Monitoring insulator contamination level under dry condition with a microwave reflectometer

—Build-up of surface contamination on high voltage insulators can lead to an increase in leakage current and partial discharge, which may eventually develop into flashover. Conventional contamination level monitoring systems based on leakage current, partial discharge, infrared and ultraviolet camera are only effective when the contamination layer has been wetted by rain, fog or condensation; under these conditions flashover might occur before there is time to implement remedial measures such as cleaning. This paper describes studies exploring the feasibility of applying microwave reflectometry techniques to monitor insulator contamination levels. This novel method measures the power generated by a 10.45 GHz source and reflected at the insulator contamination layer. A theoretical model establishes the relationship between equivalent salt deposit density (ESDD) levels, dielectric properties and geometry of contamination layers. Experimental results demonstrate that the output from the reflectometer is able to clearly distinguish between samples with different contamination levels under dry conditions. This contamination monitoring method could potentially provide advance warning of the future failure of wet insulators in climates where insulators can experience dry conditions for extended periods

Mode I Delamination Fracture Characterization of Polymeric Composites under Elevated Temperature

Delamination is one of the major failure modes seen in the laminated polymeric matrix composite (PMC). Accurate prediction of delamination initiation and propagation is important for the design and analysis of robust composite structures. Existing experimental methodologies that are based on linear elastic fracture mechanics are inadequate to characterize delamination fracture properties under elevated temperature when PMC properties become time-, loading-history, and rate-dependent. A new experimental methodology based on linear viscoelastic fracture theory is developed and verified through finite element analysis and experiments. This new technique determines crack growth curves, such as stress intensity factor vs. crack growth speed and fracture initiation energy vs. crack initiation time, through the experimentally determined J-integral, Js, for a linear viscoelastic double cantilever beam (DCB) specimen. Special test setup is designed and validated for determining accurate Js using just the applied load and the load end rotation angles. This new methodology is then applied to measure the mode I fracture properties of a highly toughened graphite/epoxy composite under various environmental conditions

Moisture ingress in photovoltaic modules: A review

Moisture ingress in photovoltaic (PV) modules is the core of most degradation mechanisms that lead to PV module power degradation. Moisture in EVA encapsulant can lead to metal grids corrosion, delamination and discolouration of encapsulants, potential induced degradation, optical and adhesion losses. The present work is a review of literature on the causes, effects, detection, and mitigation techniques of moisture ingress in PV modules. Literature highlights on determining the diffusivity, solubility, and permeability of polymeric components of PV modules via water vapour transmission rate tests, gravimetric, and immersion methods, have been presented. Electroluminescence, photoluminescence, and ultraviolet fluorescence spectroscopy, as well as dark lock-in thermography are some techniques used to detect moisture ingress in modules. Encapsulants with excellent moisture barrier and adhesion characteristics, desiccant-stacked polyisobutylene sealants, imbedded moisture sensors, and PV designs with/without breathable backsheets are ways of preventing/detecting moisture ingression in PV modules. Areas of focus for future research activities have also been discussed.publishedVersio

Modifying Inhibited Primer Performance via Control of Epoxy-Amine Matrix Structure and Composition

This research represents an effort to deliver a new fundamental understanding of how polymer matrix characteristics influence corrosion protection of organic coatings, in particular the performance of corrosion inhibitor-containing primers. By modifying the structure and composition features of epoxy-amine matrices which commonly serves as the binder for protective coatings, the thermal/mechanical, adhesion, and transport properties which govern coating performance and inhibitor release were altered in such a way that directly influenced protection efficacy. This research is composed of three distinct approaches towards systematically varying thermoset network characteristics and observing the resulting impact on transport behaviors and corrosion prevention, with an ultimate goal of understanding what may be tuned to provide improved protection from chromate replacement inhibitor pigments (CRIs). In the first network series, free volume properties and water sorption values served as the primary polymeric characteristics monitored with respect to differing relative humidity environments while trends in moisture transport were observed and quantified. Experimental observations of thermomechanical properties and oxygen permeation following water sorption were related to polymer void size and environmental severity conditions with clear distinctions relative to polymer swelling processes. The second research approach focused on a matrix series with incremental shifts in crosslink density, glass transition temperature, and hydrophilic monomer concentration while the degree to which these characteristics influenced water sorption and hydroplasticization were monitored and, in turn, modified the matrix swelling characteristics and corrosion protection efficiency with either chromate or chromate-free corrosion inhibitors. The third and final research section revolved around a network series formulated to effect varying matrix hydrophilicity while maintaining a minimal variance in raw materials and a static network architecture. Moisture transport properties were related with corrosion protection while quantifying inhibitor depletion under accelerated corrosion tests using Raman microscopy. The findings of these varied approaches were combined and compared to produce a more comprehensive description of water and inhibitor transport in epoxy-amine matrices and to directly interrogate the performance criteria that increase CRI performance in organic protective coatings

Porous materials in building energy technologies—a review of the applications, modelling and experiments

Improving energy efficiency in buildings is central to achieving the goals set by Paris agreement in 2015, as it reduces the energy consumption and consequently the emission of greenhouse gases without jeopardising human comfort. The literature includes a large number of articles on energy performance of the residential and commercial buildings. Many researchers have examined porous materials as affordable and promising means of improving the energy efficiency of buildings. Further, some of the natural media involved in building energy technologies are porous. However, currently, there is no review article exclusively focused on the porous media pertinent to the building energy technologies. Accordingly, this article performs a review of literature on the applications, modelling and experimental studies about the materials containing macro, micro, and nano-porous media and their advantages and limitations in different building energy technologies. These include roof cooling, ground-source heat pumps and heat exchangers, insulations, and thermal energy storage systems. The progress made and the remaining challenges in each technology are discussed and some conclusions and suggestions are made for the future research

Innovative approach to use guayule resin as a bio-based asphalt alternative

Asphalt cement will not last long as the world encounters a diminishment in crude oil. Novel resources can contribute to replacing asphalt with the sustainable, flexible pavement. This study presented guayule resin (guayule) as an innovative bio-based asphalt alternative. Ground tire rubber was used as an asphalt enhancer. To judge the guayule\u27s contribution, guayule-based binders were investigated and compared to control asphalt and asphalt-rubber binders. Binders were assessed according to comprehensive Superpave criteria and advanced rheological tests. Component analysis was performed to link the microscale level with the macroscale level. To validate the novel binder, satisfying mix performance tests were conducted. The outcomes revealed a lower viscosity for guayule than asphalt, indicating savings in plant energy consumption. Guayule had similarities with asphalt in component composition and rheological behavior with temperature susceptibility. Asphalt-guayule interaction yielded a physical blending with no chemical reaction. Rubber enhanced guayule at high temperatures, but not as much as asphalt, as proven by polymeric component migration through liquid binder due to depolymerization occurred. However, because of strong oxidation bonding chains attributed to guayule, the oxidative aging negatively affected the guayule-based binder’s long-term distresses. Validation by mix performance assessment revealed that guayule supported mix stability against moisture (particularly at lower air contents), rutting, and fatigue cracking, but had low thermal fracture resistance. In a nutshell, guayule had potential to replace conventional asphalt to compensate or surpass the asphalt performance required partially or even entirely at specific grades --Abstract, page iii

Far-infrared study of the Jahn-Teller distorted C60 monoanion in C60 tetraphenylphosphoniumiodide

We report high-resolution far-infrared transmission measurements on C(60)-tetraphenylphosphoniumiodide as a function of temperature. In the spectral region investigated (20-650 cm(-1)), we assign intramolecular modes of the C(60) monoanion and identify low-frequency combination modes. The well-known F(1u)(1) and F(1u)(2) modes are split into doublers at room temperature, indicating a D(5d) or D(3d) distorted ball. This result is consistent with a dynamic Jahn-Teller effect in the strong-coupling limit or with a static distortion stabilized by low-symmetry perturbations. The appearance of silent odd modes is in keeping with symmetry reduction of the hall, while activation of even modes is attributed to interband electron-phonon coupling and orientational disorder in the fulleride salt. Temperature dependences reveal a weak transition in the region 125-150 K in both C(60)(-) and counterion modes, indicating a bulk, rather than solely molecular, effect. Anomalous softening (with decreasing temperature) in several modes may correlate with the radial character of those vibrations. [S0163-1829(98)03245-7]

Product Design by Additive Manufacturing for Water Environments: Study of Degradation and Absorption Behavior of PLA and PETG

Additive manufacturing technologies are shifting from rapid prototyping technologies to end use or final parts production. Polymeric material extrusion processes have been broadly addressed with a specific definition of all parameters and variables for all different of technologies approaches and materials. Recycled polymeric materials have been studied due to the growing importance of the environmental awareness of the contemporary society. Beside this, little specific research has been found in product development applications for AM where the printed parts are in highly moisture environments or surrounded by water, but polymers have been for long used in such industries with conventional manufacturing approaches. This work focuses on the analysis and comparison of two different additively manufactured polymers printed by fused filament fabrication (FFF) processes using desktop-size printers to be applied for product design. The polymers used have been a recycled material: polyethylene terephthalate glycol (PETG) and polylactic acid (PLA). Degradation and water absorption behaviors of both materials are presented, analyzed and discussed in this paper, where different samples have been immersed in saturated solutions of water with maritime salt and sugar together with a control sample immersed in distilled water. The samples have been dimensionally and weight-controlled weekly as well as microscopically analyzed to understand degradation and absorption processes that appear in the fully saturated solutions. The results revealed how the absorption process is stabilized after a reduced number of weeks for both materials and how the degradation process is more remarked in the PLA material due to its organic nature