Lorentz forces provide a unique method for the control and mixing of gas flows without the physical intrusion of objects into the flow. Lorentz forces arise when an electric current is passed through a volume in the presence of a magnetic field. The interaction between the electric current and the electric and magnetic fields produces a body force which affects the flow. These forces have been investigated experimentally by other researchers and show promise as a way to accelerate combustion in diffusion flames by increasing the mixing rate of fuel and oxidant streams. Theoretical and numerical models were developed to gain insight into this process. Alkali metal seeding raises the electrical conductivity of a flame by two to three orders of magnitude. This has two significant effects: the Lorentz force becomes stronger for the same applied electric current and magnetic field, and the alkali seed concentration becomes a dominant factor in determining electrical conductivity of seeded gases. This makes electrical conductivity much easier to predict, and so the Lorentz body force produced is easier to determine. A theoretical basis for numerical modeling of reactive flows with variable body forces has been developed. Many issues are important in simulating gas flows. Conservation of chemical species must be carefully maintained. Mass transport by gaseous diffusion, which limits combustion rates in a diffusion flame, must be appropriately modeled. Viscous action is also important, since it promotes mixing of the fuel and oxidant streams. Convective, conductive, and diffusive transport of energy must be carefully treated since energy transport directly affects the fluid flow. A numerical model of an incompressible gas flow affected by Lorentz forces was written and tested. Although assumptions made in the model, such as isothermal conditions and uniform density, are not found in diffusion flames, the numerical model predicts velocity vector patterns similar to those observed in actual Lorentz force tests on diffusion flames. A simulation code for compressible, reactive gas flows which include Lorentz forces has also been written. Several parts of the model have been validated, and the approach used appears likely to produce successful simulations. Further validation studies will be required, however, before complete modeling of the diffusion flame can proceed. / Graduation date: 1995

A gas-diffusion tracer experiment was conducted at the ChemNuclear, Inc., nuclear waste burial site near Barnwell, South Carolina, on June 1-10; 1981, testing a new methodology to measure the in situ gaseous diffusion characteristics of unsaturated porous media for the purpose of estimating the diffusive flux of volatile contaminants from the burial ground. The tracers used were CClBrF₂ and SF₆. They were released in the subsurface from permeation devices that closely approximate an ideal point-diffusion source. The permeation devices contain the tracer in liquid form and allow the tracer to escape at a constant rate by diffusion through a Teflon membrane. The release rates for CClBrF₂ and SF6 during the test were 105 and 3.3 nanograms/second, respectively. These compounds were selected on the basis of their compatabi1ity with the permeation-release device, their absence in the subsurface, and detectability in the part-per-tri11ion range in soil gas. Analyses were made in the field on a Varian 3700 series gas chromatograph equipped with an electron-capture detector. The instrument was modified to introduce soil gas through sampling valves and a Nafion tube desiccant. The diffusion sources were placed in the unsaturated soil at depths of 2 meters and 13 meters below land surface. Diffusive movements of tracer were monitored for a period of 7 days and tracer breakthrough was observed at points up to 3.5 meters away. Diffusion was modeled using a three-dimensional, continuous point source, transient-state, analytical model which allowed estimation of the effective diffusion coefficient of the porous media, and an independent assessment of the media's sorptive effects on the tracer gas. The model was calibrated using least squares and curve matching techniques, the latter of which enables a field technician to quickly interpret observed field data. Field values obtained for effective diffusion coefficient ranged from 0.026 to 0.037 cm²/sec. The average tortuosity factor observed for test site was 0.705.

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