Air Saturations Research Articles

Multi-phase flow modeling of air sparging

Air injection into groundwater (air sparging) in a homogeneous axially symmetric porous medium is modeled using a two-phase flow approach. A numerical method based on the mixed form of the Richards equation for both phases is presented. Furthermore two analytical approximations are discussed to explain the numerical results. One is a one-dimensional description explaining the occurrence of small air saturations. The other is a closed form approximation for the distribution of the air saturation in the resulting steady state. From the latter we can estimate the maximum radius of influence of air sparging, as a function of the physical parameters. The analytical approximation at steady state and the numerical results are in good agreement.

Velocity and Graviresponses in Paramecium during Adaptation and Varied Oxygen Concentrations

Summary Populations of Paramecium caudatum adapted to new O 2- and chemical environments within at least 6 hours show two subgroups of cells which are distinguished by their median swimming velocity. “Fast swimmers” prevailed at the beginning, and “normal swimmers” toward the end of the adaptation period. The median swimming rate of these two groups was largely constant throughout 6 hours, apart from initial disturbances following transfer into a closed environment. The degree of air saturation of the experimental solution (5% to 100%) was monitored continuously in a new flow-through chamber. Changes in the O 2 level did not have a consistent effect on the swimming velocity. Negative gravitactic orientation in normal swimmers gradually decreased with incubation time. Gravitaxis was absent in the fast swimmers. Variation in O 2 tension did not produce perceptible effects on gravitaxis. At all air saturations and incubation times negative gravikinesis was found, both in normal and in fast swimmers, centering near −40 µm/s. Gravikinesis correlated with swimming velocity, but not with O 2 tension. No correlation was found between the kinesis and orientation coefficients. The data suggest that gravikinesis in Paramecium is largely independent of O 2 levels and adaptation time. Graviorientation declines with adaptation, but is not a direct function of O 2 saturation of the medium.

Secondary Water Recovery by Air Injection: 3. Evaluation of Feasibility

Numerical simulation indicated that secondary water recovery by air injection could be technically feasible in aquifers with thick unsaturated zones, confining top layers, high ratio of horizontal‐to‐vertical permeability, and low intrinsic permeability, and high irreducible air saturations, i.e., clayey textures. Injection at the top of the unsaturated zone, venting the well to the atmosphere immediately after the end of air injection, low‐to‐moderate injection rates and large volumes of injected air seemed to enhance water recovery. Simulated water recovery volumes were significantly lower than the recovery estimates based on water level elevations in observation wells during field tests. The model helped interpret some of the observations made during the field tests of secondary water recovery and helped identify areas of inadequacy in available information needed for representative numerical simulations.

Bubble Formation and Modification in the Sea and its Meteorological Significance

It is believed that the vast majority of the airborne salt nuclei arise from bursting bubbles at the air—sea water interface. Four natural mechanisms for the production of these bubbles have been studied. These are whitecaps, rain, snow and supersaturation of the surface waters of the sea due to spring warming. The bubble spectra from whitecaps and snowflakes have been measured and semi-quantitative and qualitative observations have been made on the bubble spectrum produced by raindrops. No evidence of bubble production by spring warming has been obtained.
 All of the measurements show that a majority of the bubbles are < 200 microns diameter and, in the case of bubbles from snowflakes, < 50 microns. In the vicinity of a breaking wave the bubble production rate is about 30 cm−2 sec−1.
 Due to the effects of surface tension in increasing the bubble internal pressure all bubbles < 300 microns will go into solution even at sea water air saturations of 102 percent. Bubbles < 20 microns will go into solution at saturations up to 115 percent! The solution time for small bubbles of about 10 microns is about 10 sec and is not markedly affected by the water saturation percentage.
 It is concluded that the effects of the rate of solution of bubbles in sea water can, under some conditions, play a significant role in modifying the initial bubble spectrum. This, in turn, should influence the spectrum of airborne nuclei.