed the influence of different parameters as particle characteristics or environmental conditions in nanofluids performance, the evolution with time of the measured properties, or the neighboring relationship of nanofluids with other transformer components. In this sense, the most reviewed articles reflect enhancements of thermal conductivity or dielectric strength, as well as an improvement of time evolution of these properties, with respect to those that are found in base fluids, and, also, a better interaction between these nanofluids and dielectric cellulosics. Thus, the use of dielectric nanofluids in transformers may allow these machines to work safer or over their design parameters, reducing the risk of failure of the electrical networks and enhancing their life expectancy. Nevertheless, these advantages will not be useful unless a proper stability of nanofluids is ensured, which is achieved in a small part of revised articles. A compendium of the preparation methodology with this aim is proposed, to be checked in future works.

Hydrogen Recovery from Coke Oven Gas. Comparative Analysis of Technical Alternatives.

The recovery of energy and valuable compounds from exhaust gases in the iron and steel industry deserves special attention due to the large power consumption and CO2 emissions of the sector. In this sense, the hydrogen content of coke oven gas (COG) has positioned it as a promising source toward a hydrogen-based economy which could lead to economic and environmental benefits in the iron and steel industry. COG is presently used for heating purposes in coke batteries or furnaces, while in high production rate periods, surplus COG is burnt in flares and discharged into the atmosphere. Thus, the recovery of the valuable compounds of surplus COG, with a special focus on hydrogen, will increase the efficiency in the iron and steel industry compared to the conventional thermal use of COG. Different routes have been explored for the recovery of hydrogen from COG so far: i) separation/purification processes with pressure swing adsorption or membrane technology, ii) conversion routes that provide additional hydrogen from the chemical transformation of the methane contained in COG, and iii) direct use of COG as fuel for internal combustion engines or gas turbines with the aim of power generation. In this study, the strengths and bottlenecks of the main hydrogen recovery routes from COG are reviewed and discussed.

Environmental sustainability of alternative marine propulsion technologies powered by hydrogen - a life cycle assessment approach.

Shipping is a very important source of pollution worldwide. In recent years, numerous actions and measures have been developed trying to reduce the levels of greenhouse gases (GHG) from the marine exhaust emissions in the fight against climate change, boosting the Sustainable Development Goal 13. Following this target, the action of hydrogen as energy vector makes it a suitable alternative to be used as fuel, constituting a very promising energy carrier for energy transition and decarbonization in maritime transport. The objective of this study is to develop an ex-ante environmental evaluation of two promising technologies for vessels propulsion, a H2 Polymeric Electrolytic Membrane Fuel Cell (PEMFC), and a H2 Internal Combustion Engine (ICE), in order to determine their viability and eligibility compared to the traditional one, a diesel ICE. The applied methodology follows the Life Cycle Assessment (LCA) guidelines, considering a functional unit of 1 kWh of energy produced. LCA results reveal that both alternatives have great potential to promote the energy transition, particularly the H2 ICE. However, as technologies readiness level is quite low, it was concluded that the assessment has been conducted at a very early stage, so their sustainability and environmental performance may change as they become more widely developed and deployed, which can be only achieved with political and stakeholder's involvement and collaboration.

Kinetic Assessment of Mechanical Properties of a Cellulose Board Aged in Mineral Oil and Synthetic Ester.

In oil-immersed power transformers, the insulation system is constituted of a dielectric oil-solid combination. The insulation oil generally used is mineral oil; however, this fluid has started to be substituted by natural and synthetic esters due to their higher biodegradability and flash point. The introduction of a new fluid in the insulation system of power transformers requires kinetic models that can estimate the degradation rate of insulation solids. The aim of this work was to go further in quantifying through different kinetic models the deterioration suffered by a commercial cellulose board (PSP 3055), which is one of the solid materials used in the insulation system of oil-filled transformers. The aging study was extended to cellulose board specimens immersed in two different oils (mineral and synthetic ester). It was obtained that there is a lower degradation when synthetic ester is used in the insulation system. Additionally, it can be concluded that the use of mechanical properties to quantify the degradation of the cellulose board through kinetic models provides information about the different behavior shown by PSP 3055 when different fiber direction angles are considered.

Experimental dataset on the tensile and compressive mechanical properties of plain Kraft and crepe papers used as insulation in power transformers after ageing in mineral oil.

The solid insulation in the windings of power transformers, which generally consists of oil-impregnated thin paper, is one of the key elements for the performance and durability of these electrical machines. Insulation paper is subjected to static and dynamic forces of electromagnetic origin, in combination with high temperatures and chemical reactions, during the operating life of a power transformer. The mechanical properties of the cellulosic insulation are relevant parameters because its breakage could result in the electric failure of the transformer. Indeed, paper manufacturers usually provide values of the tensile strength and elongation at breakage of the insulating paper in its two principal material directions, the MD (machine direction) and CD (cross-direction). However, paper is a highly anisotropic material and its material properties evolve as the paper insulation ages. The paper insulation in an operating transformer is subjected to a multiaxial stress state field including compressive and shear stresses. This article reports experimental data on the tensile and compressive mechanical properties of two types of paper, plain Kraft and crepe paper, typically used as insulation in power transformers, under different ageing states (which were induced through accelerated thermal ageing and quantified by means of the degree of polymerisation). These data could be reused for several purposes. They can improve the current understanding of the mechanical response and degradation processes of the cellulosic insulation in power transformers, and give some reference values that can be compared with others obtained in the factory by manufacturers. In the field of engineering failure analysis, those values could be reused for the assessment of mechanical failure of paper materials used in power transformers, see [1].

Exploring the Potential Application of Matrimid® and ZIFs-Based Membranes for Hydrogen Recovery: A Review.

Hydrogen recovery is at the center of the energy transition guidelines promoted by governments, owing to its applicability as an energy resource, but calls for energetically nonintensive recovery methods. The employment of polymeric membranes in selective gas separations has arisen as a potential alternative, as its established commercial availability demonstrates. However, enhanced features need to be developed to achieve adequate mechanical properties and the membrane performance that allows the obtention of hydrogen with the required industrial purity. Matrimid®, as a polyimide, is an attractive material providing relatively good performance to selectively recover hydrogen. As a consequence, this review aims to study and summarize the main results, mechanisms involved and advances in the use of Matrimid® as a selective material for hydrogen separation to date, delving into membrane fabrication procedures that increase the effectiveness of hydrogen recovery, i.e., the addition of fillers (within which ZIFs have acquired extraordinary importance), chemical crosslinking or polymeric blending, among others.

Titania Nanofluids Based on Natural Ester: Cooling and Insulation Properties Assessment.

The assessment of a TiO2 vegetal-based dielectric nanofluid has been carried out, and its characteristics and behavior have been tested and compared with a previously tested maghemite nanofluid. The results obtained reflect a similar affectation of the main properties, with a maximal improvement of the breakdown voltage of 33% at 0.5 kg/m3, keeping the thermal conductivity and the viscosity almost constant, especially the first one. This thermal characterization agrees with the results obtained when applying the TiO2 optimal nanofluid in the cooling of an experimental setup, with a slightly worse performance than the base fluid. Nevertheless, this performance is the opposite to that noticed with the ferrofluid, which was capable of improving the cooling of the transformer and decreasing its temperature. The similarities between the characterizations of both nanofluids, the differences in their cooling performances and their different magnetic natures seem to point out the presence of additional thermomagnetic buoyancy forces to support the improvement of the cooling.

Effect of TiO2 and ZnO Nanoparticles on the Performance of Dielectric Nanofluids Based on Vegetable Esters During Their Aging.

Over the last few decades the insulating performance of transformer oils has been broadly studied under the point of view of nanotechnology, which tries to improve the insulating and heat dissipation performance of transformer oils by suspending nanoparticles. Many authors have analyzed the thermal and dielectric behavior of vegetable oil based-nanofluids, however, very few works have studied the evolution of these liquids during thermal aging and their stability. In this paper has been evaluated the performance of aged vegetable oil based-nanofluids, which have been subjected to accelerated thermal aging at 150 °C. Nanoparticles of TiO2 and ZnO have been dispersed in a commercial natural ester. Breakdown voltage, resistivity, dissipation factor and acidity of nanofluid samples have been measured according to standard methods, as well as stability. Moreover, it has been analyzed the degradation of Kraft paper through the degree of polymerization (DP). The results have showed that although nanoparticles improve breakdown voltage, they increase the ageing of insulation liquids and dielectric paper.

Plataforma para el registro de nefrolitotomía percutánea interinstitucional / Platform for the registration of inter-institutional percutaneous nephrolithotomy

Desde la primera introducción de la nefrolitotomía percutánea (NLP) por Fernstrom y su popularización en EE. UU. por Smith, la NLP se ha convertido en el estándar de oro para pacientes con cálculos renales de gran tamaño.1 Las opciones actuales para el tratamiento de cálculos renales son: la litotripcia extracorpórea, la ureterorrenoscopia flexible y la NLP, escogiendo cada una según el tamaño del cálculo, la anatomía del sistema colector, las características del paciente y las preferencias del especialista.2 Para cálculos piélicos o de cáliz superior mayores de 2 cm o para cáliz inferior mayores de 1,5 cm, se prefiere la NLP.2

Since the first introduction of percutaneous nephrolithotomy (PNL) by Fernstrom and its popularization in the US by Smith, PNL has become the gold standard for patients with large kidney stones.1 Current options for the treatment of kidney stones include extracorporeal lithotripsy, flexible ureterorenoscopy, and PNL, each chosen according to the size of the stone, the anatomy of the collecting system, the patient's characteristics, and the specialist's preferences.2 For upper calyx or skin stones larger than 2 cm or for lower calyx larger than 1.5 cm, PNL is preferred.2

Hand hygiene technique quality evaluation in nursing and medicine students of two academic courses.

OBJECTIVE: because they are health professionals, nursing and medical students' hands during internships can function as a transmission vehicle for hospital-acquired infections. METHOD: a descriptive study with nursing and medical degree students on the quality of the hand hygiene technique, which was assessed via a visual test using a hydroalcoholic solution marked with fluorescence and an ultraviolet lamp. RESULTS: 546 students were assessed, 73.8% from medicine and 26.2% from nursing. The area of the hand with a proper antiseptic distribution was the palm (92.9%); areas not properly scrubbed were the thumbs (55.1%). 24.7% was very good in both hands, 29.8% was good, 25.1% was fair, and 20.3% was poor. The worst assessed were the male, nursing and first year students. There were no significant differences in the age groups. CONCLUSIONS: hand hygiene technique is not applied efficiently. Education plays a key role in setting a good practice base in hand hygiene, theoretical knowledge, and in skill development, as well as good practice reinforcement.

Hand hygiene assessment in the workplace using a UV lamp.

The aim of this study was to determine the quality of the hand hygiene (HH) technique of healthcare workers (HCW) in real conditions, without previous education or training. All 705 participants did the World Health Organization sequence for HH correctly, but only 9.5% actually achieved the highest rating (ie, all hand areas with hand rub distribution).

Hand hygiene technique quality evaluation in nursing and medicine students of two academic courses / Avaliação da qualidade da técnica de higiene das mãos em alunos de enfermagem e medicina em dois cursos de graduação / Evaluación de la calidad de la técnica de higiene de manos en alumnos de enfermería y medicina en dos cursos académicos

AbstractObjective: because they are health professionals, nursing and medical students' hands during internships can function as a transmission vehicle for hospital-acquired infections.Method: a descriptive study with nursing and medical degree students on the quality of the hand hygiene technique, which was assessed via a visual test using a hydroalcoholic solution marked with fluorescence and an ultraviolet lamp.Results: 546 students were assessed, 73.8% from medicine and 26.2% from nursing. The area of the hand with a proper antiseptic distribution was the palm (92.9%); areas not properly scrubbed were the thumbs (55.1%). 24.7% was very good in both hands, 29.8% was good, 25.1% was fair, and 20.3% was poor. The worst assessed were the male, nursing and first year students. There were no significant differences in the age groups.Conclusions: hand hygiene technique is not applied efficiently. Education plays a key role in setting a good practice base in hand hygiene, theoretical knowledge, and in skill development, as well as good practice reinforcement.

ResumoObjetivo:assim como as mãos dos professionais de saúde, as mãos dos estudantes de Enfermagem e Medicina durante os estágios clínicos podem funcionar como veículo de transmissão das infecções hospitalares.Método:estudo descritivo com estudantes de Graduação em Enfermagem e Medicina. Avaliou-se a qualidade da técnica de higiene das mãos por meio de prova visual a partir de solução hidro-alcoólica marcada com fluoresceína e lâmpada de luz ultravioleta.Resultados:avaliaram-se 546 alunos, 73,8% da Graduação em Medicina e 26,2% da Enfermagem. As áreas das mãos com correta distribuição de sabão foram as palmas (92,9%); as áreas não esfregadas corretamente foram os polegares (55,1%). Em ambas as mãos, a higienização foi muito boa em 24,7%, boa em 29,8%, regular em 25,1% e má em 20,3%. Os piores foram: os homens, os estudantes de Enfermagem e os estudantes do primeiro ano de escola. Não houve diferenças significativas por idade.Conclusões:a técnica de higiene de mãos não foi realizada de modo eficaz. O papel educativo é fundamental para sedimentar as bases de boas práticas na higienização das mãos, em conhecimentos teóricos e no desenvolvimento de habilidades e reforço de boas práticas.

ResumenObjetivo:al igual que los profesionales sanitarios, las manos de los estudiantes de enfermería y medicina durante las estancias clínicas pueden funcionar como vehículo de trasmisión de las infecciones nosocomiales.Método:estudio descriptivo con estudiantes de Grado de Enfermería y de Medicina. Se evaluó la calidad de la técnica de la higiene de manos por prueba visual con solución hidroalcohólica marcada con fluoresceína y lámpara de luz ultravioleta.Resultados:se evaluó a 546 alumnos, Grado de Medicina 73,8% y 26,2% de Enfermería. Las zonas de las manos con una correcta distribución de desinfectante fueron las palmas (92,9%); las no frotadas correctamente fueron los pulgares (55,1%). En ambas manos fue muy buena en el 24,7%, buena en el 29,8%, regular en 25,1% y mala en 20,3%. Los peores han sido: los hombres, los estudiantes de enfermería y los de primer año de estudio. No hubo diferencias significativas por edad.Conclusiones:no se realizó la técnica de higiene de manos de una manera eficaz. El papel de la educación es fundamental para sentar las bases de buenas prácticas en higiene de manos, en conocimientos teóricos y en el desarrollo de habilidades y el refuerzo de buenas prácticas.

Necrobiosis lipoídica: reporte de un caso / Necrobiosis lipoidica: a case report

Presentamos un paciente femenino con necrobiosis lipoídica no relacionada a diabetes mellitus. Los mecanismos etiopatogénicos son aún poco entendidos y la respuesta a las diversas modalidades de tratamiento es inconstante