Faculty and Staff
Dr. Martha Mitchell
Professor and Department Head
Education | Experience | Publications | Presentations | Collaborators | Advisees | Courses Taught | Research
Dr. Martha Mitchell's Research
Dr. Mitchell’s research focuses on molecular-scale modeling and simulation to eludidate phenomena occurring in industrially-relevant processes. She has collaborators at Sandia National Laboratories and NASA/White Sands Test Facility. She currently has two M.S. students, Bhargav Indurthi and Choudary Vellacheruvu working on research projects.
Research work is completed in the Computation and Visualization Laboratory in Jett Hall. The cluster contains one SGI Octane and three high-end PCs. The addition of the Sun cluster to the departmental resources through an Academic Equipment Grant has provided another platform for the CPU-intensive calculations that the simulations in this research require.
Computer-Aided Design of Fuel/Oxidizer Operations
In collaboration with NASA/JSC White Sands Test Facility, we are developing integrated computer codes for engineering design and safety analysis of all fuel oxidizer storage, distribution and on-orbit transfer operations under the full range of operating conditions, current and future. In work completed thus far, we used thermodynamic analysis to assess the hazards of the fuel Aerozine 50 under conditions of compression heating.
To assess the hazards of compression heating for fuels such as Aerozine 50, it was important to undertake an appropriate thermodynamic analysis of the behavior of the fuel under compression heating conditions. This analysis required determination of an appropriate equation of state, valid vapor pressure data and, for mixtures, appropriate thermodynamic mixing rules. In this project we propose to study the fuel Aerozine 50, a 50/50 mixture of hydrazine and unsymmetric dimethyl hydrazine.
Separation of light gas mixtures using inorganic molecular sieve membranes
Separating light gases using membranes is a technology area for which there exist opportunities for significant energy savings. Molecular sieve films offer the possibility of performing separations involving hydrogen, natural gas constituents and water vapor at elevated temperatures with very high separation factors. It is in applications such as these that we expect inorganic molecular sieve membranes to compete most effectively with current gas separation technologies. A membrane capable of separating H2 from other gases at high temperatures could recover hydrogen from refinery waste streams, facilitate catalytic dehydrogenation and promote the water gas shift (CO + H2O ® H2 + CO2) reaction. Natural gas purification requires separating CH4 from mixtures with CO2, H2S, H2O, CH4 and higher alkanes.
There is an on-going effort at Sandia by Dr. Tina Nenoff and co-workers that is funded through DOE/OIT and Chemical Industries of the Future: Vision 2020. Their goal is to computationally design and then synthesize inorganic molecular sieve membranes that (1) offer permeability, selectivity and enhanced thermal stability exceeding those of polymer membranes, and (2) are designed as specific gas membranes to compete with cryogenic and adsorption technologies for large-scale gas separation applications.
Our research provides an important complement to the synthetic effort at Sandia. Molecular dynamics simulations, which probe microscopic length scale events, provide diffusion information for binary mixtures. However, we have also found that longer length scale events are important contributors to the diffusion mechanism in molecular sieve films. To model these mesoscopic events we use transition-state theory. At this stage of the research our goal is to model the separation of binary mixtures of light gases in a variety of microporous systems: Zeolites A, ZSM-5, ZSM-11, novel zinc phosphates and titanosilicates The predictions from the simulations will then be incorporated into the synthetic effort, with the goal of both designing and synthesizing the exact system with maximum separation efficiency.
Molecular Density Functional Theory
In collaboration with Dr. Laura Frink at Sandia National Laboratories, we are embarking on a project to model ion movement in cell ion channels. The name of the code she has developed is called TRAMONTO. Our contribution will be to add electrostatic interactions to the code, and then to model ion channels of various diameters. The fundamental understanding that will be obtained from this modeling effort will be very important to experimentalists studying the action of ion channels.
Simulation of leaching of radioactive isotopes
In this project we are using microscopic and mesoscopic models to help elucidate mechanisms of the leaching of radioactive isotopes from zeolitic immobilization matrices. In recent years, interest has increased in molecular-scale modeling of industrial and environmental processes. Molecular dynamics simulations are used to calculate diffusion coefficients of water and the radioactive ions and molecule trajectories are monitored to observe mobility as a function of hydration level, temperature, and the flexibility of the zeolite lattice. On the time scale attainable in molecular dynamics simulations, the “rare event” phenomenon of ion migration will not be often seen. Thus the molecular dynamics simulations will be complemented with mesoscopic time scale transition state theory studies of ion and water diffusion. Although experimental studies have determined that zeolites are good candidates for immobilization of radioactive waste species, there is little molecular-level understanding of the mechanisms that contribute to this immobilization phenomenon. If zeolites are to be used as long-term storage media, a clear understanding of the mechanisms and factors influencing leaching must be obtained.