On the response of a lean-premixed hydrogen combustor to acoustic and dissipative-dispersive entropy waves

Combustion of hydrogen or hydrogen containing blends in gas turbines and industrial combustors can activate thermoacoustic combustion instabilities. Convective instabilities are an important and yet less investigated class of combustion instability that are caused by the so called “entropy waves”. As a major shortcoming, the partial decay of these convective-diffusive waves in the post-flame region of combustors is still largely unexplored. This paper, therefore, presents an investigation of the annihilating effects, due to hydrodynamics, heat transfer and flow stretch upon the nozzle response. The classical compact analysis is first extended to include the decay of entropy waves and heat transfer from the nozzle. Amplitudes and phase shifts of the responding acoustical waves are then calculated for subcritical and supercritical nozzles subject to acoustic and entropic forcing. A relation for the stretch of entropy wave in the nozzle is subsequently developed. It is shown that heat transfer and hydrodynamic decay can impart considerable effects on the entropic response of the nozzle. It is further shown that the flow stretching effects are strongly frequency dependent. The results indicate that dissipation and dispersion of entropy waves can significantly influence their conversion to sound and therefore should be included in the entropy wave models

Fingering and strain localization in porous media during imbibition processes

Fingered infiltration of a wetting fluid through a porous network is a widely studied subject in the field of fluid mechanics. However, the effect of this heterogeneous percolation on the response of granular materials, in particular fine-grained soils, is a poorly investigated and badly understood topic which deserves deep analysis, considering, among others, possible applications in soil remediation and underground energy storage. This paper presents a first application of a new formulation of unsaturated poromechanics based on a phase field approach that allows to characterize on the one hand the occurrence of fingering hydraulic instabilities and on the other one to capture their effects on the irreversible, and possible unstable, deformation of the solid skeleton. The envisaged application concerns the behavior of fine-grained soils whose dilatant/contractant behavior is more and more attracting the interest of the scientific community both in the fields of experimental research and numerical modeling

COVID-19-related strokes in adults below 55Â years of age: a case series

Background: Coronavirus infection is a novel respiratory disease affecting people across the world. Although the majority of patients present with fever, dyspnea, cough, or myalgia, various signs and symptoms have been reported for this disease. Recently, neurological symptoms have been noticed in patients with COVID-19 with unknown etiology. However, the occurrence of strokes in young and middle aged patients with COVID-19 is not fully explained. Methods: In this series, six patients younger than 55 years of age with diagnosis of stroke and a confirmed diagnosis of COVID-19 were evaluated for symptoms, lab data, imaging findings, and outcomes from March 2020 to the end of April 2020 from all stroke cases in a tertiary academic hospital. Patients older than 55 and all others who had evidence of cardiac abnormalities (arrhythmia/valvular) were excluded. Results: Fever, myalgia, cough, and dyspnea were the most common clinical symptoms noted in 66.66 (4/6), 66.66 (4/6), 50 (3/6), and 50 (3/6) of the patients, respectively. The mean ± standard deviation (SD) of National Institutes of Health Stroke Scale (NIHSS) for the patient was 10.16 ± 7.13 (ranged 5�24). The most involved area was middle cerebral artery (MCA) (five in MCA versus one in basal ganglia) and the majority of our patients had a low lung involvement score (mean ± SD: 13.16 ± 6.49 out of 24). Finally, one patient was deceased and rest discharged. Conclusion: Stroke may be unrelated to age and the extent of lung involvement. However, different factors may play roles in co-occurrence of stroke and COVID-19 and its outcome. Future studies with long-term follow-up and more cases are needed to assess prognostic factors. © 2020, Fondazione Società Italiana di Neurologia

Most effective combustion technologies for reducing Nox emissions in aero gas turbines

The growth in air transportation volume has important global environmental impacts associated with the potential for climate change. Jet aircraft emissions are deposited directly into the upper atmosphere and some of them have a greater warming effect than gases emitted closer to the surface. One of the key issues that is addressed in virtually every aero gas turbine application is emissions, particularly Nox emissions. There are different technologies for nitrogen oxide emission control in aircraft gas turbines. In this paper, we have briefly reviewed the technologies with the greatest potential to reduce Nox emissions in aero engines

Development of an Augmented Conceptual Design Tool for Aircraft Gas Turbine Combustors

Combustor design is the most unreliable and challenging portion in the design process of a gas turbine. To ensure the proper performance, many experimental tests must be performed on a combustor in the industry. The above mentioned design phase is costly and time consuming. This paper focused on an automated and augmented conceptual design methodology for conventional combustors. The design tool developed for this study employs empirical and semi-empirical models which include two main parts of the combustor, the reference diameter and area as well as the component design. The necessity of this work arose from an urgent need for comprehensive and fast generation data in the conceptual design phase of a combustion chamber. This automated and comprehensive tool, equipped with the capacity to provide many details, has a considerable impact on the reduction of further experimental effort. Also, the said tool is equipped with a geometrical model generation section that has application in the future design phases, e.g., detail design

Experimental Study of Injection Characteristics of a Multi-hole port injector on various Fuel Injection pressures and Temperatures

The structures of the port injector spray dominates the mixture preparation process and strongly affect the subsequent engine combustion characteristics over a wide range of operating conditions in port-injection gasoline engines. All these spray characteristics are determined by particular injector design and operating conditions. In this paper, an experimental study is made to characterize the breakup mechanism and spray characteristics of a injector with multi-disc nozzle (SAGEM,D2159MA). A comparison was made on injection characteristics of the multi-hole injectors and its effects on various fuel pressure and temperature. The distributions of the droplet size and velocity and volume flux were characterized using phase Doppler anemometry (PDA) technique. Through this work, it was found that the injector produces a finer spray with a wide spray angle in higher fuel pressure and temperature

Experimental Study of Injection Characteristics of a Multi-hole port injector on various Fuel Injection pressures and Temperatures

The structures of the port injector spray dominates the mixture preparation process and strongly affect the subsequent engine combustion characteristics over a wide range of operating conditions in port-injection gasoline engines. All these spray characteristics are determined by particular injector design and operating conditions. In this paper, an experimental study is made to characterize the breakup mechanism and spray characteristics of a injector with multi-disc nozzle (SAGEM,D2159MA). A comparison was made on injection characteristics of the multi-hole injectors and its effects on various fuel pressure and temperature. The distributions of the droplet size and velocity and volume flux were characterized using phase Doppler anemometry (PDA) technique. Through this work, it was found that the injector produces a finer spray with a wide spray angle in higher fuel pressure and temperature

The Air Pollution at Rochester: Long-Term Trends

There have been a number of changes in the sources of air pollutant in the northeastern United States since 2001. Trend analyses of monthly averages were performed on PM 2.5, ionic species, elemental carbon (EC), organic carbon (OC) and gaseous pollutants collected between 2001 and 2015 for NYS Department of Environmental Conservation sites in Rochester. Non-parametric (Mann-Kendall regression with Sen’s slope) and parametric (weighted linear and non-linear regressions) approaches were applied to estimate the trends and seasonality. We fitted the different models to monthly averages of each species for each month over the 15 years of available data. Separating the data by month removes their seasonal dependence. The unequal number of attainable samples averaged to provide monthly asset value was accounted for by weighting each month proportional to its number of available daily concentration values. Sulfate and nitrate showed downward trends. For almost all of the species over the whole, the weighted linear parametric modeling yielded steeper slopes than the non-parametric Mann-Kendall approach. For sulfate, the slopes = -0.20 and -0.15 μg m -3 year -1, respectively. These trends will be compared to changes in emissions in the upwind source domain

The Air Pollution at Rochester: Long-Term Trends

There have been a number of changes in the sources of air pollutant in the northeastern United States since 2001. Trend analyses of monthly averages were performed on PM 2.5, ionic species, elemental carbon (EC), organic carbon (OC) and gaseous pollutants collected between 2001 and 2015 for NYS Department of Environmental Conservation sites in Rochester. Non-parametric (Mann-Kendall regression with Sen’s slope) and parametric (weighted linear and non-linear regressions) approaches were applied to estimate the trends and seasonality. We fitted the different models to monthly averages of each species for each month over the 15 years of available data. Separating the data by month removes their seasonal dependence. The unequal number of attainable samples averaged to provide monthly asset value was accounted for by weighting each month proportional to its number of available daily concentration values. Sulfate and nitrate showed downward trends. For almost all of the species over the whole, the weighted linear parametric modeling yielded steeper slopes than the non-parametric Mann-Kendall approach. For sulfate, the slopes = -0.20 and -0.15 μg m -3 year -1, respectively. These trends will be compared to changes in emissions in the upwind source domain

A systematic review of anti-Entamoeba histolytica activity of medicinal plants published in the last 20 years

Amoebiasis has emerged as a major health problem worldwide. It is endemic in the present scenario is different and sub-tropical regions especially in Asia, Latin America and also in Africa. Causative of amoebiasis is a protozoan known as Entamoeba histolytica. We screened all the databases such as PubMed, Science Direct, Medline and Google Scholar by using the keywords 'anti-Entamoeba histolytica activity of medicinal plants, anti-Entamoeba histolytica activity of herbal drugs, the anti-amoebic activity of natural drugs'. In the present study, we found 7861 articles, where all articles were screened for bias analysis and included 32 full-matching articles in total reporting the use of medicinal plants as a remedy for amoebiasis. Through these articles, we found 42 herbs having anti-amoebic activity. In bias analysis, we also found four articles under high bias risk. In our study, seven medicinal plants were concluded to possess the most potent anti-amoebic activity based on their IC50 value, which was less than 1 μg mL-1. On bias analysis, we found four articles with high bias risk, hence these studies can be repeated for better results. Copyright © The Author(s) 2021. Published by Cambridge University Press