Edge Of Chamber Research Articles

Solidification and crystal growth of highly compressed hydrogen and deuterium: Time-resolved study under ramp compression in dynamic-diamond anvil cell

Solidification of hydrogen and deuterium has been studied under dynamic compression using dynamic-diamond anvil cell, time-resolved Raman spectroscopy, and fast micro-photography. Liquid H2 or D2 solidifies into a grain boundary free crystal grown from the outer edge of the sample chamber in 1–30 ms depending on the compression rate. The time scale of solidification agrees well with that of the discontinuous Raman shift across the liquid/solid phase boundary, underscoring a compression rate dependence of the solidification process. The crystal growth rates were measured to be 0.12–0.80 cm/s for H2 and 0.13–1.27 cm/s for D2, varying linearly with the compression rate.

EFFECT OF THE VIBRATION PARAMETERS ON THE ULTRA-FINE PARTICLES PREPARATION IN A DRY ROLLER VIBRATION MILL

The motion equations of the filling layers are established to study the motion traces of the filler in the chamber of vibration mill. The research results indicate that the filler does the rotary motion relative to the body center on the suitable vibration intensity, in the region of the center forms a steady circle motion, but in other regions forms a cascade motion, which makes up for the lack of the energy in the chamber's center and edge. Afterward, under a specific parameters combination, the single crystalline, transparent, uniform, randomly oriented, almost equiaxed Zn nanostructures are obtained in the roller vibration mill grinded 11 h, in order to test the simulation experiment.

SU-E-T-128: A Comprehensive Dosimetric Characterization of the New 160 Leaf Elekta Agility Collimator System

Purpose: A new MLC has been released that includes 160 leaves of 5mm width at isocenter that allows 40×40 cm2, rapid leaf speed, interdigitation, and reduced leaf transmission. We evaluate the dosimetric characteristics of this new Agility Collimator and its impacts on clinical applications. Methods: A dosimetric evaluation of the Agility and the MLCi2 collimator system is performed using a Wellhofer water tank, diode and ion chamber detectors, edge detectors, and rotational delivery QA tools. Characterization includes a comprehensive verification of beam quality (6, 10, and 15 MV), MLC transmission, and delivery efficiency and accuracy of IMRT and VMAT. Results: The Agility system has one set of diaphragm and the MLC replaces the entire X diaphragm, while the older MLCi2 has two sets of diaphragms. Examination of percent depth dose of the photon beam quality is identical except in the buildup region. MLCi2 has a slightly higher dose in the buildup region; attributed to more collimation material in the beam path. For Agility, the averaged MLC leakage is 0.003, and for MLCi2 the averaged leakage is 0.013. Agility (MLC along) is equivalent to MLCi2 (with backup diaphragm) to achieve low out‐of‐field radiation. With equivalent quality Philips Pinnacle3 IMRT and SmartArc/VMAT the delivery time is shorter on AGILITY because of higher MLC speeds and improvements in linac control software (Integrity R3.0) which supports continuously variable dose rate. Conclusion: This work demonstrates that the new Agility collimator assembly has similar beam quality as the original MLCi2 collimator system, except in the buildup region. Agility has less MLC leakage and increased delivery efficiency compared to MLCi2. These findings allow for an expedited commissioning of upgrade to the Agility from the MLCi2. Further features of the leaf speed are under investigation, including their potential for higher modulation in VMAT.

Thoughts on Simulating the VAPEX Process

Summary The vapour extraction (VAPEX) process and its many hybrid variants have attracted a great deal of attention as potentially lessenergy-intensive alternatives for exploiting heavy-oil and bitumen resources. However, despite significant work over the past 2 decades, uncertainty remains about the basic mechanisms, the scaling aspects, and the most appropriate methods of numerically simulating these processes. This paper offers some insights into several of these outstanding questions. The questions are examined in the context of an extensive and well-documented set of VAPEX experiments carried out by Maini and his colleagues over the past 10 years. We have experimented with different methods of simulating these experiments using a physics-based reservoir simulator. Despite the high permeability (greater than 200 darcies in all of the experiments), we find that capillary pressure plays a significant role in the drainage. The simulations suggest that most of the drainage takes place in the capillary transition zone along the edge of the vapour chamber, rather than in the single-phase zone ahead of it which has not yet been contacted by vapour. It has been emphasized in the literature that the near-linear scaling of oil rate with height observed in the experiments is dramatically different from the square-root-of-height dependence predicted by the original analytic model of VAPEX. However, the experiments also show an increasing solvent fraction in the produced-oil phase as height increases. When this "solvent mixing" effect is separated from the rates, the remaining height dependence is less than linear, though still greater than square root of height. The relative roles of molecular diffusion and mechanical dispersion in VAPEX have been discussed widely in the literature. Generally, mechanical dispersion is expected to play a larger role in these high-permeability experiments (compared with the field) because of larger fluid velocities. We present a method of inferring the diffusion/dispersion present in the simulations, despite a hidden component of numerical dispersion caused by the numerical method itself. We find that the experiments are well matched with values of diffusion and dispersion in line with literature correlations, and that the contribution of mechanical dispersion is perhaps not as large as might be expected relative to that of molecular diffusion. The paper also provides some thoughts on questions we expect are still unanswered, including mechanisms behind the height dependent mixing phenomenon and the scaling of the experimental results to the significantly greater heights and lower permeability characteristic of the field.

Modeling Steam-Assisted Gravity Drainage With a Black-Oil Proxy

Summary This paper describes an alternative approach to model steam-assisted gravity drainage (SAGD) with an isothermal black-oil (BO) reservoir simulator. The oil-viscosity reduction caused by heating in the actual SAGD process is emulated by a tuned saturated pseudo-oil viscosity relation in which solution gas/oil ratio (Rs) is used as a “proxy for temperature.” In the BO formulation, fully saturated oil viscosity (μo*) at reservoir pressure equals μo that would be attained at steam-chamber temperature (T*) in the actual SAGD process; initial oil viscosity (μoi) with initial Rs = 0 represents initial oil viscosity at reservoir temperature; and BO gas properties represent steam at T*. After careful analysis of the SAGD process, one finds that oil flows only along a narrow zone along the outer edge of the steam chamber—the “edge oil-flow zone.” The temperature gradient within this narrow zone is perpendicular to the oil-flow direction and is practically impossible to model with any precision because of the large temperature variation and dynamic steam-chamber shape over time. The BO-model solubility gradient also varies, analogous to temperature in a thermal model, from zero to fully saturated (Rs*) with an associated drop in oil viscosity from μoi to μo*. SAGD design requires many hundreds of runs to find operational conditions that maximize economic value (e.g., injector and producer location, rates, pattern spacing, and steam-chamber temperature T*). The proposed BO proxy model runs several times faster than a thermal model while maintaining similar performance behavior. The proxy-model saturated pseudo-oil viscosity μo(p) relation used is found by history matching a full-physics thermal-model performance prediction of oil rate, bottomhole flowing pressure, and cumulative oil for a 2D homogeneous model. We have found a single-constant μo(p) equation that yields a good match to thermal SAGD performance. The tuned pseudo-oil viscosity relation honors the measured initial reservoir and fully heated (at T*) oil viscosities. Its dependence on Rs is not physical, but reflects the use of Rs as a transform variable for temperature, capturing the strong spatial variation of temperature and oil viscosity within the localized steam/oil boundary region in which oil has been mobilized. The pseudo-oil viscosity relation, defined by a single empirical best-fit constant n—for a given T* and a set of thermal properties—appears to be applicable for a wide range of reservoir heterogeneity, injection and production rates, and well placement. Consequently, it should be possible to use the BO proxy model for SAGD optimization of T*, control rates, and injector/producer vertical-depth difference. We also see the potential of using the BO proxy model for solvent-based SAGD, with the pseudo-oil viscosity model depending on both T* and solvent; thermal compositional modeling is yet even slower and less suitable for optimization.

Impact of static magnetic fields on the radial line slot antenna plasma source

The radial line slot antenna plasma source is used in semiconductor device fabrication. As is the case for all plasma sources, ever more strict uniformity control requirements are driven by the precision demands of new device technologies. Large volume diffusion plasmas, of which the radial line slot antenna source is one type, must overcome transport effects or diffusion modes that tend to “center peak” the plasma density near the wafer being processed. One way to resolve problematic transport effects is the insertion of magnetic fields into the plasma region. In this paper, the impact of the magnetic field on plasma properties is parameterized as a function of slot configuration. The magnetic field orientation and the magnitude of magnetic field are varied in a computational study in which the source is modeled as a two-dimensional axisymmetric quasineutral plasma. This work employs a finite element model simulation. The magnitude of magnetic fields considered is 50 Gauss maximum with a microwave power of 3000 W at a pressure of 20 mTorr. 20 mTorr is chosen as this is a condition where diffusion effects are challenging to counteract. The study showed that there are specific conditions for slot configuration and magnetic field that improve the plasma controllability and some that do not. Plasma property modulation is most effective when the plasma source region is placed at large radius with axial magnetic fields. There are synergistic effects between the slot location and magnetic field that are important and placing large magnetic fields at the chamber edge alone does not result in improved uniformity. Electron cyclotron resonance (ECR) heating and the impact of pulsing the magnetic fields are presented. ECR heating is not important for the conditions relevant to this paper and pulsing is shown to have benefit.

A New Thermogeomechanical Theory for Gravity Drainage in Steam-Assisted Gravity Drainage

Summary Oil-sands reservoirs in western Canada hold more than 170 billion bbl of recoverable heavy oil and bitumen representing a significant source of unconventional oil. At in-situ conditions, the majority of this oil has essentially no initial mobility because of its high viscosity, which is typically in the hundreds of thousands to millions of centipoises. In steam-assisted gravity drainage (SAGD), steam injected into the formation heats oil at the edge of a depletion chamber, thus raising the mobility, ko/μo, of bitumen. Three main effects account for the increase of oil mobility. First, bitumen at steam temperature has viscosity typically less than 20 cp. Second, it is believed that shear, which is caused by thermal-expansion gradients, dilates the oil sand and causes enhanced permeability. Third, dilation at the chamber edge leads to smaller residual oil saturation (ROS). Because the production rate of SAGD is directly tied to the drainage rate of mobilized oil at the chamber edge, the thermogeomechanics of the oil sand at the chamber edge is a control on the performance of SAGD. In this study, a novel SAGD formula is derived that accounts for thermogeomechanical effects at the edge of the chamber. This paper couples dilation effects arising from thermal expansion into an analytical model for SAGD oil rate. The results reveal that volumetric expansion at the edge of the chamber plays a significant role in enabling effective drainage of bitumen to the production well.

Understanding the Heat-Transfer Mechanism in the Steam-Assisted Gravity-Drainage (SAGD) Process and Comparing the Conduction and Convection Flux in Bitumen Reservoirs

Summary SAGD is one successful thermal recovery technique applied in the Athabasca and Peace River reservoirs in central and northern Alberta, Canada. In SAGD, steam is injected into a horizontal injection well and is forced outward, losing its latent heat when it comes into contact with the cold bitumen at the edge of a depletion chamber. As a consequence, the viscosity of the bitumen falls several orders of magnitude, its mobility rises several orders of magnitude, and then it flows under gravity toward a horizontal production well located several meters below and parallel to the injection well. Heat-transfer mechanisms are pivotal to the SAGD process. Though heat energy is transferred from steam to reservoir by conduction and convection, heat transfer by convection is not considered in the classic SAGD mathematical models such as Butler?s. Researchers such as Butler and Stephens (1981), Reis (1992), Akin (2005), Liang (2005), Nukhaev et al. (2006), and Azad and Chalaturnyk (2010) considered conduction from steam to cold reservoir to be the only heat-transfer component. However, because the heat capacity of water is typically two to five times that of bitumen, convection caused by the mobile condensate flow in the reservoir may contradict these studies. Farouq-Ali (1997) was the first to criticize the assumption that there is only a thermal conduction mechanism in the SAGD process. He pointed out that with so much condensate flowing, convection would be expected to be the dominant heat-transfer mechanism, which can be plausible at high temperatures. In response, Edmunds (1999a) stated that on the basis of the associated change in enthalpy, the heat transfer into a cold reservoir because of convection is probably less than 5% of that because of conduction. Ito (1999) challenged Edmunds (1999a) statement, on the basis of Ito and Suzuki (1996, 1999) and Ito et al. (1998), pointing out that "this number, 5%; i.e., ratio between convection to conduction presented by Edmunds (1999a) is unrealistically low, (and) it should be in the range of 50%. This study examined the relative roles of convective and conductive heat transfer at the edge of SAGD steam chambers. In summary, the mathematical model developed in this study considered both conduction and convection, and the resultant output from the model is reasonably consistent with published field data. This study supports the idea that although convection can dominate near the chamber edge in high-water-saturation reservoirs, in bitumen-rich reservoirs, its contribution to heat transfer is less than 1% and can be neglected.

Understanding the Heat-Transfer Mechanism in the Steam-Assisted Gravity-Drainage (SAGD) Process and Comparing the Conduction and Convection Flux in Bitumen Reservoirs

Summary SAGD is one successful thermal recovery technique applied in the Athabasca and Peace River reservoirs in central and northern Alberta, Canada. In SAGD, steam is injected into a horizontal injection well and is forced outward, losing its latent heat when it comes into contact with the cold bitumen at the edge of a depletion chamber. As a consequence, the viscosity of the bitumen falls several orders of magnitude, its mobility rises several orders of magnitude, and then it flows under gravity toward a horizontal production well located several meters below and parallel to the injection well. Heat-transfer mechanisms are pivotal to the SAGD process. Though heat energy is transferred from steam to reservoir by conduction and convection, heat transfer by convection is not considered in the classic SAGD mathematical models such as Butler's. Researchers such as Butler and Stephens (1981), Reis (1992), Akin (2005), Liang (2005), Nukhaev et al. (2006), and Azad and Chalaturnyk (2010) considered conduction from steam to cold reservoir to be the only heat-transfer component. However, because the heat capacity of water is typically two to five times that of bitumen, convection caused by the mobile condensate flow in the reservoir may contradict these studies. Farouq-Ali (1997) was the first to criticize the assumption that there is only a thermal conduction mechanism in the SAGD process. He pointed out that with so much condensate flowing, convection would be expected to be the dominant heat-transfer mechanism, which can be plausible at high temperatures. In response, Edmunds (1999a) stated that on the basis of the associated change in enthalpy, the heat transfer into a cold reservoir because of convection is probably less than 5% of that because of conduction. Ito (1999) challenged Edmunds (1999a) statement, on the basis of Ito and Suzuki (1996, 1999) and Ito et al. (1998), pointing out that “this number, 5%; i.e., ratio between convection to conduction presented by Edmunds (1999a) is unrealistically low, (and) it should be in the range of 50%.” This study examined the relative roles of convective and conductive heat transfer at the edge of SAGD steam chambers. In summary, the mathematical model developed in this study considered both conduction and convection, and the resultant output from the model is reasonably consistent with published field data. This study supports the idea that although convection can dominate near the chamber edge in high-water-saturation reservoirs, in bitumen-rich reservoirs, its contribution to heat transfer is less than 1% and can be neglected.

Monitoring of SAGD Steam-Chamber Conformance by Using White-Noise-Reflection Processes

Summary Thermal stimulation of bitumen in oil-sands reservoirs is a critical requirement for the success of steam-based recovery processes such as steam-assisted gravity drainage (SAGD). If the bitumen is not heated, it remains at its original viscosity, often in the millions of centipoise and, thus, is not mobilized so that it cannot be moved to a production well. All oil-sands reservoirs are heterogeneous, both with respect to geology and fluid composition, and, thus, conformance of steam in the reservoir is not uniform. At present, real-time monitoring of the steam-conformance zone in the reservoir is not possible, and, thus, the spatial distribution of heat delivery to the reservoir is uncertain. In this research, a new method for detecting heterogeneity and monitoring steam chambers has been developed and tested by detailed thermal/acoustic reservoir simulation. Here, a thermal fluid-flow simulator was one-way coupled to a wave-propagation simulator (information passed is density alone) to evaluate the potential of identifying rock and fluid discontinuities during a SAGD operation with coded white-noise-reflection processes. Digital communication systems use coded white-noise processes to make advantageous use of unexpected reflections from environmental heterogeneities. The proposed theory and subsequent simulations reveal that it is possible to resolve the edge of the SAGD steam chamber and to image the heterogeneity within the reservoir as it evolves with white-noise-reflection methods. The properties of the signals described provide an opportunity for property detection at lower power levels and higher frequencies than traditional seismic methods. Furthermore, the signals are such that the noise from recovery processes and the native reservoir environment do not interfere with the detection methods, allowing for the monitoring method to be used concurrently with the recovery process.

Influence of atomic processes on the implosion of plasma liners

The influence of atomic physics processes on the implosion of plasma liners for magneto-inertial nuclear fusion has been investigated numerically by using the method of front tracking in spherically symmetric geometry and equation of state models accounting for dissociation and ionization. Simulation studies of the self-collapse of argon liners to be used in the Los Alamos Plasma Liner Experiment (PLX) program have been performed as well as studies of implosion of deuterium and argon liners on plasma targets. Results show that atomic processes in converging liners reduce the temperature of liners and increase the Mach number that results in the increase of the stagnation pressure and the fusion energy gain. For deuterium and argon liners imploding on plasma targets, dissociation and ionization increased the stagnation pressure and the fusion energy gain by the factor of 1.5 (deuterium) and 2 (argon) correspondingly. Similarly, ionization during the self-collapse of argon liners leads to approximately doubling of the Mach number and the stagnation pressure. The influence of the longitudinal density spread of the liner has also been investigated. The self-collapse stagnation pressure decreased by the factor of 8.7 when the initial position of the liner was shifted from the merging radius (33 cm) to the PLX chamber edge (137.2 cm). Simulations with and without the heat conduction demonstrated that the heat conduction has negligible effect on the self-collapse pressure of argon liners.

Learning Equipment for the Flammability Limits of Liquefied Petroleum Gas

Problem statement: This article was developing learning equipment for flammability limit behavior which designed for study the relation of Liquefied Petroleum Gas (LPG) and combustion. The equipment can be use as an instructional media for obviously experiment of combustion. Approach: The test chamber was designed by using the stainless as a structure. The mirror with safety film was used for safety purpose to the tester. The mirror was the additional equipment for the ignition vision. The size of test chamber was 40×25×20 cm. The top of chamber can be opened when the ignition was occurred to reduce the inner pressure that can break the mirror or can be a cause of damage to other parts. The 2 of stainless plates with the size of 15×40 cm. were used and the hinges were attached at the upper edges of the chamber from both sides. The metal was closely attached at the chamber edge to reduce the leak of fuel to outer environment. The bottom structure of the chamber installs the control mainboard of electronics system and motor. The control of heat gain system inside the heat chamber. Results: The test chamber is designed to demonstrate the ignition. So, the size has to be suitably designed and large enough for convenience in monitoring. It can be seen that when the test is conducted in a real system, the result is extremely differed from the theory. The reason is the experimentation by the theory using the cup burner or a cylindrical glass cup. This cup has an outside diameter of 28 mm. and around the cup tunnel has an inside diameter of 8.5 or 9.5 cm with 53.5 cm. of height. The ratios of both testing equipments are extremely differed, so there is an opportunity that the accuracy is highly shifted. Conclusion: The test chamber shows that the flammability limit of LPG vary with temperature and can be compare with burgess-wheeler law. This law mentioned “LFL and UFL is relative with the chemical in Paraffin Hydrocarbon (Alkane) Group in any increasing of temperature” In addition, there are many flammability and backfire theory which interesting for experiment.

Automated Screening of Fetal Heart Chambers from 2-D Ultrasound Cine-Loop Sequences

Fetal cardiac ultrasonic imaging technique has become increasingly popular in the recent years for the detection of fetal congenital abnormalities at an early stage. Due to the low signal-to-noise ratio of the ultrasound imaging, the automatic detection methods should incorporate suitable preprocessing filtering techniques to enhance the segmentation techniques efficiently. This paper suggests the application of median and morphological filtering operation for removing speckle noise. Then the four heart chambers are segmented independently based on the shape priors. The amorphous snake’s helps in identifying the contours of the chamber edges individually based on shape pattern. Experimental study involves the ultrasound cine-loop sequences of the apical four chamber view of fetal heart with a constant frame rate of 25 frames per second (fps) with varying duration of 10-30s encompassing a range of 20-40 complete cardiac cycles. The simulation result confirms the suitability of proposed scheme for automated screening of fetal heart chambers.

New thermal-reactive reservoir engineering model predicts hydrogen sulfide generation in Steam Assisted Gravity Drainage

In Steam-Assisted Gravity Drainage (SAGD), high pressure, high temperature steam is injected into a bitumen-bearing oil sands formation. For most operations, the steam temperature ranges from about 200 to 260°C and thus under these conditions, the bitumen undergoes hydrous pyrolysis, i.e. aquathermolysis, yielding acid gases such as hydrogen sulfide and carbon dioxide. Current SAGD thermal reservoir simulation models often take into account complex spatial heterogeneity of the geology and oil composition and the physics of heat transfer, multiphase flow, gas solubility effects, and viscosity variations with temperature, however, none so far in the literature take the detailed chemistry and reaction engineering of bitumen aquathermolysis during field scale SAGD into account. Here, we have added aquathermolysis reactions to a thermal reservoir simulation model to understand the reactive zones in the SAGD process and how the process generates acid gases via aquathermolysis. The results reveal that chemical reactions have a significant effect on the growth of the SAGD steam chamber and that the majority of the reactive zone is in the liquid pool that sits above the production well. The product gases of aquathermolysis reduce the efficiency of steam heat delivery capacity to the chamber edge. The results demonstrate that this effect can be reduced by lowering the steam injection pressure. This new model is capable of predicting acid gases like hydrogen sulfide, carbon oxides and fuel gases like hydrogen, methane as observed during SAGD field operations.

The Nest Architecture of Three Species of North FloridaAphaenogasterAnts

The architecture of the subterranean nests of Aphaenogaster floridana Smith (Hymenoptera: Formicidae), A. treatae Forel and A. ashmeadi (Emery), was studied from plaster, wax, or metal casts. After structural features were quantified from digital images, the entombed ants were retrieved from the plaster by dissolution or wax casts by melting and counted. Nests of all three species were rather simple, small and vertical, with horizontal chambers connected by vertical shafts. Shafts descending to lower chambers tended to arise from chamber edges, whereas those connecting to a chamber above tended to arise from chamber centers. A. floridana had the largest nests and colonies, and multiple shafts commonly connected upper chambers, a feature lacking in the other two species. In A. floridana nests a higher proportion of chamber area and greater spacing between chambers occurred in the deeper parts of the nest, regardless of nest size. The other two species showed no vertical differentiation of any size-free measure at any nest size. In all three species, nest size increased more slowly than the worker population, so crowding was greater in large colonies than in small, in contrast to the situation in three other ant species for which data were available. An appendix with stereo images of all casts is provided.

Ant-nest ichnofossils in honeycomb calcretes, Neogene Ogallala Formation, High Plains region of western Kansas, U.S.A.

Two new ant-nest trace fossils are described from calcic sandy paleosols of the Neogene Ogallala Formation in western Kansas. The ichnofossils are preserved within and below calcrete beds weathering in positive relief as carbonate-filled casts or as cavities in negative relief. Daimoniobarax ichnogenus nov. is established for burrow systems composed of vertically tiered, horizontally oriented pancake-shaped chambers connected by predominantly vertical and cylindrical shafts ~ 0.8 cm in diameter. Ichnospecies of Daimoniobarax are differentiated based on differences in the plan view outline of chambers, shaft orientation, and junctions between chambers and shafts. Daimoniobarax nephroides ichnospecies nov. is composed of an ~ 24–76 cm long vertical sequence of distinctly lobed chambers (~ 2–20 cm wide and ~ 1 cm high) arranged along sinuous to helical shafts. Chamber shape in plan view ranges from small teardrops to larger kidney- and U-shaped forms. Shafts intersect at chamber edges such that chambers appear to bud from the central shafts. Daimoniobarax nephroides is most similar to the nests of extant seed-harvester ants of the New World genus Pogonomyrmex. Such ants are specialized granivores and prefer sandy soils in arid to semi-arid grassland and desert regions. Daimoniobarax tschinkeli ichnospecies nov. is ~ 30–80 cm in vertical extent. Chambers (~ 2–30 cm wide and ~ 1 cm high) are circular to elongate or pseudopodial in plan view. Vertical shafts are straight to slightly sinuous and intersect most often toward the center of the chambers. The generalized architecture of D. tschinkeli is similar to that of the nests or nest portions of several extant ant genera, though it does not closely resemble any known modern nest. Ant ichnofossils provide valuable information on hidden biodiversity, paleohydrologic regimes, paleopedogenic processes, and paleoclimate during the time of nest occupation. Depth-related changes in chamber size and vertical spacing may also help interpret paleosurfaces and paleodepths, and serve as geopetal features.

Main chamber sources and edge transport of tungsten in H-mode plasmas at ASDEX Upgrade

In the fully tungsten clad ASDEX Upgrade, the sputtering rates of tungsten have been determined at all relevant plasma facing components using fast spectroscopic measurements with temporal resolution down to 0.5 ms. The sputtering strongly increases during an edge-localized mode (ELM) and the ELMs are often the dominant cause of tungsten sputtering. A modelling approach was employed to calculate the tungsten source at the limiters and the resulting tungsten density at the pedestal top inside the H-mode edge transport barrier (ETB). In the ETB, it is assumed that tungsten transport is collisional, i.e. behaves like other impurities. The collisional transport leads to strong inward drifts and steep density gradients in the ETB, which are flattened during an ELM causing an efflux of tungsten. The collisional transport in the ETB is also calculated for typical ITER conditions and the resulting tungsten density profiles as well as the transport of the helium ash through the ETB are evaluated.

Convection at the Edge of a Steam-Assisted-Gravity-Drainage Steam Chamber

Summary Steam-assisted gravity drainage (SAGD) has become the preferred process to recover bitumen from Athabasca deposits in Alberta. The method consists of a lower horizontal production well, typically located approximately 2 m above the base of the oil zone, and an upper horizontal injection well located roughly 5 to 10 m above the production well. Steam flows from the injection well into a steam chamber that surrounds the wells and releases its latent heat to the cool oil sands at the edge of the chamber. This research re-examines heat transfer at the edge of the steam chamber. Specifically, a new theory is derived to account for convection of warm condensate into the oil sand at the edge of the chamber. The results show that, if the injection pressure is higher than the initial reservoir pressure, convective heat transfer can be larger than conductive heat transfer into the oil sand at the edge of the chamber. However, enhancement of the heat-transfer rate by convection may not necessarily imply higher oil rates; this can be explained by relative permeability effects at the chamber edge. As the condensate invades the oil sand, the oil saturation drops and, consequently, the oil relative permeability falls. This, in turn, results in the reduction of the oil mobility, despite the lowered oil viscosity because of higher temperature arising from convective heat transfer.

Stability of the edge of a SAGD steam chamber in a bitumen reservoir

Steam-Assisted Gravity Drainage (SAGD) is a key in-situ recovery process being used today to extract oil from bitumen reservoirs. In SAGD, an oil-depleted chamber of steam grows within the oil sands formation along a pair of horizontal wells and heats bitumen-laden oil sands at its edge. The viscosity of bitumen drops by up to five orders of magnitude when heated to above 200 °C and mobilized bitumen at the chamber edge flows under gravity to a production well located at the base of the chamber. If the steam chamber does not grow uniformly along the wellpair, then bitumen recovery is less than ideal. To raise the thermal efficiency, and consequently the economics, of the process, efficient heat transfer from chamber to the oil sands must occur and the chamber must grow uniformly along the entire length of the wellpair. If steam fingers develop at the edge of the chamber, then the heat transfer area enlarges and raises the thermal efficiency of the process since more heat is directed to the oil sands. In this research, the stability of the interface between the steam chamber and oil sands is examined by using linear stability theory. The results show that the stability is controlled by the difference between the energy content-weighted Darcy–Rayleigh numbers of the steam/water phases (displacing fluid) and the oil phase (displaced fluid). Also, the results show that at typical SAGD steam saturation temperatures, the chamber edge is unstable providing the steam quality at the edge exceeds about 50%.

Anterior Chamber Depth Measurement in Pseudophakic Eyes: A Comparison of Pentacam and Ultrasound

To compare the anterior chamber depth (ACD) measurements of a Scheimpflug camera (Pentacam, Oculus Optikgeräte GmbH) and immersion ultrasound biometry (UltraScan Imaging System, Alcon Laboratories) in pseudophakic eyes. This prospective, multicenter study included three independent sample groups. The ACD, defined as the distance between the corneal epithelium and intraocular lens anterior surface, was assessed by ultrasound biometry. Two Pentacam ACD measurements were evaluated--the value automatically provided by the internal software and a manual measurement obtained by moving the software calipers on a single Scheimpflug image. For the comparison group (12 eyes), no significant difference between the mean ultrasound biometry and mean Pentacam manual measurement (4.51+/-0.34 mm and 4.50+/-0.34 mm, respectively, P>.05) was noted, whereas the mean automatic value was significantly higher (4.94+/-0.41 mm, P=.0002), as the posterior edge of the anterior chamber is erroneously identified as coinciding with the boundary of the posterior capsule. A strong correlation was found between Pentacam manual measurements and ultrasound biometry (r=0.98, P<.0001); this correlation was confirmed by the confirmation group (17 eyes), whose mean values were 4.76+/-0.39 mm and 4.72+/-0.37 mm, respectively (r=0.98, P<.0001). After merging the data for the comparison and confirmation groups, the difference between Pentacam manual measurements (4.65+/-0.38 mm) and ultrasound readings (4.63+/-0.38 mm) was not statistically significant. For the assessment group (15 eyes), relative repeatability and reproducibility of Pentacam manual measurements were 1.17% and 1.59%, respectively. In pseudophakic eyes, the Pentacam provides ACD values that do not statistically differ from those of ultrasound immersion biometry, on the condition that manual measurements are used rather than automatic ones.