Modeling heat transfer in dilute two-phase flows using the Mesoscopic Eulerian Formalism

In dilute two-phase flows, accurate prediction of the temperature of the dis- persed phase can be of paramount importance. Indeed, processes such as evaporation or chemical reactions are strongly non-linear functions of heat transfer between the carrier and dispersed phases. This study is devoted to the validation of an Eulerian description of the dispersed phase –the Meso- scopic Eulerian Formalism (MEF)– in the case of non-isothermal flows. Di- rect numerical simulations using the MEF are compared to a reference La- grangian simulation for a two-dimensional non-isothermal turbulent jet laden with solid particles. The objectives of this paper are (1) to study the influ- ence of the thermal inertia of particles on their temperature distribution and (2) conduct an a posteriori validation of the MEF, which was recently ex- tended to non-isothermal flows. The focus is on the influence of additional terms in the MEF governing equations, namely heat fluxes arising from the Random Uncorrelated Motion (RUM). Results show that mean and rms of particle temperature are strongly dependent of the thermal Stokes number. The mean temperature is satisfactorily predicted by the MEF, comparing to the Lagrangian reference. Under the conditions of the present study, the RUM heat fluxes have a marginal influence on the mean particle tempera- ture. However, a significant impact was observed on the magnitude of particle temperature fluctuations. Neglecting the RUM heat fluxes leads to erroneous results while the Lagrangian statistics are recovered when it is accounted for in the regimes of low to moderate thermal Stokes number

Simulation Numérique Directe des sprays dilués anisothermes avec le Formalisme Eulérien Mésoscopique

Le contexte général de cette thèse est la Simulation Numérique Directe des écoulements diphasiques dilués anisothermes. Un accent particulier est mis sur la détermination précise de la dispersion des particules et du transfert de chaleur entre la phase porteuse et dispersée. Cette dernière est décrite à l’aide d’une approche Eulérienne aux moments : le Formalisme Eulérien Mésoscopique (FEM) [41, 123], récemment étendu aux écoulements anisothermes [78]. Le principal objectif de ce travail est de déterminer si ce formalisme est capable de prendre en compte de manière précise l’inertie dynamique et thermique des particules dans un écoulement turbulent, et particulièrement dans une configuration avec un gradient moyen. Le code de calcul utilisé est AVBP. La simulation numérique d’un spray dilué avec une approche Eulerienne soulève des questions supplémentaires sur les méthodes numériques et les modèles employés. Ainsi, les méthodes numériques spécifiques aux écoulements diphasiques implémentées dans AVBP [69, 103, 109] ont été testées et revisitées. L’objectif est de proposer une stratégie numérique précise et robuste qui résiste aux forts gradients de fraction volumique de particule provoqués par la concentration préférentielle [132], tout en limitant la diffusion numérique. Ces stratégies numériques sont comparées sur une série de cas tests de complexité croissante et des diagnostics pertinents sont proposés. Par exemple, les dissipations dues à la physique et au numérique sont extraites des simulations et quantifiées. Le cas test du tourbillon en deux dimensions chargé en particules est suggéré comme une configuration simple pour mettre en évidence l’impact de l’inertie des particules sur leur champ de concentration et pour discriminer les stratégies numériques. Une solution analytique est aussi proposée pour ce cas dans la limite des faibles nombres de Stokes. Finalement, la stratégie numérique qui couple le schéma centré d’ordre élevé TTGC et une technique de stabilisation, aussi appelée viscosité artificielle, est celle qui fournit les meilleurs résultats en terme de précision et de robustesse. Les paramètres de viscosité artificielle (c'est-à-dire les senseurs) doivent néanmoins être bien choisis. Ensuite, la question des modèles nécessaires pour d´écrire correctement la dispersion des particules dans une configuration avec un gradient moyen est abordée. Pour ce faire, un des modèles RUM (appelé AXISY-C), proposé par Masi [78] et implémenté dans AVBP par Sierra [120], est validé avec succès dans deux configurations: un jet plan diphasique anisotherme 2D et 3D. Contrairement aux anciens modèles RUM, les principales statistiques de la phase dispersée sont désormais bien prédites au centre et aux bords du jet. Finalement, l’impact de l’inertie thermique des particules sur leur température est étudié. Les résultats montrent un effet important de cette inertie sur les statistiques mettant en évidence la nécessité pour les approches numériques de prendre en compte ce phénomène. Ainsi, l’extension du FEM aux écoulements anisothermes, c’est-à-dire les flux de chaleur RUM (notés RUM HF), est implémentée dans AVBP. L’impact des RUM HF sur les statistiques de température des particules est ensuite évalué sur les configurations des jets 2D et 3D. Les champs Eulériens sont comparés à des solutions Lagrangiennes de référence calculées par B. Leveugle au CORIA et par E. Masi à l’IMFT pour les jets 2D et 3D, respectivement. Les résultats montrent que les RUM HF améliorent la prédiction des fluctuations de température mésoscopique, et dans une moindre mesure la température moyenne des particules en fonction de la configuration. Les statistiques Lagrangiennes sont retrouvées lorsque les RUM HF sont pris en compte alors que les résultats sont dégradés dans le cas contraire. ABSTRACT : This work addresses the Direct Numerical Simulation of non-isothermal turbulent flows laden with solid particles in the dilute regime. The focus is set on the accurate prediction of heat transfer between phases and of particles dispersion. The dispersed phase is described by an Eulerian approach : the Mesoscopic Eulerian Formalism [41, 123], recently extended to non-isothermal flows [78]. The main objective of this work is to assess the ability of this formalism to accurately account for both dynamic and thermal inertia of particles in turbulent sheared flows. The CFD code used in this work is AVBP. The numerical simulation of dilute sprays with an Eulerian approach calls for specific modelling and raises additional numerical issues. First, the numerical methods implemented in AVBP for two-phase flows [69, 103, 109] were tested and revisited. The objective was to propose an accurate and robust numerical strategy that withstands the steep gradients of particle volume fraction due to preferential concentration [132] with a limited numerical diffusion. These numerical strategies have been tested on a series of test cases of increasing complexity and relevant diagnostics were proposed. In particular, the two-dimensional vortex laden with solid particles was suggested as a simple configuration to illustrate the effect of particle inertia on their concentration profile and to test numerical strategies. An analytical solution was also derived in the limit of small inertia. Moreover, dissipations due to numerics and to physical effects were explicitly extracted and quantified. Eventually, the numerical strategy coupling the highorder centered scheme TTGC with a stabilization technique –the so called artificial viscosity– proved to be the most accurate and robust alternative in AVBP if an adequate set-up is used (i.e. sensors). Then, the issue of the accurate prediction of particle dispersion in configurations with a mean shear was adressed. One of the RUM model (denoted AXISY-C), proposed by Masi [78] and implemented by Sierra [120], was successfully validated in a two-dimensional and a three-dimensional non-isothermal jet laden with solid particles. Contrary to the former RUM models [63, 103], the main statistics of the dispersed phase were recovered at both the center and the edges of the jet. Finally, the impact of the thermal inertia of particles on their temperature statistics has been investigated. The results showed a strong dependency of these statistics to thermal inertia, pinpointing the necessity of the numerical approaches to account for this phenomenon. Therefore, the extension of the MEF to non isothermal conditions, i.e. the RUM heat fluxes, has been implemented in AVBP. The impact of the RUM HF terms on the temperature statistics was evaluated in both configurations of 2D and 3D jets. Eulerian solutions were compared with Lagrangian reference computations carried out by B. Leveugle at CORIA and by E. Masi at IMFT for the 2D and 3D jets, respectively. Results showed a strong positive impact of the RUM HF on the fluctuations of mesoscopic temperature, and to a lesser extent on the mean mesoscopic temperature depending of the configuration. Neglecting the RUM HF leads to erroneous results whereas the Lagrangian statistics are recovered when they are accounted for

Direct Numerical Simulation of non-isothermal dilute sprays using the Mesoscopic Eulerian Formalism

This work addresses the Direct Numerical Simulation of non-isothermal turbulent flows laden with solid particles in the dilute regime. The focus is set on the accurate prediction of heat transfer between phases and of particles dispersion. The dispersed phase is described by an Eulerian approach : the Mesoscopic Eulerian Formalism [41, 123], recently extended to non-isothermal flows [78]. The main objective of this work is to assess the ability of this formalism to accurately account for both dynamic and thermal inertia of particles in turbulent sheared flows. The CFD code used in this work is AVBP. The numerical simulation of dilute sprays with an Eulerian approach calls for specific modelling and raises additional numerical issues. First, the numerical methods implemented in AVBP for two-phase flows [69, 103, 109] were tested and revisited. The objective was to propose an accurate and robust numerical strategy that withstands the steep gradients of particle volume fraction due to preferential concentration [132] with a limited numerical diffusion. These numerical strategies have been tested on a series of test cases of increasing complexity and relevant diagnostics were proposed. In particular, the two-dimensional vortex laden with solid particles was suggested as a simple configuration to illustrate the effect of particle inertia on their concentration profile and to test numerical strategies. An analytical solution was also derived in the limit of small inertia. Moreover, dissipations due to numerics and to physical effects were explicitly extracted and quantified. Eventually, the numerical strategy coupling the highorder centered scheme TTGC with a stabilization technique –the so called artificial viscosity– proved to be the most accurate and robust alternative in AVBP if an adequate set-up is used (i.e. sensors). Then, the issue of the accurate prediction of particle dispersion in configurations with a mean shear was adressed. One of the RUM model (denoted AXISY-C), proposed by Masi [78] and implemented by Sierra [120], was successfully validated in a two-dimensional and a three-dimensional non-isothermal jet laden with solid particles. Contrary to the former RUM models [63, 103], the main statistics of the dispersed phase were recovered at both the center and the edges of the jet. Finally, the impact of the thermal inertia of particles on their temperature statistics has been investigated. The results showed a strong dependency of these statistics to thermal inertia, pinpointing the necessity of the numerical approaches to account for this phenomenon. Therefore, the extension of the MEF to non isothermal conditions, i.e. the RUM heat fluxes, has been implemented in AVBP. The impact of the RUM HF terms on the temperature statistics was evaluated in both configurations of 2D and 3D jets. Eulerian solutions were compared with Lagrangian reference computations carried out by B. Leveugle at CORIA and by E. Masi at IMFT for the 2D and 3D jets, respectively. Results showed a strong positive impact of the RUM HF on the fluctuations of mesoscopic temperature, and to a lesser extent on the mean mesoscopic temperature depending of the configuration. Neglecting the RUM HF leads to erroneous results whereas the Lagrangian statistics are recovered when they are accounted for

Feasible Metabolisms in High pH Springs of the Philippines

A field campaign targeting high pH, H2-, and CH4-emitting serpentinite-associated springs in the Zambales and Palawan Ophiolites of the Philippines was conducted in 2012-2013, and enabled description of several springs sourced in altered pillow basalts, gabbros, and peridotites. We combine field observations of pH, temperature, conductivity, dissolved oxygen, and oxidation-reduction potential with analyses of major ions, dissolved inorganic carbon, dissolved organic carbon, and dissolved gas phases in order to model the activities of selected phases important to microbial metabolism, and to rank feasible metabolic reactions based on energy yield. We document changing geochemical inventories in these springs between sampling years, and examine how the environment supports or prevents the function of certain microbial metabolisms. In all, this geochemistry-based assessment of feasible metabolisms indicates methane cycling, hydrogen oxidation, some iron and sulfur metabolisms, and ammonia oxidation are feasible reactions in this continental site of serpentinization

Internal and Tectonic Evolution of Mercury

Mercury's geological and internal evolution presents an interesting enigma: are there conditions that allow for both apparently limited radial contraction over the last 4 billion years and sufficiently rapid core cooling at present to permit a hydromagnetic dynamo? To address this question, we simulate the coupled thermal, magmatic, and tectonic evolution of Mercury for a range of parameters (e.g., mantle rheology, internal heat production, core sulfur content) in order to outline the set of assumptions most consistent with these two conditions. We find that among the models tested, the only ones strictly consistent with ∼1-2 km of radial contraction since 4 Ga and a modern magnetic field generated by a core dynamo are those with a dry-olivine mantle rheology, heat production provided primarily by Th (negligible U or K), and a bulk core sulfur content >6.5 wt%. However, because of the limited coverage and resolution of Mariner 10 imaging and derived topography, the tectonic history of an entire hemisphere is unknown. The potential for other mechanisms (e.g., long-wavelength lithospheric folds) to accommodate contraction remains untested, limiting the ability to restrict models on the basis of accumulated strain. Furthermore, Mercury's magnetic field may be a consequence of a thermoelectric dynamo or even crustal remanence; neither hypothesis places strong constraints on current heat flux from the core. Spacecraft observations of Mercury are needed to elucidate further the internal structure and evolution of the planet

Out of the Dark: Transitional Subsurface-to-Surface Microbial Diversity in a Terrestrial Serpentinizing Seep (Manleluag, Pangasinan, the Philippines)

In the Zambales ophiolite range, terrestrial serpentinizing fluid seeps host diverse microbial assemblages. The fluids fall within the profile of Ca2+-OH−-type waters, indicative of active serpentinization, and are low in dissolved inorganic carbon (DIC) (\u3c0.5 ppm). Influx of atmospheric carbon dioxide (CO2) affects the solubility of calcium carbonate as distance from the source increases, triggering the formation of meter-scale travertine terraces. Samples were collected at the source and along the outflow channel to determine subsurface microbial community response to surface exposure. DNA was extracted and submitted for high-throughput 16S rRNA gene sequencing on the Illumina MiSeq platform. Taxonomic assignment of the sequence data indicates that 8.1% of the total sequence reads at the source of the seep affiliate with the genus Methanobacterium. Other major classes detected at the source include anaerobic taxa such as Bacteroidetes (40.7% of total sequence reads) and Firmicutes (19.1% of total reads). Hydrogenophaga spp. increase in relative abundance as redox potential increases. At the carbonate terrace, 45% of sequence reads affiliate with Meiothermus spp. Taxonomic observations and geochemical data suggest that several putative metabolisms may be favorable, including hydrogen oxidation, H2-associated sulfur cycling, methanogenesis, methanotrophy, nitrogen fixation, ammonia oxidation, denitrification, nitrate respiration, methylotrophy, carbon monoxide respiration, and ferrous iron oxidation, based on capabilities of nearest known neighbors. Scanning electron microscopy and energy dispersive X-ray spectroscopy suggest that microbial activity produces chemical and physical traces in the precipitated carbonates forming downstream of the seep\u27s source. These data provide context for future serpentinizing seep ecosystem studies, particularly with regards to tropical biomes

High pH Microbial Ecosystems in a Newly Discovered, Ephemeral, Serpentinizing Fluid Seep at Yanartaş (Chimera), Turkey

Gas seeps emanating from Yanartaş (Chimera), Turkey, have been documented for thousands of years. Active serpentinization produces hydrogen and a range of carbon gases that may provide fuel for life. Here we report a newly discovered, ephemeral fluid seep emanating from a small gas vent at Yanartaş. Fluids and biofilms were sampled at the source and points downstream. We describe site conditions, and provide microbiological data in the form of enrichment cultures, Scanning electron microscopy (SEM), carbon and nitrogen isotopic composition of solids, and PCR screens of nitrogen cycle genes. Source fluids are pH 11.95, with a Ca:Mg of ~200, and sediments under the ignited gas seep measure 60°C. Collectively, these data suggest the fluid is the product of active serpentinization at depth. Source sediments are primarily calcite and alteration products (chlorite and montmorillonite). Downstream, biofilms are mixed with montmorillonite. SEM shows biofilms distributed homogeneously with carbonates. Organic carbon accounts for 60% of the total carbon at the source, decreasing downstream to \u3c15% as inorganic carbon precipitates. δ13C ratios of the organic carbon fraction of solids are depleted (−25 to −28‰) relative to the carbonates (−11 to −20‰). We conclude that heterotrophic processes are dominant throughout the surface ecosystem, and carbon fixation may be key down channel. δ15N ratios ~3‰, and absence of nifH in extracted DNA suggest that nitrogen fixation is not occurring in sediments. However, the presence of narG and nirS at most locations and in enrichments indicates genomic potential for nitrate and nitrite reduction. This small seep with shallow run-off is likely ephemeral, but abundant preserved microterracettes in the outflow and the surrounding area suggest it has been present for some time. This site and others like it present an opportunity for investigations of preserved deep biosphere signatures, and subsurface-surface interactions

High pH microbial ecosystems in a newly discovered, ephemeral, serpentinizing fluid seep at YanartaÅŸ (Chimera), Turkey

Gas seeps emanating from ophiolites at Yanartaş (Chimaera), Turkey, have been documented for thousands of years. Active serpentinization produces hydrogen and a range of carbon gases that may provide fuel for life. Here we report a newly discovered, ephemeral fluid seep emanating from a small gas vent at Yanartaş. Fluids and biofilms were sampled at the source and points downstream. We describe site conditions, and provide microbiological data in the form of enrichment cultures, scanning electron microscopy (SEM), carbon and nitrogen isotopic composition of solids, and PCR screens of nitrogen cycle genes. Source fluids are pH 11.95, with a Ca:Mg of ~200, and sediments under the ignited gas seep measure 60°C. Collectively, these data suggest the fluid is the product of active serpentinization at depth. Source sediments are primarily calcite and alteration products (chlorite and montmorillonite). Downstream, biofilms are mixed with montmorillonite. SEM shows biofilms distributed homogeneously with carbonates. Organic carbon accounts for 60% of the total carbon at the source, decreasing downstream to <15% as inorganic carbon precipitates. δ13C ratios of the organic carbon fraction of solids are depleted (−25 to −28 ‰) relative to the carbonates (−11 to −20‰). We conclude that heterotrophic processes are dominant throughout the surface ecosystem, and carbon fixation may be key down channel. δ15N ratios ~ 3‰, and absence of nifH in extracted DNA suggest that nitrogen fixation is not occurring in sediments. However, the presence of narG and nirS at most locations and in enrichments indicates genomic potential for nitrate and nitrite reduction. This small seep with shallow run-off is likely ephemeral, but abundant preserved microterracettes in the outflow and the surrounding area suggest it has been present for some time. This site and others like it present an opportunity for investigations of preserved deep biosphere signatures, and subsurface-surface interactions