Interstitial Gases Research Articles

Experimental and numerical study of conductive heat transfer in aggregate particles using a flighted, rotary drum

Heating aggregates and recycled materials is an energy intensive part of the process of producing asphalt pavement. Sustainability can be improved by increasing the portion of recycled materials while decreasing the energy required to produce the asphalt mixture. A common method to incorporate recycled materials is to mix heated aggregate with cold recycled materials. Interstitial gas conduction is the dominant mode of heat transfer in this process due to the low thermal conductivity of these materials. In this study, a particle-based model that includes the contribution of the interstitial gases was validated with a novel experimental method using infrared (IR) thermography to track the temperature evolution of a mixture of hot and cold aggregates in a flighted, inclined drum. The simulation results showed good agreement with the experiment demonstrating the model’s ability to capture the heat transfer and the particle flow in the dynamic system of irregular shaped particles.

Volatile organic compounds (VOCs) from diffuse degassing areas: Interstitial soil gases as message bearers from deep hydrothermal reservoirs

The chemical composition of volatile organic compounds (VOCs) in interstitial soil gases from hydrothermal areas is commonly shaped by both deep hydrothermal conditions (e.g., temperature, redox, sulfur fugacity) and shallow secondary processes occurring near the soil-atmosphere interface. Caldara di Manziana and Solfatara di Nepi, i.e., two hydrothermal systems characterized by diverse physicochemical conditions located in the Sabatini Volcanic District and Vicano-Cimino Volcanic District, respectively (Central Italy), were investigated to evaluate the capability of VOCs in soil gases to preserve information from the respective feeding deep fluid reservoirs. Hierarchical cluster analyses and robust principal component analyses allowed recognition of distinct groups of chemical parameters of soil gases collected from the two study areas. The compositional dissimilarities from the free-gas discharges were indeed reflected by the chemical features of soil gases collected from each site, despite the occurrence of shallow processes, e.g., air mixing and microbial degradation processes, affecting VOCs. Four distinct groups of VOCs were recognized suggesting similar sources and/or geochemical behaviors, as follows: (i) S-bearing compounds, whose abundance (in particular that of thiophenes) was strictly dependent on the sulfur fugacity in the feeding system; (ii) C4,5,7+ alkanes, n-hexane, cyclics and alkylated aromatics, related to relatively low-temperature conditions at the gas source; (iii) C2,3 alkanes, benzene, benzaldehyde and phenol, i.e., stable compounds and thermal degradation products; and (iv) aliphatic O-bearing compounds, largely influenced by shallow processes within the soil. However, they maintain a chemical speciation that preserves a signature derived from the supplying deep-fluids, with aldehydes and ketones becoming more enriched after intense interaction of the hypogenic fluids with shallow aquifers. Accordingly, the empirical results of this study suggest that the chemical composition of VOCs in soil gases from hydrothermal areas provides insights into both deep source conditions and fluid circulation dynamics, identifying VOCs as promising geochemical tracers for geothermal exploration.

Experimental validation of a particle-based method for heat transfer incorporating interstitial gas conduction in dense granular flow using a rotary drum

Conductive heat transfer in granular material is important in many industrial processes. For dense systems where the materials have low thermal conductivity, much of the heat transfer will occur through interstitial gases. Industry requires flexible and efficient computational methods to capture these phenomena at scale. In this study, a recently proposed particle-based model that includes the contribution of the interstitial gases was validated using an experiment. This model was originally derived from a multi-scale analysis of static, random packings. To test this approach in dense, dynamic systems, the model results were compared to experimental data for glass beads in an indirectly heated rotating drum. Infrared (IR) thermography was used to track the temperature evolution of the glass beads and the drum wall temperature. Discrete element simulations were performed with the experimental wall temperature used as a transient wall boundary condition. Results from the simulation show good agreement with the experimental data both for the bulk average temperature and for the bed profile, demonstrating the model’s ability to capture the gas contribution in dynamic systems.

Doubled J c of Bi2Sr2CaCu2O x wires by partial melting and recrystallization heat treatment under 10 bar after vacuum degassing of the precursor powder and pre-densifying of the wires

Final heat treatment involving partial melting and recrystallization under a high pressure of 50–100 bar is not conducive to the preparation of Bi2Sr2CaCu2O x (Bi2212) magnets; it also greatly increases the cost of research into Bi2212 wires. To solve these problems, in this work a final heat treatment under 10 bar was used to prepare Bi2212 wires with a high bulk density and high critical current density (J c). The ambient pressure of the final heat treatment in this paper is only one-fifth of that of the traditional overpressure for final heat treatment of Bi2212 wires. The J c of the wires is more than 2.4 times higher than that of Bi2212 wires with a final heat treatment at 1 bar and is consistent with that of samples having a final heat treatment at the traditional 50–100 bar. The reason why the ambient pressure of the final heat treatment can be greatly reduced in this work is: (a) vacuum degassing of the precursor powder eliminated the adsorption and interstitial impurity gases in the long Bi2212 wires, and reduced the internal gas pressure of the wires; (b) pre-treatment at 800 °C and 250 bar compressed the Bi2212 wires to their full density. Thus, during the subsequent final heat treatment, the low ambient pressure of 10 bar can overcome the difference between the residual gas pressure inside the wires and the yield strength or creep strength of the Ag sheath, and prevent expansion of the internal gas in the wires, so that the Bi2212 wires are always close to full density. The ambient pressure of the final heat treatment in this paper needs to prevent the expansion of the Bi2212 wires not compress them, so the pressure can be very low. The 10 bar low pressure final heat treatment will solve the problems of the high cost of research into Bi2212 wires and the difficult overpressure heat treatment of Bi2212 magnets.

Numerical and experimental investigation of the effect of interstitial gases on conductive heat transfer for dense particulate systems

Many industrial processes involve granular heat transfer. Within these processes are a sub-set of applications where the particles are densely packed and the surrounding gas is predominantly stagnant. For materials with low thermal conductivity much of the heat transfer will occur through the interstitial gases so capturing this effect is critical to represent these systems numerically. Resolving the gas phase explicitly using a fluid solver and coupling to a particle method is possible but computationally expensive. Higher fidelity models often make simulation of applications at the industrial scale intractable. With this in mind we seek a numerical method that captures the important heat transfer phenomena in dense granular systems with minimal additional computational effort. In this work we first characterize one common particle based approach proposed by Rong and Horio that calculates the contribution through a stagnant gas film surrounding each particle. We compare this approach to fluid simulations of a particle-wall and a particle-particle collision to evaluate the validity of the underlying assumptions of the Rong and Horio model. We then use a multi-scale approach to examine the relationship between the local packing structure and the contribution of the interstitial gas. From this we propose a new dimensionless parameter that permits the inclusion of the gas effect in a particle based simulation method with minimal additional computational effort and without explicitly having to include the gas phase. The model is then validated against a static experiment and compared with the Rong and Horio model.

Total CO2 output and carbon origin discharged from Rincón de Parangueo Maar (México)

A geochemical survey was carried out (May 2016) in the Rincón de Parangueo maar in Valle de Santiago, México. The challenge was to measure CO2 and CH4 fluxes discharged from soil and to investigate the chemical and isotopic compositions of interstitial soil gases and remaining vents at the bottom of maars system subjected to critical and high rate drawdown aquifer. Total CO2 flux calculated by sequential Gaussian simulation is 10.6 ton d−1 (±2.1 ton d−1) over the entire crater maar area. Two degassing groups were recognized: Group A (background degassing) with values lower than 10 g m−2 d−1 (40% of the total measurements) and Group B with values ranging between 10 and 347.1 g m−2 d−1 (60% of the total amount of measurements). CH4 flux ranges from 2.1 to 1577 g m−2 d−1. CH4/CO2 flux mean ratio is ~20.51 while CH4/CO2 concentration ratios are 78 and 119 for bubbling gases and 8.4 for interstitial gases. The δ13C-CH4 values are ~65 per mil vs V-PDB indicating a biogenic origin of methane in bubbling and interstitial gases. The δ13C-CO2 values, ranging from −10.6 to −27.6 and −1.9 per mil vs V-PDB for bubbling gases and the interstitial gases, respectively, suggest secondary CO2 consumption within the soil.

Carbon isotopic signature of interstitial soil gases reveals the potential role of ecosystems in mitigating geogenic greenhouse gas emissions: Case studies from hydrothermal systems in Italy

Volcanic and hydrothermal areas largely contribute to the natural emission of greenhouse gases to the atmosphere, although large uncertainties in estimating their global output still remain. Nevertheless, CO2 and CH4 discharged from hydrothermal fluid reservoirs may support active soil microbial communities. Such secondary processes can control and reduce the flux of these gases to the atmosphere. In order to evaluate the effects deriving from the presence of microbial activity, chemical and carbon (in CO2 and CH4) isotopic composition of interstitial soil gases, as well as diffuse CO2 fluxes, of three hydrothermal systems from Italy were investigated, i.e. (i) Solfatara crater (Campi Flegrei), (ii) Monterotondo Marittimo (Larderello geothermal field) and (iii) Baia di Levante in Vulcano Island (Aeolian Archipelago), where soil CO2 fluxes up to 2400, 1920 and 346 g m−2 day−1 were measured, respectively. Despite the large supply of hydrothermal fluids, 13CO2 enrichments were observed in interstitial soil gases with respect to the fumarolic gas discharges, pointing to the occurrence of autotrophic CO2 fixation processes during the migration of deep-sourced fluids towards the soil-air interface. On the other hand, (i) the δ13C-CH4 values (up to ~48‰ vs. V-PDB higher than those measured at the fumarolic emissions) of the interstitial soil gases and (ii) the comparison of the CO2/CH4 ratios between soil gases and fumarolic emissions suggested that the deep-sourced CH4 was partly consumed by methanotrophic activity, as supported by isotope fractionation modeling. These findings confirmed the key role that methanotrophs play in mitigating the release of geogenic greenhouse gases from volcanic and hydrothermal environments.

Microbiome profiling in extremely acidic soils affected by hydrothermal fluids: the case of the Solfatara Crater (Campi Flegrei, southern Italy).

An integrated geochemical and microbiological investigation of soils from the Solfatara Crater (Campi Flegrei, southern Italy) demonstrated that interstitial soil gases dominated by CO2 and other typical hydrothermal gaseous species (e.g. H2S, CH4, ethane, benzene, alkenes and S-bearing organic compounds) influenced the composition of microbial communities. The relatively high concentrations of hydrothermal fluids permeating the soil produced acidic conditions and whitish deposits that characterize the Solfatara Crater floor. Archaea and Bacteria showed almost equal cell abundance (up to 3.2×107 and 4.2×107 cell/g, respectively) with relatively low levels of biodiversity and equitability in sites characterized by elevated temperatures (up to 70°C), very low pH values (up to 2.2) and reducing conditions. In these sites, high-throughput sequencing showed the marked selection of microorganisms, mainly affiliated with the genera Thermoplasma, Ferroplasma and Acidithiobacillus. A relatively high biodiversity and concomitant distinctive structure of the microbial community were observed in soils poorly affected by fumarolic emissions that were oxic and rich in organic matter.

Active hydrothermal fluids circulation triggering small-scale collapse events: the case of the 2001–2002 fissure in the Lakki Plain (Nisyros Island, Aegean Sea, Greece)

In 2001–2002, two ground collapses occurred in the island of Nisyros (Aegean Sea, Greece), which formed a 600 m long and up to 5 m wide fissure in the vegetated central part of the Lakki Plain caldera. The fissure was alternatively ascribed to tensional stress release and hydrothermal alteration. In this study, we present original data of diffuse CO2 soil fluxes, soil temperatures, mineralogical and chemical composition of the caldera-filling deposits exposed on the fissure walls, and chemical and isotopic composition of interstitial soil gases collected from: the bottom of the fissure, the adjacent vegetated areas, the hydrothermal craters, and selected sites outside the caldera. The occurrence of intense hydrothermal alteration was shown by both mineralogical and chemical analyses of the fissure walls material. Typical mineral assemblage and enrichments in incompatible elements related to advanced argillic alteration, characterizing steam-heated hydrothermal environments, were recognized. Although the low-permeable sediment cover in the Lakki Plain concealed the underneath hydrothermal gas flow, preventing anomalous soil temperatures and CO2 fluxes, the chemical and isotopic composition of the interstitial soil gases revealed an active hydrothermal fluids circulation below the collapsed area, likely controlled by buried structural lineaments. Hydrothermal alteration can then be invoked as the most likely trigger mechanism for the 2001–2002 collapse event.

Evaluation of Near-Surface Gases in Marine Sediments to Assess Subsurface Petroleum Gas Generation and Entrapment

Gases contained within near-surface marine sediments can be derived from multiple sources: shallow microbial activity, thermal cracking of organic matter and inorganic materials, or magmatic-mantle degassing. Each origin will display a distinctive hydrocarbon and non-hydrocarbon composition as well as compound-specific isotope signature and thus the interpretation of origin should be relatively straightforward. Unfortunately, this is not always the case due to in situ microbial alteration, non-equilibrium phase partitioning, mixing, and fractionation related to the gas extraction method. Sediment gases can reside in the interstitial spaces, bound to mineral or organic surfaces and/or entrapped in carbonate inclusions. The interstitial sediment gases are contained within the sediment pore space, either dissolved in the pore waters (solute) or as free (vapour) gas. The bound gases are believed to be attached to organic and/or mineral surfaces, entrapped in structured water or entrapped in authigenic carbonate inclusions. The purpose of this paper is to provide a review of the gas types found within shallow marine sediments and examine issues related to gas sampling and extraction. In addition, the paper will discuss how to recognise mixing, alteration and fractionation issues to best interpret the seabed geochemical results and determine gas origin to assess subsurface petroleum gas generation and entrapment.

Measurements of thermal properties of icy Mars regolith analogs

In a series of laboratory experiments, we measure thermal diffusivity, thermal conductivity, and heat capacity of icy regolith created by vapor deposition of water below its triple point and in a low pressure atmosphere. We find that an ice‐regolith mixture prepared in this manner, which may be common on Mars, and potentially also present on the Moon, Mercury, comets and other bodies, has a thermal conductivity that increases approximately linearly with ice content. This trend differs substantially from thermal property models based of preferential formation of ice at grain contacts previously applied to both terrestrial and non‐terrestrial subsurface ice. We describe the observed microphysical structure of ice responsible for these thermal properties, which displaces interstitial gases, traps bubbles, exhibits anisotropic growth, and bridges non‐neighboring grains. We also consider the applicability of these measurements to subsurface ice on Mars and other solar system bodies.

Experimental study of the influences of degraded vacuum on multilayer insulation blankets

The paper presented experimental investigation on the heat transfer of MLI with different rarefied gases at different pressures. The investigations were carried out using an innovative static liquid nitrogen boil-off rate measurement system in the case of the small temperature perturbations of cold and warm boundaries. The heat fluxes for a number of inert and some polyatomic gases have been analyzed at different heat transfer conditions ranging from molecular to continuum regime, apparent thermal conductivities of the multilayer insulation were measured over a wide range of temperature (77 K–300 K) and pressure (10 −3–10 5 Pa) using the apparatus. The experimental results indicated that under degraded vacuum condition, the influences of rarefied gas on the MLI thermal performance very depend on the gas rarefaction degree which impacted by the MLI vacuum degree. Under the condition of molecular regime heat transfer, the MLI thermal performance was greatly influenced by gas energy accommodation coefficients (EAC), when under the continuum regime, the performances depend on the thermal conductivity of rarefied gas itself. Compared to the results of N 2, Ar, CO 2, Air and He as interstitial gases in the MLI, Ar was the better selection as space gas because of its low EAC and thermal conductivity characteristics on the different vacuum condition ranging from high pressure to vacuum. So different residual gases can be utilized according to the vacuum level and gas energy accommodation coefficient, in order to improve the insulation performance of low vacuum MLI.

Degradation of C 2–C 15 volatile organic compounds in a landfill cover soil

The composition of non-methane volatile organic compounds (hereafter VOCs) in i) the cover soil, at depths of 30, 50 and 70 cm, and ii) gas recovery wells from Case Passerini landfill site, (Florence, Italy) was determined by GC-MS. The study, based on the analysis of interstitial gases sampled along vertical profiles within the cover soil, was aimed to investigate the VOC behaviour as biogas transits from a reducing to a relatively more oxidizing environment. A total of 48 and 63 different VOCs were identified in the soil and well gases, respectively. Aromatics represent the dominant group (71.5% of total VOC) in soil gases, followed by alkanes (6.8%), ketones (5.7%), organic acids (5.2%), aldehydes (3.0%), esters (2.6%), halogenated compounds (2.1%) and terpenes (1.3%). Cyclics, heterocyclics, S-bearing compounds and phenols are ≤ 1%. In the wells the VOC composition is characterized by higher concentrations of cyclic (7.6%) and S-bearing compounds (2%) and lower concentrations of O-bearing compounds. The vertical distribution of VOCs in the cover soil shows significant variations: alkanes, aromatics and cyclics decrease at decreasing depth, whereas an inverse trend is displayed by the O-bearing species. Total VOC and CH 4 concentrations at a depth of 30 cm in the soil are comparable, inferring that microbial activity is likely affecting VOCs at a very minor extent with respect to CH 4. According to these considerations, to assess the biogas emission impact, usually carried out on the sole basis of CO 2 and CH 4 emission rates, the physical–chemical behaviour of VOCs in the cover soil, regulating the discharge of these highly contaminant compounds in ambient air, has to be taken into account. The soil vertical distribution of these species can be used to better evaluate the efficiency of oxidative capability of intermediate and final covers.

Heat transfer in rotary kilns with interstitial gases

While slow granular flows have been an area of active research in recent years, heat transfer in flowing particulate systems has received relatively little attention. We employ a computational technique that couples the discrete element method (DEM), computational fluid dynamics (CFD), and heat transfer calculations to simulate realistic heat transfer in a rotary kiln. To maintain simplicity, while simulating the cylindrical kiln, we use a non-uniform grid in our code. Different materials, particle sizes, and rotation speeds are used to track the transition from convection-dominated heat transfer to conduction-dominated heat transfer. At low particle conductivities, the heat transfer is dominated by gas–solid conduction; however, at higher particle conductivities solid–solid conduction plays a more important role. Moreover, our results suggest that the rate of change of the average bed temperature can display a transition as the conductivity of the interstitial medium is increased. At low interstitial transport rates, such as in vacuum, high conductivity, high heat capacity particles get heated most rapidly, but with increased interstitial transport coefficients, lower heat capacity material may get heated faster despite lower values of conductivity.

Thermal Joint Resistances of Conforming Rough Surfaces with Gas Filled Caps

An approximate analytical model is developed for predicting the heat transfer of interstitial gases in the gap between conforming rough contacts. A simple relationship for the gap thermal resistance is derived by assuming that the contacting surfaces are of uniform temperature and that the gap heat transfer area and the apparent contact area are identical. The model covers the four regimes of gas heat conduction modes, that is, continuum, temperature jump or slip, transition, and free molecular. Effects of main input parameters on the gap and joint thermal resistances are investigated. The model is compared with other models and with more than 510 experimental data points in the open literature. Good agreement is shown over the entire range of the comparison. Nomenclature A = area, m 2 a = radius of contact, m bL = specimens radius, m c1 =V ickers microhardness coefficient, Pa c2 =V ickers microhardness coefficient d = distance between two parallel plates, m F =e xternal force, N Hmic = microhardness, Pa H � = c1(1.62σ � /m) c2 ,P a H ∗ = c1(σ � /m) c2 ,P a Kn = Knudsen number k = thermal conductivity, W/mK l = depth, m M =g as parameter, m Mg = molecular weight of gas, kg/kmol Ms = molecular weight of solid, kg/kmol m = mean absolute surface slope ns = number of microcontacts P = pressure, Pa Pr = Prandtl number Q = heat flow rate, W q = heat flux, W/m 2 R = thermal resistance, K/W r, z =c ylindrical coordinates T = temperature, K t = dummy variable Y = mean surface plane separation, m z = surface height, m αT = thermal accommodation coefficient γ = ratio of gas specific heats � = mean free path, m λ = nondimensional separation ≡ Y √ 2σ

V-alloy embrittlement by irradiation in a cooling gas environment

Sub-sized tensile and Charpy specimens of the vanadium-alloy V–4Cr–4Ti have been irradiated in a piggy-back experiment with ferritic–martensitic material in the HFR at Petten at 250–450°C to about 2.5 dpa, and subsequently tested. A complex set of post-irradiation mechanical properties was found. Impact measurements showed severe shifts in ductile–brittle transition temperatures (DBTT) regardless of irradiation temperature and no clear trends of recovery at higher irradiation temperatures. The fracture surfaces always indicated transcrystalline crack propagation. Tensile tests generally revealed irradiation hardening with a maximum around 300°C, accompanied by total elongations which increased with increasing temperature. Extremely small uniform elongations at the lower temperatures suggest high localized plastic deformation under small strain rates. Deviations from expected irradiation effects led to a scrutiny of the atmospheric conditions during irradiation which revealed that the capsule had several times been flushed with He and Ne containing traces of interstitial gases or N2 for temperature adjustment. A skin was found on the specimens irradiated at the highest temperatures. X-ray diffraction results showed an uptake of nitrogen, whereas microprobe analysis suggested the presence of oxygen in the bulk. The limited data allow only a qualitative discrimination between chemical and irradiation effects.

Gap conductance in contact heat transfer

At low contact pressures, conduction across the gas gap is the predominant mode of heat transfer in a joint. Experimental results are presented for the solid spot and the gap conductance for a range of surface finishes and several interstitial gases and gas mixtures. The mean separation distance is then estimated as the difference between the effectiive gap thickness and the temperature jump distance. It is seen that a simple relation exists between the mean separation distance and surface roughness for all the gases and gas mixtures. This correlation satisfies 85% of data points to within ±4%.

Scavenging of acidic gases (HCOOH, CH3COOH, HNO3, HCl, and SO2) and ammonia in mixed liquid‐solid water clouds at the Puy de Dôme mountain (France)

In order to study scavenging processes of chemical species in mixed phase clouds, in‐cloud field measurements were conducted in December 1997 at the Puy de Dôme mountain (center of France, 1465 m above sea level). Soluble species including NH+4, Cl−;, NO3−3, SO−4, HCOO−, CH3COO−, and C2O−4 present in the different phases (supercooled water droplets, rimed snowflakes, interstitial gases, and aerosols) of cold clouds have been investigated. Conducted in parallel to microphysical studies of clouds (liquid water and ice contents, and size distribution of hydrometeors), these chemical investigations allow us to examine the partitioning of strong (HNO3 and HCl) and weak (SO2, HCOOH, and CH3COOH) acids as well as ammonia between interstitial air and the condensed phases (liquid and solid water particles) in mixed clouds present during winter at midlatitude regions. From that, we discuss the processes by which these key atmospheric species are taken up from the gas phase by the condensed phases (liquid and ice) in these cold clouds. We examine several factors which are of importance in driving the final composition of cloud ice. They include the partitioning of species between gaseous and supercooled liquid phases, the amount of rimed ice collected by snowflakes, and the retention of gas during shock freezing of supercooled droplets onto ice particles. Strong acids (HCl and HNO3) as well as NH3, being sufficiently soluble in water, are mainly partitioned into supercooled water droplets. Furthermore, being subsaturated in liquid droplets, these species are well retained in rimed ice. For these species, riming is found to be the main process driving the final composition of snowflakes, direct incorporation from the gas phase during growth of snowflakes remaining insignificant because of low concentrations in the gas phase. For light carboxylic acids the riming process mainly determines the composition of the snowflakes, but an additional significant contribution by gas incorporation during the growth of snowflakes cannot be excluded. SO2 is also present at significant levels in the interstitial air and is poorly retained in ice during riming of supercooled water droplets. However, hydroxymethanesulfonate (HMSA) was likely present in supercooled liquid droplets, making it difficult to evaluate by which mechanism S(IV) (i.e., HMSA plus SO2) has been incorporated into snowflakes.

Light hydrocarbon gases in shallow sediments in the northern North Sea

Large amounts of data on hydrocarbons in shallow marine sediments (0–6 m below sea floor) have been gathered on the Norwegian sector in conjunction with surface exploration for petroleum seepage. In this paper some results from a re-investigation of five surveys is presented. The surveys include a total of 2136 shallow cores and cover mainly the Stord Basin and the Viking Graben areas offshore Western Norway. Adsorbed gases, interstitial gases, headspace gases, grain size, and inductively coupled argon plasma elemental data have been investigated (Table 1). The adsorbed methane ranges from 10 to 5000 ppb. It has a uni-modal distribution with a median concentration of 504 ppb (weight/weight). The interstitial methane ranges from less than 1 to 500 ppb. It has a uni-modal distribution with a median concentration of 13.4 ppb. There are two classes of headspace methane samples. A “normal” class comprising about 90% of the samples lies in the range 0.1 to 500 ppb with a median of 2.1 ppb. The second class lies in the range 500 to more than 100,000 ppb with a median of 6990 ppb. The ratio of unsaturated to saturated alkane homologues in the interstitial and headspace gasses is on average equal to one and show positive correlation. This rules out thermogenic hydrocarbons as a direct source for the headspace and interstitial gasses. The proportion of unsaturated hydrocarbons in the adsorbed gas is much lower (< 1%), but also here a significant positive correlation between unsaturated and saturated alkanes is observed. The highest interstitial methane contents are found in sediments with high contents of coarse material. Principal component analysis show that the yields, dryness, and isotopic composition of adsorbed methane correlate positively with the contents of calcium and strontium, the Sr/Ca ratio in the sediments and the proportion of silt size material in the sediments. We infer from this that a major component in the adsorbed gas is cogenetic with carbonates in the fine fraction, probably resulting from in situ bacterial degradation of organic matter. Distinct and unquestionable regional headspace gas anomalies are found within the Quaternary Kleppe Senior (KSE) formation of soft, silty marine/glaciomarine clays. Outside of KSE only background levels of headspace methane is observed. Some of the most prominent headspace gas anomalies correlate very well with a shallow gas accumulation in a sand body just 10–20 m below sea floor. We conclude that gas found at the surface has migrated upwards from this sand body. The 1/3C 1/2C isotopic ratio for the anomalous methane (−51 to −100) ppt and its extremely dry characteristics are typical for a biogenic origin. We speculate that shallow biogenic gas may be a secondary form of carbon related to leakage from petroleum deposits at depth in this very prolific area.

Parametric studies of dynamic powder consolidation using a particle-level numerical model

A numerical simulation approach is used to investigate various aspects of dynamic metal powder consolidation. A two-dimensional continuum model is employed where only a few powder particles, and the interparticle voids, are considered. Consolidation is achieved by introducing large compressive stress waves in type 304 stainless-steel powder material using a high-velocity flyer plate. The effects of stress-wave amplitude on the particle deformation, consolidation rate, and temperature field are discussed based on the results of simulations using projectile impact velocities of 0.5, 1.0, and 2.0 km/s. It is demonstrated that increases in stress-wave amplitude result in higher surface temperatures leading to more extensive interparticle bonding. The 0.5 km/s impact results in full densification but is insufficient to create particle melting and bonding; the 2.0 km/s impact results in extensive interparticle melting. The effects of simple variations in the initial particle geometry are investigated by considering monosized and bimodal particle distributions and a matrix of identical hollow particles. Because each of these simulations correspond to a different initial density, the results are used to examine the effects of initial void fraction on energy deposition in the powder material during consolidation. It is shown that the average internal energy of the consolidated particles increases substantially as the initial void fraction is increased. In a final simulation, argon is placed in the regions between particles to investigate the effects of interstitial gases on the temperature field during consolidation. Shock compression of the gas results in increased surface temperatures and more extensive interparticle melting; for the materials and consolidation conditions considered, however, it is not a predominant energy deposition mechanism.