The use of an atmospheric dispersion model to determine influence regions in the Prince George,B.C. airshed from the burning of open wood waste piles

A means of determining air emission source regions adversely influencing the city of Prince George, British Columbia, Canada from potential burning of isolated piles of mountain pine beetle-killed lodge pole pine is presented. The analysis uses the CALPUFF atmospheric dispersion model to identify safe burning regions based on atmospheric stability and wind direction. Model results show that the location and extent of influence regions is sensitive to wind speed, wind direction, atmospheric stability and a threshold used to quantify excessive concentrations. A concentration threshold based on the Canada Wide PM_2.5 Standard is used to delineate the influence regions while Environment Canada's (EC) daily ventilation index (VI) is used to quantify local atmospheric stability. Results from the analysis, to be used by air quality meteorologists in assessing daily requests for burning permits, are presented as a series of maps delineating acceptable burning locations for sources placed at various distances from the city center and under different ventilation conditions. The results show that no burning should be allowed within 10 km of the city center; under poor ventilation conditions, no burning should be allowed within 20 km of the city center; under good ventilation conditions, burning can be allowed within 10–15 km of the city center; under good to fair ventilation conditions, burning can be allowed beyond 15 km of the city center; and if the wind direction can be reliably forecast, burning can be allowed between 5 and 10 km downwind of the city center under good ventilation conditions.     

Assessment of air dispersion characteristic in underground mine ventilation: Field measurement and numerical evaluation

The environmental safety of an underground mine depends strongly on its ventilation system. An efficient ventilation system provides fresh air, removes hazardous gases and dust, and maintains the temperature and humidity at appropriate levels. One of the most important factors in removing hazardous gases and dust is the dispersion behaviour in the mine network. This factor determines the longitudinal spreading and the average air residence time of gases or particulate matter throughout the mine. This paper describes tracer gas measurement in an underground mine and the utilisation and analysis of the dispersion characteristics using numerical simulations. The concentration–time curve obtained from the measurement is simulated to evaluate the effective diffusion coefficient that reflects the general dispersion characteristic of an entire mine. The evaluated values of effective diffusion coefficient are then compared to other data from several studies. The diffusivities obtained in this study were higher than other analytical and empirical results. More research is still required to identify the main factors causing such higher diffusivities. However, the results from the present work can be an important standpoint for future work. Numerical simulation conducted in this research was confirmed to be effective in detecting several leakage paths occurring in the mine ventilation network.     

Effect of pressure for dust dispersion on minimum ignition temperature

The existing technical standards for determining the minimum ignition temperature (MIT) of dust clouds are inadequate. According to existing technical standards, this study expands the test pressure conditions. The MIT of dust clouds can be determined by a variety of different dispersion pressures, that is, 0.02, 0.04, 0.06, 0.08 and 0.1 MPa. But, whether the MIT of dust clouds tested under different dispersion pressures is consistent is lacking in the corresponding exploration. In this study, a set of measurement system of instantaneous concentration and particle size was established, which can observe the flow of dust clouds and the distribution of the instantaneous particle size and concentration of dust clouds in the heating furnace tube. On this basis, the MIT of dust clouds is determined, and the physical mechanism of dispersion pressure affecting the MIT of dust clouds is revealed. The results show that the MIT of dust clouds is consistent when the dispersion pressure in the range of 0.02–0.06 MPa. When the dispersion pressure is not in this range, the MIT of the dust clouds is very different due to the obvious increase of the instantaneous particle size of the dust clouds.     

Simulation and source identification of X-ray contrast media in the water cycle of Berlin

This article describes the development of a model to simulate the fate of iodinated X-ray contrast media (XRC) in the water cycle of the German capital, Berlin. It also handles data uncertainties concerning the different amounts and sources of input for XRC via source densities in single districts for the XRC usage by inhabitants, hospitals, and radiologists. As well, different degradation rates for the behavior of the adsorbable organic iodine (AOI) were investigated in single water compartments. The introduced model consists of mass balances and includes, in addition to naturally branched bodies of water, the water distribution network between waterways and wastewater treatment plants, which are coupled to natural surface waters at numerous points. Scenarios were calculated according to the data uncertainties that were statistically evaluated to identify the scenario with the highest agreement among the provided measurement data. The simulation of X-ray contrast media in the water cycle of Berlin showed that medical institutions have to be considered as point sources for congested urban areas due to their high levels of X-ray contrast media emission. The calculations identified hospitals, represented by their capacity (number of hospital beds), as the most relevant point sources, while the inhabitants served as important diffusive sources. Deployed for almost inert substances like contrast media, the model can be used for qualitative statements and, therefore, as a decision-support tool.     

Modelling of time-varying dispersion for elevated pressurised releases without rainout

Many commonly used atmospheric dispersion models are limited to continuous or instantaneous releases only, and cannot accurately simulate time-varying releases. The current paper discusses a new enhanced dispersion formulation accounting for time-varying effects resulting from a pressure drop in a vessel or pipe, and presuming no rainout. This new formulation is implemented in the Unified Dispersion Model (UDM), and is planned to be included in a future version of Phast.First existing methods are summarised for modelling finite-duration and time-varying releases, and limitations of these methods are identified.Secondly the new mathematical model is summarised. The new formulation presumes a number of ‘observers’ to be released at successive times from the point of discharge. The UDM carries out pseudo steady-state calculations for each observer, where the release data correspond to the time at which the observer is released. Subsequently the model applies a correction to the observer concentrations to ensure mass conservation when observers move with different velocities. Finally effects of along-wind diffusion (due to ambient turbulence) are included by means of Gaussian integration over the downwind distance. This results in reduced concentrations while the cloud travels in the downwind direction.The benefits of the new UDM methodology are illustrated for the case of a H₂S toxic release from a long pipeline representative of some extremely sour fields in the Middle East that are now being developed. Using corrected observer concentrations and along-wind diffusion significantly reduces toxic effect distances when compared to the current Phast 7.1 approach.     

Gas leakage consequence modeling for buried gas pipelines

One of conservation transfer methods for such widely-used gases as natural gas and hydrogen is buried pipelines. Safety of these pipelines is of great importance due to potential risks posed by inefficiencies of the pipelines. Therefore, an accurate understanding of release and movement characteristics of the leaked gas, i.e. distribution and speed within soil, the release to the ground surface, the movement of hydrogen gas through the ground, gas underground diffusion, gas dispersion in atmosphere, and following consequences, are very important in order to determine underground dispersion risks. In the present study, consequences of gas leakage within soil were evaluated in two sub-models, i.e. near-field and far-field, and a comprehensive model was proposed in order to ensure safety of buried gas supply pipelines. Near-field model which is related to soil and ground and its output is the gas released at different points and times from ground surface and it was adopted as input of far-field sub-model which is dispersion model in atmosphere or an open space under the surface. Validation of near-field sub-model was performed by the experimental data obtained by Okamoto et al. (2014) on full-scale hydrogen leakage and then, possible scenarios for far-field sub-model were determined.     

重气连续泄漏扩散的风洞模拟实验与数值模拟结果对比分析

将重气连续泄漏的风洞模拟实验结果与SLAB重气扩散模型的预测结果进行了对比 ,分析了实验结果与模型预测结果的一致性 ,剖析了重气连续扩散的特点 ,特别是风速对重气连续泄漏扩散的影响 ,提出了在风洞模拟实验及扩散模型方面下一步应做的工作     

Investigations into the influence of dustiness on dust explosions

A new safety characteristic the “dustiness” according to VDI 2263 – part 9 (Verein Deutscher Ingenieure, 2008) is investigated. Dustiness means the tendency of a dust to form clouds. The paper deals with the influence of the dustiness on vented dust explosions. In order to look into the effects of the dustiness on dust cloud formation and explosion properties experiments and simulations in a vertical dust dispersion glass tube apparatus were carried out.Preliminary explosion experiments showed that the dustiness has an influence on the reduced explosion pressure in a vented 75 L test apparatus. Dusts with comparable p_max and K_St values and different dustiness were tested. Dusts with higher dustiness produced higher overpressures, despite comparable safety characteristics. In order to verify the results for applications in the process industries further tests with different settings are planned as well as industrial scale experiments. Characteristics of the dust such as particle size, density, specific surface area and particle shape, which influence the dispersibility, have been determined experimentally.The Euler/Lagrange and the Euler/Euler approaches are compared for simulating an exemplary dust/air mixture. Especially sedimentation and the ability of the approaches to simulate the tendency of dust to stay airborne were investigated. The Euler/Lagrange approach is better suited for simulating local dust concentrations, particle size distributions and particle forces. It could be used to point out regions of high dust concentrations in a vessel. With the Euler/Euler method it is possible to achieve fast solutions for one specified diameter, but the simulated dust/air mixtures are always more homogenous than in reality. ANSYS CFX version 13 was used in all simulations.     

Microhabitat selection in the simple oribatid community dwelling in epilithic moss cover (Acari: Oribatida)

The moss cover of a roof was studied as the model of a simple habitat divided into microhabitats by the members of a community of saprophagous mites. This community consisted of two species of oribatid mites: Scutovertex minutus and Trichoribates trimaculatus. They were extracted from moss onto moist paper, and subsequently, their mobility, responses to moisture fluctuation, and food selection were tested in laboratory experiments. For the nutritional biology, the microanatomy of their alimentary tract was examined according to the system of histological characteristics formulated in the laboratory of the author (type of food, digestive activity of gut walls, etc.). The paraplast sections of the mites were stained by Masson triple stain for these purposes. Moreover, the enzymological tests (chitinase and cellulase activities) were performed to detail the digestive processes. Such an approach was applied to field-sampled specimens as well as to those in the laboratory experiments. These above-mentioned data were discussed with respect to microhabitat selection, vertical and horizontal distribution, and dispersal ability of these two oribatid mites sharing this habitat. These two species differ in several characteristics from each other and these differences resulted in their different microhabitat choices and role in the habitat as a whole.