基于GT-Power柴油机颗粒捕集器捕集性能的仿真研究

利用GT-Power软件建立了柴油机颗粒捕集器(DPF)仿真模型,进行了仿真计算。研究了颗粒捕集器本身结构参数对其捕集效率与压降的影响。结果表明,影响颗粒捕集器捕集效率的主要参数有通道密度(CPSI)、过滤体孔隙率、过滤体微孔直径以及过滤壁厚度;影响颗粒物压降的主要参数有通道密度、过滤体渗透率、过滤体孔隙率以及过滤壁厚度。     

布袋过滤除尘中气固两相流的格子Boltzmann模拟

使用格子Boltzmann方法对含尘气体通过布袋滤料纤维的流动进行了数值模拟,采用拉格朗日方法跟踪了颗粒相中每个粒子的位置和速度并进行单向耦合计算。分析了气流通过纤维捕集体过程中的压降的变化规律,结果与达西渗透定律吻合。与此同时,对粒径小于1μm的气溶胶粒子在布袋纤维捕集体上的沉积规律展开了讨论。结果表明,粒径小于0.01μm的粒子的捕集主要受粒子的布朗随机扩散效应的控制;粒径大于0.1μm的粒子则主要依靠纤维滤料的拦截作用而沉积在捕集体表面;而粒径在0.01～0.1μm范围的粒子则具有较低的捕集效率。模拟结果为研究袋式除尘的过滤机理提供了依据。     

粉尘颗粒在单纤维表面沉积的计算机模拟

采用随机模拟方法模拟研究了粉尘颗粒在单纤维表面上的沉积过程,Kuwabara流场用于计算粉尘颗粒运动的轨迹,模拟中考虑了粉尘颗粒的粒径分布和单纤维在气流作用下的扭曲行为对粉尘颗粒沉积的影响.模拟结果表明.粉尘颗粒在单纤维表面上的沉积形态与分布特征依赖于Stokes数、粉尘颗粒粒径分布和纤维扭曲程度;模拟获得的粉尘树枝结构与相关文献提供的实验结果相似.     

柴油机微粒捕集器复合再生性能及其场协同分析

基于柴油机微粒捕集器瞬态复合再生机理,建立了CFD三维仿真模型,并利用漩涡破碎燃烧模型和场协同数学模型对柴油机微粒捕集器瞬态复合再生过程的速度矢量和温度梯度进行了数值模拟和场协同分析,结果表明,再生时间为175 s时的微粒捕集器过滤体后端壁面峰值温度达到1 184 K,且其过滤体内速度矢量和温度梯度的协同度最好,最优燃烧再生区域所占最大比值为0.58,表明此时微粒捕集器过滤体内再生燃烧速率最大,其再生效率最高。     

高炉除尘灰细微颗粒物单/双预荷电强化滤袋过滤特性

传统袋式除尘器对于细微颗粒物的捕集效率不甚理想,在袋式除尘器入口前增加预荷电装置是一种切实可行的强化其过滤特性的技术手段。设计搭建线板式直流高压预荷电器,研究了不同正/负匹配电压及风速对于双极预荷电高炉除尘灰电凝并行为的影响规律,对比分析了滤袋对未荷电、单极负荷电以及双极荷电高炉除尘灰细微颗粒物(PM_2.5)的捕集效率与压差特性,得到了不同预荷电方式高炉除尘灰细微颗粒物在滤袋表面沉积的微观形貌结构。结果表明：随着过滤风速(1.5～0.5 m·s^-1及匹配负电压(-16～-12 kV)的降低,双极荷电颗粒物凝并效率提高;高炉除尘灰细微颗粒物单/双预荷电均能提高滤袋的过滤效率;对于粒径<0.5μm颗粒,双极预荷电技术对滤袋捕集效率的强化效果好于单极预荷电技术;对粒径为0.5～2.5μm颗粒,单极预荷电技术的强化效果超过了双极预荷电技术;颗粒物单/双预荷电技术还使得滤袋阻力增量值及其增长速率值降低,且单极预荷电技术对于阻力降低效果更为明显。本研究可为利用单/双预荷电技术提升传统袋式除尘器对高炉除尘灰中细微颗粒物的捕集脱除特性提供参考。     

PPS滤布对柴油机排放PM的过滤效率

基于柴油机实验台架和颗粒捕集装置,采用聚苯硫醚(PPS)针刺毡滤布过滤柴油机排放的颗粒物(PM)。利用称重法,以Whatman玻璃纤维滤纸为对比滤纸,间接测试了3种PPS滤布的过滤效率;同时实验探索了表面涂覆聚四氟乙烯的PPS滤布的深床过滤时间。实验结果表明,3种滤布在180℃的加热条件下将出现颜色和形态的变化;3种滤布在深床过滤期对PM的平均过滤效率分别为78.8%、76.9%和83.7%;表面涂覆聚四氟乙烯的PPS滤布的深床过滤时间为15~20 min,此后其过滤效率可接近100%。     

孔道结构对柴油机微粒捕集器工作特性的影响

针对柴油机微粒捕集器中灰烬颗粒的沉积特征,设计了一种非对称孔道微粒捕集器,基于非对称孔道微粒捕集器对微粒捕集器再生模型进行修正,分析了非对称孔道对微粒捕集器再生特性的影响。研究结果表明,增大过滤体进出口截面比能减少微粒捕集器的压力损失,降低碳烟再生时过滤壁面的最大温度,且非对称孔道能减少灰烬沉积对再生时壁面最大温度的影响,因此根据过滤体壁面厚度适当增大进出口孔道截面比可以有效提升过滤体的碳烟承载量,延长微粒捕集器的车载使用寿命。     

新型电袋复合除尘器性能研究

为了提高布袋除尘器对细微粒子的捕集效率,同时降低压力损失,提出了一种新型的电袋复合除尘器,并利用这种新型的除尘器对2 500目的超细滑石粉进行了实验研究。通过普通布袋过滤、电袋复合过滤的对比实验研究,得到了电场强度、气布比、压损、清灰周期和除尘效率等参数的变化规律。实验结果表明,使用新型的复合除尘器过滤粉尘时,粉尘在进入袋室之前就被荷电,通过在滤料表面施加较强的静电场,使得被处理粉尘在滤料的表面有序堆积和排列,能有效地降低压力损失,提高过滤风速,除尘效率均达到97%以上。Vf=3.5 m/min,U=12.3 kV时,新型复合除尘器与普通布袋过滤相比压力损失降低了90 Pa;PM2.5的捕集效率提高了5.9%;清灰周期从10 min延长至36 min。     

旋风除尘器流场及浓度场实验与模拟

在研究旋风除尘器内气固两相的运动状况及分离机理方面,计算机模拟替代部分实验的方法能够优化设计旋风除尘器结构参数,提高其对微细颗粒的捕集效率,减少运行压力损失。本研究采用RSM模型和随机轨道模型对旋风除尘器内流场及浓度场进行模拟及实验。研究表明,旋风除尘器压力损失模拟结果与实验结果吻合较好,对于大于5μm的颗粒其捕集效率模拟结果与实验结果基本吻合;旋风除尘器外壁的颗粒浓度呈螺旋带状分布;如将排气管管径减少至原直径0.8倍,可使其对2μm颗粒捕集效率提高6.6%,但压力损失提高36.5%;颗粒的凝并作用有利于提高旋风除尘器微细颗粒的捕集效率。     

催化型微粒捕集器的再生与压降数值研究

采用新的再生机理对催化型微粒捕集器（CPF）深床捕集微粒的氧化再生过程进行了建模，并将微粒捕集器中的压降分成5个部分分别计算，对其压降特性进行了数值研究。结果表明，新模型对深床捕集微粒的氧化再生计算与实验值吻合良好，比原模型更能反映微粒沉积的实际过程，深床捕集微粒的压降计算值也更精确。在排气流量大、温度高的工况下，深床捕集微粒的压降先迅速增大再减小的现象明显。研究结果能为工程应用提供验证手段，为CPF的优化设计提供依据。     

Chloroaromatic pollutants in mussels incubated in two finnish watercourses polluted by industry

Concentrations of different chlorinated compounds were measured in mussels incubated in two polluted watercourses, a river (the River Kymijoki) and a lake (Lake Vanaja) for four weeks in summer 1995. The sum concentrations of polychlorinated phenols (PCP) and biphenyls (PCB) were both about 1 μg/g lipid weight (lw) in Lake Vanaja mussels, while in the River Kymijoki mussels PCPs were non-detectable and PCBs were measured 120 ng/g lIw. The concentrations of toxic polychlorinated dibenzo-p-dioxin (PCDD) and dibenzofuran (PCDF) congeners ranged between <17 and 370 pg/g Iw in Lake Vanaja mussels and between <38 and 11,000 pg/g lw in the River Kymijoki mussels. Polychlorinated diphenyl ethers (PCDE) were detected in the mussels incubated in the River Kymijoki (0.4–1.1 ng/g Iw), but not in those incubated in Lake Vanaja. Polychlorinated phenoxyanisoles (PCPA) were measured 33 ng/g lw and polychlorinated phenoxyphenols (PCPP) 300 ng/g lw in the mussels incubated in the River Kymijoki. PCPAs were also detected in reference samples, which were sediment and pike from the River Kymijoki and Baltic salmon, seal and white-tailed sea eagle.     

Radionuclides and trace elements in fish collected upstream and downstream of Los Alamos national laboratory and the doses to humans from the consumption of muscle and bone

Abstract

The purpose of this study was to determine radionuclide and trace element concentrations in bottom‐feeding fish (catfish, carp, and suckers) collected from the confluences of some of the major canyons that cross Los Alamos National Laboratory (LANL) lands with the Rio Grande (RG) and the potential radiological doses from the ingestion of these fish. Samples of muscle and bone (and viscera in some cases) were analyzed for ³H, ⁹⁰Sr, ¹³⁷Cs, ^totU, ²³⁸Pu, ^239,240Pu, and ²⁴¹Am and Ag, As, Ba, Be, Cr, Cd, Cu, Hg, Ni, Pb, Sb, Se, and Tl. Most radionuclides, with the exception of ⁹⁰Sr, in the muscle plus bone portions of fish collected from LANL canyons/RG were not significantly (p<0.05) higher from fish collected upstream (San Ildefonso/background) of LANL. Strontium‐90 in fish muscle plus bone tissue significantly (p<0.05) increases in concentration starting from Los Alamos Canyon, the most upstream confluence (fish contained 3.4E‐02 pCi g^‐1 [126E‐02 Bq kg^‐1]), to Frijoles Canyon, the most downstream confluence (fish contained 14E‐02 pCi g^‐1 [518E‐02 Bq kg^‐1]). The differences in ⁹⁰Sr concentrations in fish collected downstream and upstream (background) of LANL, however, were very small. Based on the average concentrations (±2SD) of radionuclides in fish tissue from the four LANL confluences, the committed effective dose equivalent from the ingestion of 46 lb (21 kg) (maximum ingestion rate per person per year) of fish muscle plus bone, after the subtraction of background, was 0.1 ± 0.1 mrem y^‐1 (1.0 ± 1.0 μSv y^‐1), and was far below the International Commission on Radiological Protection (all pathway) permissible dose limit of 100 mrem y^‐1 (1000 μSv y^‐1). Of the trace elements that were found above the limits of detection (Ba, Cu, and Hg) in fish muscle collected from the confluences of canyons that cross LANL and the RG, none were in significantly higher (p<0.05) concentrations than in muscle of fish collected from background locations.     

Book review

The Pesticide Manual ‐ A World Compendium, 8th Edition, C.R. Worthing, Editor and S.B. Walker, Assistant Editor, British Crop Protection Council, BCPC Publications Sales, Bear Farm, Binfield, Bracknell, Berkshire RG12 5QE, England. 1987, 1100 pp., UK £50; Overseas £56. ISBN 0–948404–01–9.     

Patterns of volatile metabolites and nonvolatile trichothecenes produced by isolates of <Emphasis Type="Italic">Stachybotrys,Fusarium, Trichoderma,Trichothecium</Emphasis> and <Emphasis Type="Italic">Memnoniella</Emphasis>

We reported previously that trichodiene, a volatile trichothecene derivative, was produced by a Stachybotrys isolate, also known to produce highly cytotoxic, non-volatile, macrocyclic trichothecenes (satrotoxins). We investigated the relationship between the production of trichodiene and various non-volatile trichothecenes for several molds. Volatile metabolites were concentrated by adsorption on Tenax TA and analyzed by GC/MS, while non-volatile metabolites were separated by HPLC, derivatized and analyzed by GC/MS. Stachybotrys chartarum isolates producing macrocyclic trichothecenes secreted significantly larger amounts of trichodiene and other sesquiterpenes than isolates which only produced simple trichothecenes. The amounts of secreted trichodiene were relatively small in all cases. With the exception of Memnoniella, which excreted small amounts of sesquiterpenes, the other isolates produced varying amounts of sesquiterpenes, including trichodiene, as well as simple tricothecenes, no detectable trichodiene, but large amounts of griseofulvin derivatives. In Stachybotrys there is apparently a correlation between trichodiene and macrocyclic trichothecene production. In the remaining isolates, there was no simple relationship between trichodiene and non-volatile trichothecene synthesis. Trichodiene is produced in larger amounts by Stachybotrys isolates, which also produce satratoxins, but it will be difficult to utilize this metabolite to detect toxic isolates in buildings due to the relatively small amounts excreted.     

Observations on the influence of water and soil pH on the persistence of insecticides

Abstract

The pH‐disappearance rate profiles were determined at ca. 25°C for 24 insecticides at 4 or 5 pH values over the range 4.5 to 8.0 in sterile phosphate buffers prepared in water‐ethanol (99: 1 v/v). Half‐lives measured at pH 8 were generally smaller than at lower pH values. Changes in half lives between pH 8.0 and 4.5 were largest (>1000x) for the aryl carbamates, carbofuran and carbaryl, the oxime carbamate, oxamyl, and the organophosphorus insecticide, trichlorfon. In contrast, half lives of phorate, terbufos, heptachlor, fensulfothion and aldicarb were affected only slightly by pH changes. Under the experimental conditions described half lives at pH8 varied from 1–2 days for trichlorfon and oxamyl to >1 year for fensulfothion and cyper‐methrin. Insecticide persistence on alumina (acid, neutral and basic), mineral soils amended with aluminum sulfate or calcium hydroxide to different pH values and four natural soils of different pH was examined. No correlation was observed between the measured pH of these solids and the rate of disappearance of selected insecticides applied to them. These observations demonstrate the difficulty of extrapolating the pH dependent disappearance behaviour observed in homogeneous solution to partially solid heterogeneous systems such as soil.     

The chemical stability of formulations of some hydrolyzable insecticides in aqueous mixtures with hydrolysis catalysts

Abstract

The active ingredients in commercial formulations of malathion, oxamyl, carbaryl, diazinon, and chlorpyrifos diluted to “spray tank”; concentrations with buffered distilled or natural water of pH 4–9 were stable for at least 24 hr. Formulations of trichlorfon were not stable at pH 7 or above but disappearance rates were slower than for the pure chemical in homogeneous solution. Cupric ion was observed to be an effective catalyst for the hydrolysis of a variety of pure organophosphorus insecticides but did not catalyze hydrolysis of the active ingredients of the formulations examined. Increasing the dilution of the formulation increased the susceptibility of malathion, oxamyl, and carbaryl to hydrolysis.     

Organochlorine compounds in a three-step terrestrial food chain

The concentrations of 15 organochlorine chemicals (PCBs and pesticides) were studied in a Central European oak wood food chain system: Great tit (Parus major), caterpillars (Tortrix viridana, Operophtera brumata, Erannis defoliaria), and oak-leaves (Quercus robur). Juvenile tits receive organochlorines from the mother via egg transfer and, eventually to a greater extent, from the caterpillar food source during nestling period. The concentrations of PCB 153 (2,2′,4,4′,5,5′-hexachlorobiphenyl, the most abundant in this study) was found in leaf material at ca. 1 ng/g, in caterpillars 10 ng/g, and in bird eggs 170 ng/g on an average and on a dry mass basis.     

Radionuclides in deer and elk from Los Alamos national laboratory and the doses to humans from the ingestion of muscle and bone

Abstract

This paper summarizes radionuclide concentrations (³H, ⁹⁰Sr, ¹³⁷Cs, ²³⁸Pu, ^239,240Pu, ²⁴¹Am, and ^totU) in muscle and bone tissue of mule deer (Odocoileus hemionus) and Rocky Mountain elk (Cervus elaphus) collected from Los Alamos National Laboratory (LANL), Los Alamos, New Mexico, lands from 1991 through 1998. Also, the committed effective dose equivalent (CEDE) and the risk of excess cancer fatalities (RECF) to people who ingest muscle and bone from deer and elk collected from LANL lands were estimated. Most radionuclide concentrations in muscle and bone from individual deer (n = 11) and elk (n = 22) collected from LANL lands were either at less than detectable quantities (where the analytical result was smaller than two counting uncertainties) and/or within upper (95%) level background (BG) concentrations. As a group, most radionuclides in muscle and bone of deer and elk from LANL lands were not significantly higher (p<0.10) than in similar tissues from deer (n = 3) and elk (n = 7) collected from BG locations. Also, elk that had been radio collared and tracked for two years and spent an average time of 50% on LANL lands were not significantly different in most radionuclides from road kill elk that have been collected as part of the environmental surveillance program. Overall, the upper (95%) level net CEDEs (the CEDE plus two sigma for each radioisotope minus background) at the most conservative ingestion rate (50 lbs of muscle and 13 lbs of bone) were as follows: deer muscle = 0.22 mrem y^‐1 (2.2 μSv y^‐1), deer bone = 3.8 mrem y^‐1 (38 μSv y^‐1), elk muscle = 0.12 mrem y^‐1 (1.2 μSv y^‐1), and elk bone = 1.7 mrem y^‐1 (17 μSv y^‐1). All CEDEs were far below the International Commission on Radiological Protection guideline of 100 mrem y^‐1 (1000 μSv y^‐1), and the highest muscle plus bone net CEDE corresponded to a RECF of 2E‐06, which is far below the Environmental Protection Agency upper level guideline of 1E‐04.     

Radionuclides in pinon pine (Pinus edulis) nuts from los alamos national laboratory lands and the dose from consumption

Abstract

One of the dominant tree species growing within and around the eastern portion of Los Alamos National Laboratory (LANL), Los Alamos, NM, lands is the pinon pine (Pinus edulis). Pinon pine is used for firewood, fence posts, and building materials and is a source of nuts for food—the seeds are consumed by a wide variety of animals and are also gathered by people in the area and eaten raw or roasted. This study investigated the (1) concentration of ³H, ¹³⁷Cs, ⁹⁰Sr, ^totU, ²³⁸Pu, ^{239, 240}Pu, and²⁴¹ Am in soils (0‐ to 12‐in. [31 cm] depth underneath the tree), pinon pine shoots (PPS), and pinon pine nuts (PPN) collected from LANL lands and regional background (BG) locations, (2) committed effective dose equivalent (CEDE) from the ingestion of nuts, and (3) soil to PPS to PPN concentration ratios (CRs). Most radionuclides, with the exception of ³H in soils, were not significantly higher (p < 0.10) in soils, PPS, and PPN collected from LANL as compared to BG locations, and concentrations of most radionuclides in PPN from LANL have decreased over time. The maximum net CEDE (the CEDE plus two sigma minus BG) at the most conservative ingestion rate (10 lb [4.5 kg]) was 0.0018 mrem (0.018 μSv); this is far below the International Commission on Radiological Protection (all pathway) permissible dose limit of 100 mrem (1000 μSv). Soil‐to‐nut CRs for most radionuclides were within the range of default values in the literature for common fruits and vegetables.     

Degradation and sorption of imidacloprid in dissimilar surface and subsurface soils

Degradation and sorption/desorption are important processes affecting the leaching of pesticides through soil. This research characterized the degradation and sorption of imidacloprid (1-[(6-chloro-3-pyridinyl)-methyl]-N-nitro-2-imidazolidinimine) in Drummer (silty clay loam) and Exeter (sandy loam) surface soils and their corresponding subsurface soils using sequential extraction methods over 400 days. By the end of the incubation, approximately 55% of imidacloprid applied at a rate of 1.0 mg kg^?1 degraded in the Exeter sandy loam surface and subsurface soils, compared to 40% of applied imidacloprid within 300 days in Drummer surface and subsurface soils. At the 0.1 mg kg^?1 application rate, dissipation was slower for all four soils. Water-extractable imidacloprid in Exeter surface soil decreased from 98% of applied at day 1 to > 70% of the imidacloprid remaining after 400 d, as compared to 55% in the Drummer surface soil at day 1 and 12% at day 400. These data suggest that imidacloprid was bioavailable to degrading soil microorganisms and sorption/desorption was not the limiting factor for biodegradation. In subsurface soils > 40% of ¹⁴C-benzoic acid was mineralized over 21 days, demonstrating an active microbial community. In contrast, cumulative ¹⁴CO₂ was less than 1.5% of applied ¹⁴C-imidacloprid in all soils over 400 d. Qualitative differences in the microbial communities appear to limit the degradation of imidacloprid in the subsurface soils.