For aluminum alloy casting, degassing is a necessary step for molten metal, which can extract the dissolved hydrogen in the melt. For copper-containing aluminum alloys, a traditional method is that using the mixed gas of inert gas and chlorine as the degassing agent. Because of the toxicity of the gaseous chlorine, the industrial is trying to avoid using it even though this method can contribute to good castings. As a potential solution, the foundry only used argon during degassing, however, the castings with this method were unacceptable since the occurrence of defects. The goal of this project is to develop a new green and clean degassing method for copper- containing alloys without the usage of gaseous chlorine. To achieve this goal, identify those defects and figure out the source of those defects are necessary. Totally four hypotheses of the occurrence of defects were supposed and two of them were discussed in this thesis. They are ineffective hydrogen removal and metal-mold reaction. Experiments were set in WPI and Palmer Foundry to investigate defects from samples with different conditions. This thesis collected and discussed the results from experiments, and made the conclusion that whether these two hypotheses contribute to the occurrence of defects.

Cyclone separators have been described in detail and, although substantial research has been performed on solid/gas devices, the use of cyclones for gas/liquid separation has been comparatively ignored; this is particularly true for higher concentrations of liquid and for degassing applications. Consequently no generic models are available which will predict separation efficiency or pressure drop for all designs of cyclone. A novel design of axial flow cyclone called WELLSEP was examined for the purpose of degassing. This design was not believed to be optimal and no design criteria or performance prediction models were available for it. An experimental programme was therefore produced and executed to investigate changes in geometry and the affect of fluid dynamics. Changes to the length, vortex finder and swirl generator were examined first and then one design was selected and tested over a number of liquid flow rates, Gas Void Fractions (GVFs) and liquid extractions. Data was collected from the experiments which assisted in the development of semi-empirical models for the prediction of pressure drop and separation efficiency. These models could be used in the design of WELLSEP. Geometric and fluid dynamics changes have both been shown to influence the performance of the tested cyclone. The principal conclusions that have been drawn from this research are: Of the tested designs, the design based upon a 30mm vortex finder diameter, settling chamber length of three times the diameter of the cyclone and a four start helix gave the optimum separation efficiency over the greatest range of conditions. The separation efficiency is affected by the superficial liquid velocity and the liquid extraction but not the GVF. The dimensionless pressure drop coefficient (Euler number) is a function of liquid extraction and GVF. It may also be a function of the superficial liquid velocity but it is unproven by this research.

No description available.

Iceland straddles the Mid-Atlantic Ridge and overlies a mantle hotspot. This tectonic setting produces voluminous tholeiitic magmas. Volcanism in Iceland is focussed along three neovolcanic spreading ridges. During the Holocene, the Eastern Volcanic Zone (EVZ) in southeast Iceland has been the most volcanically active and has been the site of several large (>6 km3) eruptions, including the only floodbasalt type eruption in recorded history, the 1783-84 Laki eruption. Three eruptions of large volume have been sampled for this study: the 1783-84 Laki eruption (15.1 km3); the 3,000-4,000 yBP Thjórsárdalur eruption (probably >4 km3); and the ~8,600 yBP Thjórsá eruption (>21 km3). The products of these eruptions have been analysed using a range of analytical techniques, with the specific aim of investigating crystallisation, degassing and mixing processes in the magma reservoirs that feed large eruptions. The Laki eruption has been the particular focus of this study. Samples from different parts of the lava flow show fine-scale variations in trace element concentrations and ratios. This compositional variation is not fully explained by fractional crystallisation processes, but is strongly controlled by crystal accumulation as whole-rock incompatible trace element concentrations show a linear, negative correlation with the mass fraction of crystals in the sample. Simple crystal accumulation models, however, fail to explain the compositional variation, and one explanation is that the homogeneous Laki melt mixed with varying proportions of a crystal mush that contained its own liquid. The results of thermobarometry calculations indicate that the erupted Laki liquid was in equilibrium with olivine, plagioclase and augite at 1-3 kb. Most of the crystals carried by the flow are too primitive to have crystallised from the erupted liquid and barometry calculations indicate that clinopyroxene crystallised at 3-7 kb. The majority of the large crystals hosted in the Laki basalt samples are therefore antecrysts that grew within the same magma plumbing system as the Laki carrier melt but are not in direct chemical equilibrium with it. This finding is verified by the fact that olivine crystals that are too magnesian to be in chemical equilibrium with the Laki whole-rock composition contain melt inclusions with average La/Yb values that are the same within error as the whole-rock values. The wide range of La/Yb values in melt inclusions hosted in the most magnesian (Fo86) olivine crystals in comparison to the least magnesian (Fo<74) indicates the initial variability of the Laki magma prior to concurrent crystallisation and extensive mixing, which acted to homogenise the carrier melt composition. The preservation of a wide range of La/Yb within the melt inclusions in comparison to the whole-rock composition, and a range of La/Yb values in different inclusions from the same crystal, indicates short timescales between melt inclusion entrapment and quenching during eruption. Melt inclusion studies also reveal the dissolved volatile content of the Laki magma at the onset of olivine crystallisation, although the majority of H2O concentrations have almost certainly been reset by low pressure diffusive exchange with the host crystal or surrounding magma. Comparison of the behaviour of volatiles with that of incompatible elements in the melt inclusions indicates that CO2 was degassing during olivine crystallisation, but S, F and Cl were not. New estimates of total volatile loading to the atmosphere during the eruption based on melt inclusion volatile concentrations show SO2 and HCl loading comparable to previous estimates, but higher HF loading. Mass balance calculations show that the observed H2O and CO2 concentrations of melt inclusions hosted in olivines in chemical equilibrium with the Laki whole-rock composition are ~50% and ~93% lower respectively than would be expected if no pre-eruptive degassing of the magma reservoir had occurred, meaning that pre-eruptive degassing of H2O and CO2 from the magma must have been significant. Lava flows from Thjórsá are more compositionally variable than those from Laki, and have different average major and trace element compositions. Compositional variation within the Thjórsá whole-rock composition is explained by a combination of source variation and fractional crystallisation, and, unlike Laki, is not strongly controlled by crystal accumulation.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: hydrogen removal; metal cleaning; particle removal. Includes bibliographical references (p. 42-43).

Volatile emissions from Cascades cinder cone eruptions have been well-documented; however the implications for understanding the effects that volcanic gases have on surrounding communities have not been addressed. This study examines the hazards from volatile degassing during explosive activity by (1) analyzing S, Cl, and F concentrations dissolved in olivine-hosted melt inclusions and matrix glass from cinder cones located in central Oregon and northern California, (2) estimating the mass of volcanic gas degassed during these eruptions, and (3) predicting gas concentrations downwind of the vent. Analyses reveal that the magmas degassed >88% S, <49% Cl, and <50% F during eruption, equating to a release of ≤4.5 Mt SO2, ≤0.2 Mt HCl, and ≤0.2 Mt HF. Predictions of gas concentrations downwind of the vent provides reassurance that the levels of volcanic gases were not high enough at the time of eruption to present acute or severe health hazards to nearby residents.

H2O and CO2 concentrations of the glass phase in melt inclusions (MI) are commonly used both as a barometer and to track magma degassing behavior during ascent due to the strong pressure dependence of H2O and CO2 solubilities in silicate melts. A requirement for this method to be valid is that the glass phase in the MI must represent the composition of the melt that was originally trapped. However, melt inclusions commonly contain a vapor bubble that formed after trapping. Such bubbles may contain CO2 that was originally dissolved in the melt. In this study, we determined the contribution of CO2 in the vapor bubble to the overall CO2 content of MI based on quantitative Raman analysis of the vapor bubbles in MI from the 1959 Kilauea Iki, 1960 Kapoho, 1974 Fuego volcano, and 1977 Seguam Island eruptions. The bubbles contain up to 90% or more of the total CO2 in some MI. Reconstructing the original CO2 content by adding the CO2 in the bubble back into the melt results in an increase in CO2 concentration by as much an order of magnitude (1000s of ppm), corresponding to trapping pressures that are significantly greater (by 1 to >3 kbars) than one would predict based on analysis of the volatiles in the glass alone. Many MI also showed the presence of a carbonate mineral phase; failure to include its contained CO2 when reconstructing the CO2 content of the originally trapped melt may introduce significant errors in the calculated volatile budget. / Master of Science

abstract: Among volcanic gases, sulfur dioxide (SO2) is by far the most commonly measured. More than a monitoring proxy for volcanic degassing, SO2 has the potential to alter climate patterns. Persistently active explosive volcanoes are characterized by short explosive bursts, which often occur at periodic intervals numerous times per day, spanning years to decades. SO2 emissions at those volcanoes are poorly constrained, in large part because the current satellite monitoring techniques are unable to detect or quantify plumes of low concentration in the troposphere. Eruption plumes also often show high concentrations of ash and/or aerosols, which further inhibit the detection methods. In this work I focus on quantifying volcanic gas emissions at persistently active explosive volcanoes and their variations over short timescales (minutes to hours), in order to document their contribution to natural SO2 flux as well as investigate the physical processes that control their behavior. In order to make these measurements, I first develop and assemble a UV ground-based instrument, and validate it against an independently measured source of SO2 at a coal-burning power plant in Arizona. I establish a measurement protocol and demonstrate that the instrument measures SO2 fluxes with < 20 % error. Using the same protocol, I establish a record of the degassing patterns at Semeru volcano (Indonesia), a volcano that has been producing cycles of repeated explosions with periods of minutes to hours for the past several decades. Semeru produces an average of 21-71 tons of SO2 per day, amounting to a yearly output of 8-26 Mt. Using the Semeru data, along with a 1-D transient numerical model of magma ascent, I test the validity of a model in which a viscous plug at the top of the conduit produces cycles of eruption and gas release. I find that it can be a valid hypothesis to explain the observed patterns of degassing at Semeru. Periodic behavior in such a system occurs for a very narrow range of conditions, for which the mass balance between magma flux and open-system gas escape repeatedly generates a viscous plug, pressurizes the magma beneath the plug, and then explosively disrupts it. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2015

La cavitation hydrodynamique, et plus particulièrement la cavitation à poche attachée, peut apparaitre et se développer dans des écoulements turbulents complexes à l’intérieur de décollements de la couche limite laminaire. Ce phénomène s’avère être également sensible aux autres gaz présents dans l’écoulement comme l’air. Pour mieux comprendre l’attachement de poches de cavitation dans des décollements laminaires et l’influence de l’air sur celles-ci, nous proposons d’étudier des écoulements laminaires décollés d’huiles silicones visqueuses, contenant une grande quantité d’air, autour d’une géométrie Venturi lisse. Dans notre étude nous observons l’apparition de plusieurs types de poches, d’air ou de vapeur, qui peuvent s’attacher dans différents décollements de l’écoulement laminaire. Le dégazage joue alors un rôle important à hautes pressions, générant des poches d’air attachées présentant des dynamiques particulièrement intéressantes.À très basses pressions, des poches de cavitations peuvent s’attacher provoquantselon la stabilité de l’écoulement une transition à un régime transitionnel laminaire/turbulent dans leurs sillage. Cette même transition peut également apparaitre de façon intermittente à plus hautes pressions dans le sillage d’une bulle d’air recirculante, caractéristique du dégazage dans les écoulement laminaires décollés. Le régime transitionnel laminaire/turbulent, beaucoup moins sensible au dégazage, est caractérisé par de la cavitation de tourbillons, générés à hautes fréquences, dans le sillage d’un bulbe de décollement laminaire “court” le long de la pente du Venturi. Le bulbe se développe jusqu’à transitionner brutalement en bulbe “long” pour une taille de poche assez élevée, on peut associer ce phénomène à la supercavitation. / Hydrodynamic cavitation, more specifically attached cavitation, can emerge et develop in complex turbulent flows within laminar boundary layer separations. This phenomenon might be extremely sensitive to the gaz content in the flow. For an easier understanding of the attachment of cavities into laminar separated flows within the influence of air content, we propose to focus our study on viscous silicon oil laminar separated flows, presenting high gas content, within a smooth Venturi geometry. In this study, the inception of several types of attached cavities, filled with air or oil vapor, can be observed into different laminar flow separations. For high pressures, the degassing phenomenon is dominant in the flow, generating attached cavities filled with air presenting interesting dynamics. For low pressures, attach vapor cavities can emerge inducing, if the flow is unstable, the transition to laminar/turbulent transitioning regime in their wake. This transition can also occurs intermittently at higher pressures in the wake of a recirculating air bubble, characteristic to degassing into laminar separated flows. The laminar/turbulent transitioning regime, less sensitive to degassing, is characterized by vortex cavitation, occurring at high frequencies, at the rear of a “short” laminar separation bubble along the divergent Venturi slope. The “short” laminar separation bubble grows until transitioning to a “long” bubble within an large attached cavity. This transition can be associate to thesupercavitation phenomenon.

The first section of this work examines melt inclusions in phenocrysts from Volcán Popocatépetl and Volcán de Colima within the Trans Mexican Volcanic Belt (TMVB). These inclusions are dacitic to rhyolitic. Trends in melt inclusion major element and water concentrations form the evolved extension of other Mexican volcanics including those presumably derived directly from primitive melts. Water concentrations in Popocatépetl and Colima melt inclusions are similar (0.3 to 3.4 weight percent Hsub2O). Melt-vapor equilibration pressures calculated from dissolved Hsub2O and COsub2 (Popocatépetl) or Hsub2O (Colima) in melt inclusions correspond to depths of entrapment of 12 km or less. Water and carbon dioxide concentrations correlate negatively with SiOsub2 and potassium. Normalized olivine-augite-quartz compositions are consistent with near cotectic crystallization under vapor-saturated conditions at pressures of 1.5 kb or less. Our results show that Popocatépetl and Colima magmas have undergone vapor-saturated crystallization during ascent in conjunction with varying degrees of mixing between degassed rhyo-dacitic and less degassed, mafic melts in the upper portions of the crust. These data suggest melt evolution occurred in conduits or inter-fingered dikes rather than a large stratified magma chamber. Part II looks at the Masaya caldera in Nicaragua. This volcano has erupted frequently in recorded history, producing lava lakes and very high gas emissions. Melt inclusions from Masaya are basaltic, with low Hsub2O (below 0.5 wt. %), low S (less than 300 ppm) and high COsub2 concentrations (up to approximately 6000 ppm). Relationships between water, sulfur, Cl and F in combination with Masaya's high COsub2 and Ba/Zr and Ba/Nb ratios suggest that Masaya has undergone a multi stage degassing process involving 1) shallow degassing, 2) recycling of magma into a deeper reservoir, and 3) fluxing of previously degassed magma with a nearly pure COsub2 vapor. Trace element signatures of melt inclusions are consistent with contributions that have been variably metasomatized by fluids generated by dehydration of subducted sediments and/or altered oceanic crust.