Month: March 2021

Title: Investigation into Pyrolysis and Gasification of Solid Waste Components and Their Mixtures

Author: Kiran Raj Goud Burra

Date/Time: March 29^th, 2021 | 11:00 AM

Dissertation Committee:
Professor Ashwani K. Gupta, Chair
Professor Nam Sun Wang
Professor Bao Yang
Professor Gary A. Pertmer
Professor Dongxia Liu, Dean’s Representative

Abstract:
Carbon neutral sources such as abundant biomass reserves and landfill-destined high energy density wastes such as plastics, and tire-wastes can be utilized together for energy and material production for a sustainable future. Pyrolysis and gasification can convert these variable feedstocks into valuable and uniform synthetic gas (syngas) with versatile downstream applicability to energy, liquid fuels, and other value-added chemicals production. But seasonal availability, high moisture and ash content, and relatively low energy density of biomass can result in significant energy and economic losses during gasification. Furthermore, gasification of plastic wastes separately was found to result in feeding issues due to melt-phase, coking, and agglomerative behavior leading to operational issues. To resolve these issues, co-processing of biomass with these plastics and rubber wastes was found to be promising in addition to providing synergistic interaction leading to enhanced syngas yield and inhibitive behavior in some cases and thus motivating this work. This dissertation provides a deconvoluted understanding and quantification of the source and impact of these interactions for better process performance and alleviation of inhibitive interaction needed to develop reliable co-gasification of feedstock mixtures. They address the knowledge gap in versatile feedstock-flexible gasifier development for efficient and reliable syngas production from varying solid waste and biomass component mixtures with minimal changes to the operating conditions.

TItle: Atomistic and theoretical description of liquid flows in polyelectrolyte-brush-grafted nanochannels

Author: Harnoor Singh Sachar

Date/Time: March 30, 2021 (Tuesday), 3:00 PM – 5:00 PM EDT

Zoom Link: https://umd.zoom.us/j/9765159282

List of Committee Members
Dr. Siddhartha Das (Chair)
Dr. Amir Riaz
Dr. Peter W. Chung
Dr. Don DeVoe
Dr. Silvina Matysiak (Dean’s Representative)

Abstract
Polyelectrolyte (PE) chains grafted in close proximity stretch out to form a “brush”-like configuration. Such PE brushes can represent a special class of nanomaterials that are capable of exhibiting stimuli-responsive behavior. They can be manipulated as needed by changing the environmental conditions like pH, solvent quality, salt concentration, temperature, etc. This responsiveness renders them very useful for a plethora of applications such as lubrication, emulsion stabilization, current rectification, nanofluidic energy conversion, drug delivery, oil recovery, etc. Therefore, gaining fundamental insights into PE brush systems is of utmost importance for both industrial as well as academic research. In this dissertation, we make use of theoretical and computational tools to improve our understanding of planar PE brushes and then use this understanding to probe flows in PE brush-grafted nanochannels.

We begin our quest by conducting all-atom Molecular Dynamics (MD) simulations to probe the microstructure of planar PE brushes with an unprecedented atomistic resolution. This allows us to not only investigate the properties of the PE chains but also the local structure and arrangement of the counterions and water molecules trapped within the brushes. Next, we use our atomistic model to probe the effects of variation in charge density on the microstructure of weak polyionic brushes. Such a variation in the charge density is typically enforced by a change in the surrounding pH and is a characteristic behavior of pH-responsive (annealed) PE brushes.

Furthermore, we go on to develop the most exhaustive theoretical model for pH-responsive PE brushes known as the augmented Strong Stretching Theory (SST). Our model is an improvement over the existing state-of-the-art as it considers the effects of the excluded volume interactions and an expanded form of the mass action law. We further improve this model by including several non-Poisson Boltzmann effects, especially relevant at high salt concentrations. This improved model is in excellent agreement with the results of our all-atom MD simulations.

Next, we use our augmented SST to model pressure-driven transport in backbone-charged PE brush-grafted nanochannels. Our results are an improvement over previous electrokinetic studies that did not consider a thermodynamically self-consistent description of the brushes. Finally, we conduct all-atom MD simulations to probe the pressure-driven transport of water in PE brush-grafted nanochannels using an all-atom framework. The nanoscale energy conversion characteristics obtained from our simulations are in reasonable agreement with the predictions of our continuum framework and lie within the range of values reported by a prior experimental study.

Title: Numerical and Experimental Studies on Dynamic Interactions of Robot Appendages with Granular Media

Date/Time: Mar 25, 2021, 12:15 PM EST

Committee Members:
Professor Balakumar Balachandran, Chair and Advisor
Professor Abhijit Dasgupta, Department of Mechanical Engineering
Professor Teng Li, Department of Mechanical Engineering
Professor Peter W. Chung, Department of Mechanical Engineering
Professor Derek Richardson, Department of Astronomy (Dean’s Representative)

Abstract: Terramechanics plays an important role in the design and control of robots moving on granular surfaces. Traction capabilities, slippage, and sinkage of a robot are governed by the interaction of a robot’s appendage (such as wheel, track or leg) with the operating terrain and how the terrain motion happens with respect to the appendage during such an interaction. In this dissertation work, dynamics of robot appendages interaction with granular media is explored by using numerical and experimental studies. A two dimensional (2D) numerical model constructed using the Discrete Element Method (DEM) is adapted to simulate lugged wheel interaction with granular media. Parametric studies on wheel performance are conducted for two different control schemes, namely, a slip-based control scheme and an angular velocity-based wheel control scheme. Furthermore, the soil flow pattern under the wheel is studied by examining the force distribution and evolution of force networks during the course of wheel travel.

An experiment setup is designed to study the particle motion and force networks inside the media during dynamic forcing. Two different designs of robot appendages, a lugged and a single actuator pendulum are investigated. High speed imaging of photo-elastic particles under polarized light is used to visualize the force distributions inside the media. Qualitative behavior of force chains/networks evolution during interaction with the lugged wheel and pendulum is presented. In addition, quantitative measures of the interaction between appendage and granular media, such as, the driving torque values, appendage velocity, and particle motion are inferred from the experimental findings.

Based on this work, insights can be gained into the design influences of robot appendages on performance and further understanding can be obtained on the behavior of granular media across different length scales. Furthermore, the numerical and experimental techniques developed and outcomes of this dissertation can serve as an important foundation for optimal design and control of different robot appendages interacting with deformable surfaces.