Effects of vacuum levels,carbon dioxide,and structural sizes of linked vessels on dump vessel vented

The method of explosion venting is widely used in industrial explosion-proof design due to its simple operation, economical and practical features. A dump vessel vented platform was built. By changing the vacuum level and the gas in the dump vessels and the structural size of linked vessels, the pressure in the explosion vessel and the dump vessel was compared, and the influencing factors of explosion venting investigated. The main conclusions are as follows: In the explosion venting process, the higher the vacuum in the dump vessel, the smaller the pressure peak of the explosion vessel and the dump vessel, and the faster the explosion pressure is lowered. When the dump vessel is under the same vacuum level and the gas in the dump vessel is CO₂, the maximum pressure of the explosion vessel and the dump vessel is less than the maximum pressure when the containment medium is air. Under the same vacuum condition, the larger the volume ratio of the dump vessel and the explosion vessel, the smaller the pressure peak of the explosion vessel, the faster the explosion pressure drops, and the volume of the dump vessel reaches or exceeds the explosion vessel. Increasing the volume ratio of the containment vessel to the explosion vessel facilitates protection of the explosion vessel and the containment vessel. Under the same vacuum condition, when the gas explosion in 113 L vessel vents into 22 L vessel, the longer the length of the pipe, the greater the maximum pressure in the spherical vessel. When the gas explosion in 22 L vessel vents into 113 L dump vessel, as the pipeline grows, the maximum pressure in the two vessels decreases, but the reduction is not significant. In practical application, it is recommended to use a vacuum of 0.08Mpa or more for the dump vessel vented, and the containment medium is CO_2.In terms of the structural size of the container, it is recommended that the ratio of the receiving container to the explosion container be as large as possible, and the pipe length be as long.     

Kinetic free mathematical model for the prediction of Kst values for organic dusts with arbitrary particle size distribution

Risk mitigation in production facilities has been an issue of great interest for decades, especially in activities which represent a serious hazard to human health, environment and industrial plants. Dust explosions are a major hazard in many industrial processes: only in the first part of 2019 (January–June) 34 dust explosions, mainly due to organic powders, occurred worldwide. An explosion may take place whenever there is the presence of combustible dusts, which are frequently generated by activities such as grinding, crushing, conveying and storage. Currently, a relatively expensive experimental test, carried out into a 20-L Siwek apparatus, is used to address the order of magnitude (class) of explosive dust: this piece of information is referred to as the deflagration index, K_st. At the current state, only a few pioneering models have been developed in order to predict the value of the K_st as a function of some relevant properties of the dust: e.g. particle size distribution (PSD), humidity, thermal conductivity, etc‥ Most of these models condense the information about the PSD of a given dust into an average value, referred to as D₅₀. In this work, a kinetic free mathematical model aimed at predicting the deflagration index for organic dusts is presented. This model, unlike the older ones, considers the whole particle size distribution for the computation of the deflagration index. In order to be implemented, only a single experimental K_st value (which works as a reference) and a particle size analysis on the dust are required. The model was validated using the whole granulometric distribution of three different organic powders (fosfomycin, sugar and niacin). In addition, the same estimations were done by considering only the D₅₀ data. It was noticed that, for highly polydispersed dusts, results were less accurate with respect to those obtained using the complete PSD, highlighting the importance of considering a complete granulometric distribution for process safety purposes.     

A methodology for calculating sample size to assess localized corrosion of process components

This paper proposes a methodology to estimate the required sample size to assess, with a specified precision, the localized corrosion of process components. The proposed methodology uses the extreme value and bootstrap methods. The results of estimated sample size ensure that the predicted maximum localized corrosion with the extreme value method is within an acceptable margin of error at a specified confidence level. Using the results of the proposed methodology, an equation is introduced to calculate sample size as a function of the acceptable margin of error, the population size, the standard deviation of corrosion data and the required confidence level. The probability of exceedance of critical limit of localized corrosion is also estimated. The methodology is explained through a case study of localized corrosion in process piping.     

Factorial analysis of diesel engine performance using different types of biofuels

In this study, several bio-source-fuels like fresh and waste vegetable oil and waste animal fat were tested at different injector pressures (120, 140, 190, 210 bar) in a direct-injection, naturally aspirated, single-cylinder diesel engine with a design injection pressure of 190 bar. Using 2k factorial analysis, the effect of injection pressure (Pi) and fuel type on three engine parameters, namely, combustion efficiency (etac), mass fuel consumption (mf), and engine speed (N) was examined. It was found that Pi and fuel type significantly affected both etac and mf while they had a slight effect on engine speed. Moreover, with diesel and biodiesels, the etac increased to a maximum at 190 bar but declined at the higher Pi value. In contrast, higher Pi had a favorable effect on etac over the whole Pi range with all the other more viscous fuels tested. In addition, the mass fuel consumption consistently decreased with an increase in Pi for all the fuels including the baseline diesel fuel, with which the engine consistently attained higher etac and higher rpm compared to all the other fuels tested.     

The Relative Efficiency of Ranked Set Sampling in Ordinary Least Squares Regression

Ranked set sampling was developed for situations where measurement cost is expensive compared with unit acquisition. This paper presents results of simulations and theory examining the impact of balanced ranked set sampling on the relative efficiencies of the slope and intercept estimators of an ordinary least squares regression. Perfect ranking of either the independent or the dependent variable is assumed throughout. In contradistinction to most of the published ranked set sampling work, it is demonstrated that balanced ranked set sampling offers at most little improvement in the relative efficiencies of the slope estimator at any sample size.     

城市植物叶面尘粒径和几种重金属(Cu、Zn、Cr、Cd、Pb、Ni)的分布特征

为研究城市植物叶面尘粒径及重金属元素(Cu、Zn、Cr、Cd、Pb、Ni)的分布规律和污染特征,以西安市不同功能区大叶女贞(Ligus-trum lucidum)和小叶女贞(Ligustrum quihoui)叶面尘为研究对象,用激光粒度分析仪测定叶面尘的粒径分布,用原子吸收分光光度计测定叶面尘重金属质量比,并探讨了叶面尘重金属的可能来源。结果表明,大叶女贞和小叶女贞叶面尘粒径小于50μm。前者叶面尘粒径累积曲线呈双峰分布,平均粒径和粒径峰值从大到小为相对清洁区、工业区、居住文教区、交通枢纽区、商业区;后者呈单峰分布,平均粒径和粒径峰值由大到小为工业区、居住文教区、交通枢纽区、商业区和相对清洁区。不同功能区叶面尘中Cu、Zn、Cr、Cd、Pb、Ni有明显的富集,其质量比分别为(325.5±72.6)mg/kg、(3 965.6±1 112.9)mg/kg、(349.2±149.3)mg/kg、(35.3±6.8)mg/kg、(1 182.0±355.1)mg/kg、(324.1±129.5)mg/kg,为陕西省土壤背景值的7.9～20.8、29.7～77.9、2.6～11.1、262.8～489.4、26.4～71.8和6.9～18.9倍。不同功能区2物种叶面尘各重金属质量比差异显著(p<0.001),物种间差异不显著(p>0.05)。叶面尘中Zn、Pb、Ni、Cr的质量比以工业区最高,Cu、Cd以交通枢纽区最高,其次为商业区,居住文教区和相对清洁区负荷最低。研究认为,叶面降尘中的重金属可能来自外源输入。     

Mediation of area and edge effects in forest fragments by adjacent land use

Habitat loss, fragmentation, and degradation have pervasive detrimental effects on tropical forest biodiversity, but the role of the surrounding land use (i.e., matrix) in determining the severity of these impacts remains poorly understood. We surveyed bird species across an interior-edge-matrix gradient to assess the effects of matrix type on biodiversity at 49 different sites with varying levels of landscape fragmentation in the Brazilian Atlantic Forest—a highly threatened biodiversity hotspot. Both area and edge effects were more pronounced in forest patches bordering pasture matrix, whereas patches bordering Eucalyptus plantation maintained compositionally similar bird communities between the edge and the interior and exhibited reduced effects of patch size. These results suggest the type of matrix in which forest fragments are situated can explain a substantial amount of the widely reported variability in biodiversity responses to forest loss and fragmentation.     

Estimating Sonoran pronghorn abundance and survival with fecal DNA and capture–recapture methods

Population abundance estimates are important for management but can be challenging to determine in low‐density, wide‐ranging, and endangered species, such as Sonoran pronghorn (Antilocapra americana sonoriensis). The Sonoran pronghorn population has been increasing; however, population estimates are currently derived from a biennial aerial count that does not provide survival or recruitment estimates. We identified individuals through noninvasively collected fecal DNA and used robust‐design capture–recapture to estimate abundance and survival for Sonoran pronghorn in the United States from 2013 to 2014. In 2014 we generated separate population estimates for pronghorn gathered near 13 different artificial water holes and for pronghorn not near water holes. The population using artificial water holes had 116 (95% CI 102–131) and 121 individuals (95% CI 112–132) in 2013 and 2014, respectively. For all locations, we estimated there were 144 individuals (95% CI 132–157). Adults had higher annual survival probabilities (0.83, 95% CI 0.69–0.92) than fawns (0.41, 95% CI 0.21–0.65). Our use of targeted noninvasive genetic sampling and capture–recapture with Sonoran pronghorn fecal DNA was an effective method for monitoring a large proportion of the population. Our results provided the first survival estimates for this population in over 2 decades and precise estimates of the population using artificial water holes. Our method could be used for targeted sampling of broadly distributed species in other systems, such as in African savanna ecosystems, where many species congregate at watering sites.     

Risk of Local Extinction of Odonata Freshwater Habitat Generalists and Specialists

Understanding the risk of a local extinction in a single population relative to the habitat requirements of a species is important in both theoretical and applied ecology. Local extinction risk depends on several factors, such as habitat requirements, range size of species, and habitat quality. We studied the local extinctions among 31 dragonfly and damselfly species from 1930 to 1975 and from 1995 to 2003 in Central Finland. We tested whether habitat specialists had a higher local extinction rate than generalist species. Approximately 30% of the local dragonfly and damselfly populations were extirpated during the 2 study periods. The size of the geographical range of the species was negatively related to extinction rate of the local populations. In contrast to our prediction, the specialist species had lower local extinction rates than the generalist species, probably because generalist species occurred in both low‐ and high‐quality habitat. Our results are consistent with source–sink theory. Riesgo de Extinción Local de Odonatos de Agua Dulce Generalistas y Especialistas de Hábitat     

Particle size and surface area effects on explosibility using a 20-L chamber

The Mine Safety and Health Administration (MSHA) specification for rock dust used in underground coal mines, as defined by 30 CFR 75.2, requires 70% of the material to pass through a 200 mesh sieve (<75 μm). However, in a collection of rock dusts, 47% were found to not meet the criteria. Upon further investigation, it was determined that some of the samples did meet the specification, but were inadequate to render pulverized Pittsburgh coal inert in the National Institute for Occupational Safety and Health (NIOSH) Office of Mine Safety and Health Research (OMSHR) 20-L chamber. This paper will examine the particle size distributions, specific surface areas (SSA), and the explosion suppression effectiveness of these rock dusts. It will also discuss related findings from other studies, including full-scale results from work performed at the Lake Lynn Experimental Mine. Further, a minimum SSA for effective rock dust will be suggested.