Role of surface to volume ratio of zinc oxide arrester on energy absorption capability

Functional life of a zinc oxide arrester block is largely dependent on its energy absorption capability which is an important characteristic in ensuring enhanced reliability of a surge protection system. An arrester block is usually cylindrical in shape with two flat surfaces. Injected energy from the stroke of transient electrical surge into the arrester body is transformed into heat and dissipated through the surface of the disc body. This study has been conducted to observe whether the higher surface to volume (S/V) ratio of an arrester block enhances the capability of energy absorption or not. The round side or C-surface of the cylindrical disc was ground by diamond wheel to transform into hexagonal shape. By making this geometrical modification an increase of about 11% in S/V ratio was achieved for the hexagonal discs. Ten ZnO arrester blocks of both shapes were tested and the average energy absorption capability for the hexagonal discs was found to be 483 J.cm-3 compared to that of 357 J.cm-3 for the cylindrical discs. Thus, for the hexagonal discs a significant increase (35%) in energy absorption capability is observed which is attributable to increased S/V ratio of the arrester facilitating greater heat transfer. This knowledge can be useful in designing the geometry of the device for improved functional reliability of electrical system. Ke

Electrical performance of zinc oxide varistor using powders processed by different latex binders

The critical electrical parameters such as I-V characteristics, watt-loss and energy absorption capability etc. are the determinants for performance evaluation of ZnO varistors. In this regard there are a large number of contributing variables. Selection of proper binder in the processing of electro-ceramic powder is also a crucial factor. It imparts green strength, enhances compressibility and reduces density gradient within the green discs. Grain growth during sintering and subsequent microstructure of the varistor is also highly influenced by the binder system. It is envisaged that a disc with higher mechanical strength could be capable of withstanding more thermal stress due to temperature gradients. The energy absorption capability as well as high current performance can thus be enhanced. It was possible to generate varistor discs from the powder processed by the latex binder with better electrical performance than that of the powder processed with conventional binder of polyvinyl alcohol. Factorial analysis showed that the level of binder and solid concentration in the slurry had great influence on the energy absorption capability of ZnO varistor

Analysis of end crack in boiler tube

Boiler tube failures usually result in frequent forced outages, and ultimately in costly extended outages for major tubing replacement in a plant. There are several failure modes that may occur in a boiler tube, i.e. stress-corrosion cracking, pitting, water-side corrosion, fire-side corrosion, fatigue failure, overheating, dissimilar metal weld fatigue, mechanical fatigue and erosion. In this research the failure modes of boiler and its end cracks due to the dissimilar metal weld is analyzed. Hence data are collected and explored to determine the cause of failure and as a solution ceramic ferrule is suggested. The use of ceramic ferrule in boiler tube can eliminate the crack occurrence or delay the process due to thermal properties. The prevention of crack will reduce frequent maintenance and thus the cost of operation can be minimized

Wall thinning and creep damage analysis in boiler tube and optimization of operating conditions

The boiler tubes are operated continuously at high temperature and pressure. During operation,scales are formed in boiler tube due to tube geometries, flue gas and steam temperature. The remaining wall thickness decreases due to the formation of scale which eventually causes failure of the boiler tubes. In this investigation an iterative technique was used to determine the temperature distribution across the tube with the operating time. The operating time was considered up to 160,000 hours. The remaining life of the steam generator tube was found by finding hoop stress and Larson Miller Parameter from the Larson Miller Parameter curve for SA213-T22 material. By utilizing finite element modelling software, ANSYS 9/ANSYS 11 the temperature distribution across the steam generator tube was evaluated. The increase of heat transfer rate across the wall caused the oxide scale thickness to grow more rapidly than normal condition. It was also observed that due to formation of scale the thermal conductivity in the boiler tubes was affected and the remaining life of boiler tubes was decreased and accelerated creep damage. The ANSYS result was analyzed by Minitab 16 to determine the main and interactive effects of operating conditions. Steam temperature was influencing most the wall thinning and creep damage in comparison to the flue gas temperature. The interactive effects of both the parameters were also prominent. Moreover, the optimum operating condition was identified in order to maximizing the remnant life of the tubes while minimizing the creep rupture damage

Technical and economic feasibility of sensor technology for health/environmental condition monitoring

Continuous monitoring of health and environmental conditions is expected to be very helpful in identifying problem at an early stage and taking necessary measures and remedial actions. Analyzing an environment that has complex and highly variable emission sources at appropriate spatial and temporal scales is essential to understanding, monitoring, and controlling the system (1). The environmental condition in which a person lives largely determines the quality of his or her health. Detrimental effects due to increased levels of environmental (air and water) pollution can be mitigated, controlled, or avoided in many cases if early cautionary information is obtained. One cannot overemphasize the need for a reliable monitoring and controlling system for both the environment and health in order to create such a safe and secure situation (2). In this respect, the application of sensor and sensor technology has been playing a significant role. The recently acquired information and the technological capability to precisely engineer material property and behavior have offered opportunities to develop new sensor materials and innovative products, and to meet the demands for novel applications (3). Online sensing of material properties, combined with real-time control, has paved the way to achieving the lofty goals of self-directed and intelligent processing of information. In this regard, there has been a push to adopt the monitoring and controlling of human health and environmental conditions in many real-life problems. The benefits from the successful implementation and operation of such systems could be enormous. Naturally, environmental pollution is of great concern at present because of the imminence of the anticipated negative impact on the climate. This concern is worldwide as environmental pollution cannot be restricted within the boundaries of any country. Due to the rapid development and industrialization occurring globally, large amounts of pollutant gases and other toxic wastes are generated (4). The emission of such gases and the disposal of industrial waste are contributing greatly to increasing levels of pollution in the environment, and consequently the public is exposed to health risks and detrimental effects. Focusing on early detection and the prevention of environmental deterioration can help to mitigate the damages in various aspects of health, thus preventing catastrophic disaster. Recent developments in sensor technology make it possible to monitor personal exposure to air pollutants directly, despite the fact that the activity spaces through which a person is moving have changing concentration fields (5)

Securing superior properties of composite (PP+WF) through central composite design

Due to numerous attractive properties, use of composites is in increasing trend. Efforts are being made to develop new composites securing their useful properties at optimum level for more demanding applications. The purpose of this project is to optimize the mechanical properties of composite (polypropylene + wood fiber) using Central Composite Design (CCD) technique. Accordingly experiments were conducted to develop mathematical models in terms of three process parameters - composition (percentage of PP and wood fiber), injection pressure (bar), and time (second) for functional characteristics such as tensile strength and water absorption. Design expert software was used for convenience to carry out the analysis with a view to identifying the optimum level of the processing parameters for securing the desirable properties of the composite

Performance evaluation of zinc oxide varistor produced from powder under different spray drying conditions

I-V characteristics, wattloss behavior and energy absorption capability etc. are the critical characteristics for performance evaluation of ZnO varistors. In the long processing steps of this electro-ceramic with a considerable number of contributing variables, the preparation of pressing grade electro-ceramic materials is very important. It demands powders with high degree of compositional and microstructural homogeneity, high purity and reliability, proper shape and proper size and distribution. This kind of ceramic powder can be generated by spray drying. Apart from affecting the physical properties of varistor discs, the powder characteristics influence the grain growth and microstructure which are anticipated to affect the electrical behavior of the discs. To investigate this, varistor powder was produced from standard slurry under different spray drying conditions in pilot scale. Feed flow rate, atomizing air pressure and outlet drying air temperature were considered as input variables and nominal voltage, wattloss, clamp ratio, non-linear co-efficient and energy absorption capability were considered as response. It was found that nominal voltage, wattloss and energy absorption capability was highly influenced by spray drying variables but no significant influence was observed on clamp ratio and nonlinear co-efficient for both the pre-breakdown and breakdown region. Not only high but consistent energy absorption capability was achieved by optimizing spray drying conditions. Thus optimization of spray drying variables could help securing desirable varistor characteristics and enhanced reliability of the electrical system

Post-acute COVID-19 neuropsychiatric symptoms are not associated with ongoing nervous system injury

A proportion of patients infected with severe acute respiratory syndrome coronavirus 2 experience a range of neuropsychiatric symptoms months after infection, including cognitive deficits, depression and anxiety. The mechanisms underpinning such symptoms remain elusive. Recent research has demonstrated that nervous system injury can occur during COVID-19. Whether ongoing neural injury in the months after COVID-19 accounts for the ongoing or emergent neuropsychiatric symptoms is unclear. Within a large prospective cohort study of adult survivors who were hospitalized for severe acute respiratory syndrome coronavirus 2 infection, we analysed plasma markers of nervous system injury and astrocytic activation, measured 6 months post-infection: neurofilament light, glial fibrillary acidic protein and total tau protein. We assessed whether these markers were associated with the severity of the acute COVID-19 illness and with post-acute neuropsychiatric symptoms (as measured by the Patient Health Questionnaire for depression, the General Anxiety Disorder assessment for anxiety, the Montreal Cognitive Assessment for objective cognitive deficit and the cognitive items of the Patient Symptom Questionnaire for subjective cognitive deficit) at 6 months and 1 year post-hospital discharge from COVID-19. No robust associations were found between markers of nervous system injury and severity of acute COVID-19 (except for an association of small effect size between duration of admission and neurofilament light) nor with post-acute neuropsychiatric symptoms. These results suggest that ongoing neuropsychiatric symptoms are not due to ongoing neural injury

The global burden of cancer attributable to risk factors, 2010–19: a systematic analysis for the Global Burden of Disease Study 2019

BACKGROUND: Understanding the magnitude of cancer burden attributable to potentially modifiable risk factors is crucial for development of effective prevention and mitigation strategies. We analysed results from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019 to inform cancer control planning efforts globally. METHODS: The GBD 2019 comparative risk assessment framework was used to estimate cancer burden attributable to behavioural, environmental and occupational, and metabolic risk factors. A total of 82 risk–outcome pairs were included on the basis of the World Cancer Research Fund criteria. Estimated cancer deaths and disability-adjusted life-years (DALYs) in 2019 and change in these measures between 2010 and 2019 are presented. FINDINGS: Globally, in 2019, the risk factors included in this analysis accounted for 4·45 million (95% uncertainty interval 4·01–4·94) deaths and 105 million (95·0–116) DALYs for both sexes combined, representing 44·4% (41·3–48·4) of all cancer deaths and 42·0% (39·1–45·6) of all DALYs. There were 2·88 million (2·60–3·18) risk-attributable cancer deaths in males (50·6% [47·8–54·1] of all male cancer deaths) and 1·58 million (1·36–1·84) risk-attributable cancer deaths in females (36·3% [32·5–41·3] of all female cancer deaths). The leading risk factors at the most detailed level globally for risk-attributable cancer deaths and DALYs in 2019 for both sexes combined were smoking, followed by alcohol use and high BMI. Risk-attributable cancer burden varied by world region and Socio-demographic Index (SDI), with smoking, unsafe sex, and alcohol use being the three leading risk factors for risk-attributable cancer DALYs in low SDI locations in 2019, whereas DALYs in high SDI locations mirrored the top three global risk factor rankings. From 2010 to 2019, global risk-attributable cancer deaths increased by 20·4% (12·6–28·4) and DALYs by 16·8% (8·8–25·0), with the greatest percentage increase in metabolic risks (34·7% [27·9–42·8] and 33·3% [25·8–42·0]). INTERPRETATION: The leading risk factors contributing to global cancer burden in 2019 were behavioural, whereas metabolic risk factors saw the largest increases between 2010 and 2019. Reducing exposure to these modifiable risk factors would decrease cancer mortality and DALY rates worldwide, and policies should be tailored appropriately to local cancer risk factor burden

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries