Rajiv Srivastava

Atomistic Simulation of Conduction and Diffusion Processes in Nafion Polymer Electrolyte and Experimental Validation

Conduction and diffusion processes in Nafion 117 polymer electrolyte were analyzed using all-atom molecular dynamics models. The diffusivity of methanol, water, hydronium, and proton in Nafion and the conductivity of Nafion were evaluated in a wide range of temperatures from 20 to 120°C for various water contents (λ = 3.0, 13.0, and 22.0). To validate the simulation results, the conductivity of Nafion was evaluated using a four-probe conductivity measurement apparatus at temperatures from 20 to 120°C in humidified air (RH=50 to 100%) and in liquid water. The permeability of methanol in Nafion was evaluated using a high-temperature membrane diffusion cell. The calculated values and experimental results are generally in good agreement with maximum differences within 50% at room temperature or 100% at higher temperatures.

Electrical resistance tomography for real-time mapping of the solid-liquid interface in tanks containing optically opaque fluids

The visualization of settled solid layers in vessels have many applications, of interest here is for facilitating the efficient retrieval of high-level radioactive waste (HLW) from underground storage tanks at Department of Energy sites. Visualization of the solids interface with opaque liquid above can’t be accomplished by regular optical imaging methods and hence our interest in using Electrical Resistance Tomography (ERT). The ideal arrangement for 3-D ERT imaging inside tanks is to use a multiple ring electrode system, which is complex and expensive. This research describes ERT imaging done with a single linear array as a benchmark study to ascertain the viability of its imaging of the interface. Experiments focused upon systematic analysis of many ERT tomograms of two simple settled solids layers (horizontal, 30o) using pulverized kaolin clay (10μdia) and water. Visualization was done using commercial ERT software. Injection current and electrode orientation were the two system parameters varied and analyzed. Reproducibility, accuracy and reliability of this ERT system will be presented.

Monitoring the solid-liquid interface in tanks using profiling sonar and 3D visualization techniques

Visualization of the interface between settled solids and the optically opaque liquid above is necessary to facilitate efficient retrieval of the high-level radioactive waste (HLW) from underground storage tanks. A profiling sonar was used to generate 2-D slices across the settled solids at the bottom of the tank. By incrementally rotating the sonar about its centerline, slices of the solid-liquid interface can be imaged and a 3-D image of the settled solids interface generated. To demonstrate the efficacy of the sonar in real-time solid-liquid interface monitoring systems inside HLW tanks, two sets of experiments were performed. First, various solid objects and kaolin clay (10 μm dia) were successfully imaged while agitating with 30% solids (by weight) entrained in the liquid. Second, a solid with a density similar to that of the immersed fluid density was successfully imaged. Two dimensional (2-D) sonar images and the accuracy and limitations of the in-tank imaging will be presented for these two experiments. In addition, a brief review of how to utilize a 2-D sonar image to generate a 3-D surface of the settled layer within a tank will be discussed.