• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 441
  • 84
  • 60
  • 55
  • 47
  • 25
  • 15
  • 11
  • 11
  • 11
  • 11
  • 11
  • 11
  • 9
  • 8
  • Tagged with
  • 985
  • 85
  • 72
  • 64
  • 63
  • 50
  • 46
  • 45
  • 44
  • 42
  • 41
  • 40
  • 39
  • 38
  • 37
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
91

Experimental Investigation of Microparticle Sand Sticking Probability from 1000°C to 1100°C

Boulanger, Andrew James 05 December 2017 (has links)
Increasing commercial and military aircraft operations in arid environments are increasing the likelihood of sand and dust ingestion. Turbine engines are particularly susceptible to the ingestion of sand and dust, which can erode cold-section components and deposit onto hot-section components. Ultimately, the erosion and deposits will shorten the operational lifespan of these engines and limit their availability thereby increasing maintenance costs and risking safety. Mitigating these risks has become more prevalent in recent years due to increasing combustion temperatures in effort to increase fuel efficiency. Increasing combustion temperatures directly increases deposit formation onto hot-section components. Monitoring deposit formation on existing turbine engine platforms and improving deposit resilience on new designs has been the industry focus for the last two decades. This study focused on statistically modeling the initial onset of microparticle deposits onto an analogous hot-section surface. Generally, as deposits accumulate onto a hot-section surface, the existing deposit formation is more likely to bond with incoming particulate at a faster rate than an exposed bare surface. Predicting the initial deposits onto a bare surface can determine the accelerated deposition rate depending on subsequent particulate impinging onto the surface. To emulate the initial deposits, a HASTELLOY® X test coupon was exposed to 20 μm to 40 μm samples of Arizona Road Test Dust (ARD) at varying loadings and aerosol densities. The Virginia Tech Aerothermal Rig was used for all test scenarios at flow-particle temperatures between 1000°C to 1100°C. Several statistical models were developed as a function of many independent variables, culminating with a final sticking probability (SP) model. Overall, the SP of individual ARD particulate is a primary function of flow-particle temperature and normal impact momentum. Tangential impact momentum of a particle will decrease the SP, while surface temperatures reaching isothermal conditions with the flow will increase SP. However, there are specific cases where lower surface temperatures and high particle temperatures result in a high SP. Particle size was a strong predictor of SP where particles between 10 μm to 19 μm were 5 to 10 times greater than the 19 μm to 40 μm range. Additional studies will be necessary to examine some additional parameters that become more prominent with smaller particle sizes. Ultimately, the intention of the models is to assist turbine engine designers to improve resilience to deposit formation on hot-section components. / PHD / Dust ingestion by propulsion turbine engines can have severe negative implications on the operational safety of an aircraft. Recently, increased air traffic, both military and commercial, in desert regions has caused many aircraft engine designers to improve the resilience to dust ingestion effects. One of the detrimental mechanisms is hot particle deposits in the combustion and exhaust sections. This dissertation evaluates deposit formation using carefully developed high temperature experiments. In general, deposit formation can negatively change flow characteristics inside the engine that can limit available power and safety margins. Likewise, deposits can reduce or stop cooling needed for hot-section parts inside a jet engine. Hot-section components need cooling since the main gas path operation temperatures of a jet engine typically exceed the melting points of common high temperature metals. During dust ingestion events, deposits will initially adhere to a hot metallic or ceramic surface inside the engine. Subsequent deposit accumulation will occur at a faster rate since incoming particles will more readily adhere to existing deposits than to a metallic or ceramic surface. The experimental work in this dissertation focused only on quantifying the initial individual particle deposits on a HASTELLOY®-X surface between 1000°C to 1100°C. Arizona Road Dust was the particulate selected for all testing. The dust has sizes ranging between 10 µm to 40 µm. The sticking probability or the likelihood a particle would deposit per an impact was less than 5% for all tests performed. Particles smaller than 19 µm had a sticking probability up to 5% while larger particles were generally less than 3%. Effectively, this implies that the initial deposits onto a hot engine surface are strongly dependent on the smallest particles. Propulsion turbine engine designers can utilize this information to develop mitigation methods against deposit formation of the smallest particles that are ingested. Ultimately, the research presented in this work is intended to improve operational safety of current and future aircraft.
92

Dammbekämpning : Södra Cell Mönsterås / Dust Control : Södra Cell Mönsterås

Fransén, Erik, Oskarsson, Arvid January 2024 (has links)
Södra Cell Mönsterås (SCMS) är en betydande producent av pappersmassa som årligen producerar runt 750 000 ton. Vid produktion av pappersmassa så blir bark en biprodukt. Barken barkas av i renseriet och transporteras upp till barkpannan och rökgastorken via transportörsband. SCMS står inför betydande problem med dammbildning när barken byter transportband, särskilt med en höjdskillnad på 5–6 meter. Ett övertryck bildas i kanalen under övergången och alla små partiklar trycks ut och det resulterar i en dammfylld miljö.Syftet med examensarbetet är således att förklara hur dammbildning uppstår och vad det finns för risker med det. Men huvudmålet är att hitta den bästa lösningen för att minska dammbildningen runt transportörerna. Denna undersökning kommer att vara relevant för mer än bara SCMS då detta är ett problem som är vanligt förekommande i olika industrier. Med hjälp av vår forskning så kommer SCMS få en bra överblick över vad det finns för relevanta lösningar och vad det skulle kosta. Uppgiftsbeställningen kan ses i bilaga 1.Både i miljö och arbetssyfte är detta ett problem som måste lösas. Att andas in barkdamm är hälsofarligt och kan även vara cancerframkallande vid vissa trädslag. Mestadels av trädamm som vi andas in kan vår näsa stoppa, men är det nog små dammpartiklar kan de leta sig ner i lungorna.Under forskningen kontaktades relevanta industrier som har eller haft liknande problem. Studenterna kontaktade även kunnigt folk inom detta område och diskuterade olika lösningar på problemet. Resultatet av dessa kontakter var att det finns många som stött på liknande problem men inte exakt likadana, vilket gör att det inte fanns en universell lösning innan undersökningen var slutförd.Undersökningen visade att det finns många olika lösningar för att hantera dammbildningen vid omlastningsstationen på SCMS under barktransportens bandbyte. Många av dessa lösningar hade dock betydande nackdelar, såsom höga tekniska krav, höga kostnader eller för stor potentiell påverkan på processen.Slutligen kom studenterna fram till att den bästa lösningen var att leda bort dammet med en ventilationskanal till en behållare, där vattendysor sprayar ner dammet i avloppet. Denna metod påverkar barken minimalt medan den effektivt avlägsnar dammet. Dessutom var kostnaden för denna lösning rimlig, vilket gör den både säker och ekonomiskt fördelaktig. Slutkommentar från SCMS visas i bilaga 2, denna visar att studenterna har löst uppgiften på ett bra sätt. / Södra Cell Mönsterås (SCMS) is a significant producer of pulp, annually producing around 750,000 tons. In the production of pulp, bark becomes a residual product. The bark is stripped off in the cleaning plant and transported up to the bark boiler and the bark furnace via conveyor belts. SCMS faces significant problems with dust formation when the bark changes conveyor belts, especially with a height difference of 5-6 meters. An overpressure is formed in the channel during the transition, and all small particles are pushed out, resulting in a dusty environment.The purpose of the thesis is thus to explain how dust formation occurs and what risks are associated with it. However, the main goal is to find the best solution to reduce dust formation around the conveyor. This study will be relevant to more than just SCMS as this is a fairly common problem. With the help of our research, SCMS will get a good overview of relevant solutions and their costs.Both environmentally and from a work perspective, this is a problem that must be solved. Inhaling wood dust is hazardous to health and can even be carcinogenic for certain tree species. Most of the wood dust we inhale can be stopped by our nose, but if the dust particles are small enough, they can penetrate into the lungs.During the research, relevant industries that have or have had similar problems were contacted. The students also contacted knowledgeable people in this field and discussed various solutions to the problem. The result of these contacts was that many had encountered similar problems but not exactly the same, which meant that there was no universal solution until the investigation was completed.The investigation resulted in finding many different solutions for managing dust formation at SCMS during bark transport belt changes. However, many of them were found to have significant drawbacks, such as technical requirements, high costs, or too much potential impact on the process.Finally, the students concluded to use the solution where the dust is directed away through a ventilation duct to a container, where water nozzles have been installed to spray the dust down the drain. This solution was one of the solutions that affected the dust the least and effectively removed the dust. It was also reasonably priced for a safe and efficient solution.
93

Effects of Dust Controls and Dust Sources on Respirable Coal Mine Dust Characteristics

Animah, Festus Ayinimi 14 October 2024 (has links)
Respirable coal mine dust (RCMD) continues to pose serious health hazards to workers. Over the past few decades, new regulations, monitoring technologies, and improved dust controls have emerged, and all are based on the presumption that limiting RCMD on the basis of mass will effectively mitigate the exposure hazards. Given the latency of exposure outcomes, it will be some time before the full impact of these strategies can be evaluated. In the meantime, there is increasing awareness that RCMD particle characteristics, in addition to mass, might be important. This dissertation comprises four separate studies which explore the effects of primary RCMD sources and/or engineering controls on particle size and constituents. To enable a direct comparison of dust generation from primary dust sources, a field study was conducted to investigate the dust generation and particle characteristics between coal and the rock strata. Results indicated that finer and more dust was generated when mining predominantly into the rock strata versus the coal strata, while the operation of a flooded bed scrubber and an increase in water sprays pressure and volume generally suppressed dust. Prior government research, conducted within the Mining Research Division of the National Institute of Occupational Safety and Health (NIOSH) evaluated the dust mass concentrations removal efficiency of different dust controls (i.e., a dry and wet scrubber, canopy air curtain, and a wet versus dry dust collection boxes). In the second and third studies, preserved samples from these prior NIOSH dust control studies were re-analyzed and evaluated to understand their effects on dust characteristics. Results indicated that the efficiency of dust controls was particle size dependent, as these controls mostly showed no appreciable effects on dust constituents. Generally, the cleaning of dust from a novel wet dust collection box versus a traditional dry dust box led to a reduction in operator exposure to hazardous dust. In the final study, a laboratory prototype flooded bed scrubber was evaluated to understand its efficiency on dust between different particle size bins (i.e., by particle count) ranging from 0.3-10 µm. From the results, removal efficiencies were generally low – and sometimes negative, for dust particles mostly in each of the size bins less than 2 µm. The results presented here highlight the need to holistically evaluate dust controls to understand their efficiency on dust of different particle sizes and constituents, so that informed decisions can be made on the best controls to adopt in mine operations. / Doctor of Philosophy / Coal production contributes significantly to steel making and electricity generation in the US. During the mining process, very fine dust is generated—called "respirable" dust— which represents a significant health hazard to workers. Indeed, many cases of occupational lung diseases linked to respirable dust have been reported over the past few decades, and disease rates remain high. Dust monitoring and control efforts are largely based on limiting the total mass of respirable dust. However, there is growing evidence that specific types of dust present disproportionate hazards—including the smallest particles, which do not contribute much to total mass, and mineral particles such as silica. The research in this dissertation explores the effects of primary dust sources and controls on respirable dust size and constituents. The major findings are as follows: when using typical equipment, mining into the rock strata that surrounds the target coal seam can generate much more dust than mining the coal itself. This dust generated can be finer and contain more mineral dust like silica and silicates. Furthermore, most dust controls used to suppress dust do not appear to be selective with respect to particle type but are generally less efficient for removing finer particles. This implies that, while dust mass removal efficiency may be high, controls might still be needed where very fine dust particles pose substantial hazards. Additionally, mine operations could develop monitoring techniques and re-orient their dust controls to target and better mitigate the most hazardous primary sources of dust such as dust from the rock strata.
94

The effect of vacuum cleaning upon household atmospheric dust

Brethour, Sylvia Gay. January 1966 (has links)
LD2668 .T4 1966 B75 / Master of Science
95

Control of rectifier equipment used for electrostatic precipitation

McLellan, P. G. January 1989 (has links)
No description available.
96

Ecology of the house dust mite Dermatophagoides pteronyssinus (Trouessart)

Hay, David B. January 1991 (has links)
No description available.
97

Studies on the use of models for the investigation of shearer drum dust generation

Bell, D. C. January 1985 (has links)
No description available.
98

A comparative study between the guinea pig and man investigating the pathogenesis of byssinosis

Griffiths-Johnson, D. A. January 1988 (has links)
No description available.
99

Dust detection systems for cometary encounter

Evans, G. C. January 1987 (has links)
No description available.
100

Cometary coma modelling in collisionless regime

Foster, M. J. January 1999 (has links)
No description available.

Page generated in 0.0883 seconds