Abstract The performance of air sparging systems, as measured by the predicted region of airflow, was investigated by conducting numerical simulations with a multiphase modeling program (TETRAD). The simulations employed standard two‐phase flow theory, and included pressure‐dependent calculations of the compressibility of water and air. Simulations tested the response of air sparging systems to variations in geological properties (intrinsic permeability and anisotropy of permeability) as well as different injection scenarios (depth, pressure, and rate of injection). Three stages of flow behavior are predicted following initiation of air injection. These are: (1) an initial transient period of growth in the lateral and vertical limits of airflow (expansion stage); (2) a second transient period of reduction in the lateral limits of airflow (collapse stage); and (3) a steady‐state stage, during which the system remains static as long as injection parameters do not change. In homogeneous media the geometry of the region of airflow changes from a teardrop‐or bell‐shaped configuration to a shape that is roughly conical during the expansion stage. During the collapse stage, air is preferentially diverted to established regions of high effective air permeability, and ground water resaturates the remainder of the original region of influence. For pilot testing it is important to realize that measurements of the lateral extent of airflow expansion and collapse stages can be misleading because they will differ from the limits established at steady‐state. The time required for a particular system to progress through the transient stages and establish steady‐state behavior can vary from hours to years, and is dependent on the permeability structure of the aquifer, injection depth, and injection rate. Under homogeneous conditions the maximum width of the region of airflow attained during the transient expansion stage was substantially greater than the width attained at steady‐state. The width of the steady‐state region of airflow is significantly affected by all the variables investigated, except injection depth, which appears to primarily influence the transient behavior. The simulations further show that the vertical permeability and anisotropy of the aquifer are very important variables, and warrant routine assessment during design of sparge systems. Simulation of heterogeneous media demonstrate that complex airflow patterns will occur as a result of air ponding beneath, and flow around, zones of low air permeability.
Abstract This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies.
The flow behavior of an air sparging pilot test was simulated using a finite difference, multiphase flow simulator (TETRAD). The field test is one of the only examples where the airflow pattern in the saturated zone is well known. This is a result of the relative homogeneity of the aquifer and the use of an advanced geophysical monitoring technique known as electrical resistance tomography (ERT). ERT is sensitive to the changing water content of the saturated zone during the test and provided a clear image of the size and shape of the principal region of airflow. In addition to ERT results, slug tests and core analyses provided other key calibration data. The multiphase flow simulations provided a good match to the observed pattern of airflow and pressure changes, indicating that such simulations may be useful for evaluating air sparging performance under other conditions.
This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies.
