Defenses

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.

Title: Additive Manufacturing of Microfluidic Technologies via In Situ Direct Laser Writing

Day/Time: Thursday Feb 11th 2021, 10:45am-12:45pm

Examining Committee:
Ryan Sochol (Chair)
Don DeVoe
Eleonora Tubaldi
Axel Krieger
Reza Ghodssi (Dean’s Represenative)

Abstract: Innovations in microfluidic technologies hold great promise for a wide range of chemical, biomedical, and soft robotic applications. Unfortunately, key drawbacks associated with soft lithography-based microfabrication processes hinder such progress. To address these challenges, we advance a novel submicron-scale additive manufacturing (AM) strategy, termed “in situ direct laser writing (isDLW)”. IsDLW is an approach that benefits from the architectural versatility and length scales inherent to two-photon polymerization (2PP), while simultaneously supporting the micro-to-macro interfaces required for its effective utilization in microfluidic applications. In this dissertation, we explore isDLW strategies that enable passive and active 3D microfluidic technologies capable of enhancing “on-chip” autonomy and sophistication. Initially, we use poly(dimethylsiloxane) (PDMS)-based isDLW to fabricate microfluidic diodes that enable unidirectional rectification of fluid flow. We introduce a novel cyclic olefin polymer (COP)-based isDLW strategy to address several limitations related to structural adhesion and compatibility of PDMS microchannels. We use this COP-based approach to print microfluidic transistors comprising flexible and free-floating components that enable both “normally open” (NO) and “normally closed” (NC) functionalities—i.e., source-to-drain fluid flow (Q_SD) through the transistor is either permitted (NC) or obstructed (NO) when a gate input (P_G) is applied. As an exemplar, we employ COP-based isDLW to print an integrated microfluidic circuit (IMC) comprised of soft microgrippers downstream of NC microfluidic transistors with distinct P_G thresholds. All of these microfluidic circuit elements are printed within microchannels ≤40 μm in height, representing the smallest such components (to our knowledge). Theoretical and experimental results illustrate the operational efficacy of these components as well as characterize their performance at different input conditions, while IMC experimental results demonstrate sequential actuation of the microrobotic components to realize target gripper operations with a single P_G input. Furthermore, to investigate the utility of this strategy for static microfluidic technologies, we fabricate: (i) interwoven bioinspired microvessels (inner diameters<10μm) capable of effective isolation of distinct microfluidic flow streams, and (ii) deterministic lateral displacement (DLD) microstructures that enable continuous sorting of submicron particles (860 nm). In combination, these results suggest that the developed AM strategies offer a promising pathway for advancing state-of-the-art microfluidic technologies for various biological and soft robotic applications

Title: ADVANCED ABSORPTION MATERIALS AND THEIR APPLICATION IN REFREGIATION

Date/Time: January 12, 2021 2:00PM – 4:00PM

Committee:
Prof. Bao Yang (Chair)
Prof. Amir Riaz
Prof. Peter B. Sunderland
Prof. Teng Li
Prof. Chunsheng Wang (Dean Representative).

Zoom Link: https://umd.zoom.us/j/94210112455?pwd=MjVWRS9TVXR4cENFb2t3aTlTR0ljUT09

Abstract: Absorption chillers, which utilize heat as the primary energy input, have been considered a more environment-friendly alternative to vapor-compression cooling systems. The thermodynamic properties of absorbent generally limit the performances of absorption chillers. In the first part of the dissertation, a new method to determine the molecular interaction energies is developed. The molecular interaction energies can be related to many macroscopic thermodynamic properties, such as desorption heat and hygroscopicity. From the studies on ionic liquid absorbents, it is found that a shorter alkyl group in anion would produce higher interaction energy with water, thus increasing the hygroscopicity. In contrast, the fluorination of anion would reduce its interaction energy with water, thus reducing the hygroscopicity. A new formula is also developed using interaction energies to predict the desorption heat of absorbents, which is an essential parameter for evaluating absorbent performances. The second part of the dissertation focuses on the development of a microemulsion-based absorption chiller consisting of an electrostatic desorber, a nozzle-based absorber and an evaporator. Due to the tiny droplet size, it is thermodynamically challenging to regenerate the absorbed water in a liquid form from a microemulsion state. The electrostatic desorber would first utilize heat to transform the microemulsion absorbent into a macroemulsion state. The voltage is then applied to the absorbent to expedite the regeneration. Therefore, the electrostatic desorber can regenerate the absorbed water in a liquid form, which eliminates the latent heat requirement, offering the potential to improve energy efficiency. Inspired by the honeycomb shape, electrodes in the desorber are arranged in a multi-hexagon pattern, enabling a large desorber volume without increasing the voltage amplitude. The potential cooling power is improved by over 50 times compared to the original single-electrode desorber. The nozzle-based absorber&evaporator system utilizes nozzles to generate microemulsion absorbent and water in small droplet size to enhance the absorption and evaporating process.  Combining the electrostatic desorber and the absorber&evaporator system, the complete absorption chiller could run continuously and achieve a cooling power of about 100 W.

DEVELOPMENT OF COOLING SYSTEMS WITH ACTIVE ELASTOCALORIC REGENERATORS

Date/Time: Tuesday, December 15^th of 2020, 3:30 PM EST

List of committee members

• Professor Reinhard Radermacher, Chair
• Professor Ichiro Takeuchi
• Professor Yunho Hwang
• Professor Olivier Bauchau
• Professor Marino di Marzo
• Professor Bao Yang
• Chun-cheng Piao, Ph.D.

Zoom or Webex Link: https://umd.zoom.us/s/98205535196

Abstract: The vapor compression cycle (VCC) has been developed and optimized over a century to provide cooling in buildings (residential and commercial) and vehicles. However, its usage has resulted in unpredicted environmental damage such as depleting the ozone layer and promoting global warming when the refrigerant fluid leaks into the atmosphere. Because of this, it is important to develop a superior technological alternative without the environmental costs. One way to tackle this problem is to develop heat pumping cycles using solid-state refrigerants: a solid is incapable of leaking into the atmosphere. Yet, a solid-refrigerant cannot flow to deliver cooling the same way a refrigerant-fluid does. This required a system conceptual redesign, which started with near-room temperature cooling with magnetocaloric materials in 1976 and elastocaloric materials in 2012.

The ability of the cooling system to pump heat across a large temperature span is called the “temperature lift”. The amount of heat the system can absorb while maintaining that temperature lift is called the “cooling capacity”. An effective way to develop these technical capabilities is first to achieve a large temperature lift and second to increase cooling capacity to match the requirements.

In his work four different system configurations were studied with the following objectives: maximizing the temperature lift of the system and measuring the cooling capacity. During the process, new challenges were identified and addressed. The first configuration was based on the thermal-wave heat recovery strategy, while the other three were a 1-stage, 2-stage and reciprocating variants of the active regeneration cycle.

From the studied configurations the thermal-wave-based cycle achieved a low temperature lift of 8K, at large average strain of 4.5%, and the largest cooling capacity of 120W. Active regeneration-based cycles achieved the largest temperature lift of 21.3K, at a low average strain of 3.5%, but a low cooling capacity of between 16 and 25W. This dissertation shows there is a fundamental limitation in active regeneration cycles applied to single composition elastocaloric materials that limits the maximum applicable average strain, which in turn affects the cooling capacity. Different alternatives to address this issue, as well as suggestions to improve the overall thermal and structural performance of the system are reviewed.

Title: Underfill Selection to Improve Solder Joint Reliability For Down Hole Drilling Applications

Author: Sriram Jayanthi

Date/Time: November 19, 2020 10:00am-12:00pm

Examining Committee:

• Professor Patrick McCluskey, Chair
• Professor Abhijit Dasgupta
• Dr. Michael Azarian

Abstract: Underfill materials were originally developed to improve the solder joint reliability of the BGA packages under the thermal cycling when they are experiencing stresses due to the CTE mismatches between the board and the component. Although it is stated that the underfills will improve the shock reliability of the solder joints under the harsh environment for automobiles and military applications (-40 to 125oC). It has been found in the thermal cycling conditions the underfills will reduce the life of the solder balls. All the studies that had been performed were mostly below 150oC. There are no certain guidelines for selecting the underfills with the properties of the materials.  The main aim of this research is to create a guideline for selecting the underfills for high-temperature applications (above 150oC) for different BGA packages. In the first section, initial characterization and benchmarking of the underfills that are available in the industry was performed. In the second section, all the selected underfills were subjected to a harsh environment to find failure modes and mechanisms. With the help of experimentation and FEA that was done, guidelines were created for selecting the underfills for different BGA packages. This will be helpful to oil & gas and military applications.

Title: Physics-Based and Data-Driven Modeling of Hybrid Robot Movement on Soft Terrain

Author: Guanjin Wang

Advisory Committee:

• Professor Balakumar Balachandran, Chair & Advisor
• Associate Professor Amir Riaz (Co-Advisor)
• Professor Teng Li
• Professor Amr Baz
• Professor Peter Chung
• Professor Derek Richardson (Dean’s Representative)

Date & Time: November 13, 2020 2pm-4pm

Abstract: Navigating the unmapped environment is one of the ten biggest challenges facing the robotics community. A vision-based navigation system embedded in the mobile robot can only help to negotiate obstacles, which are well described by geometrical features, like sharp-edged stones and rocks.  Other aspects like sand, snow, and challenging terrains, are challenges for motions that robots cannot avoid during missions. Thus, designing and selecting effective gaits to navigate over terrains that may not be well describable by geometry is crucial for robot exploration. Wheeled robots can move fast on flat surfaces but suffer from loss of traction and immobility on soft ground. However, legged machines have superior mobility over wheeled locomotion when they are in motion over flowable ground or a terrain with obstacles but can only move at relatively low speeds on flat surfaces. A question is: If legged and wheeled locomotion are combined, can the resulting hybrid leg-wheel locomotion enable fast movement in any terrain condition?

Investigations into vehicle terrain interaction fall in the area of terramechanics. Traditional terra-mechanics theory can help capture large wheel vehicle interaction with the ground. However, legged or hybrid locomotion on a granular substrate is difficult to investigate by using classical empirical terra-mechanics theory due to sharp-edge contact. Recent studies show the continuum simulation can serve as an accurate tool for simulating dynamic interactions with granular material at laboratory and field scales. Therefore, to investigate the rich physics during dynamic interactions between the robot and the granular terrain, a computational framework based on the Smooth particle hydrodynamics (SPH) method has been developed and validated by using experimental results for single robot appendage interaction with the granular system. This framework has been extended and coupled with a multi-body simulator to model different robot configurations. Encouraging agreement is found amongst the numerical, theoretical, and experimental results, for a wide range of robot leg configurations, such as curvature and shape. The sensitive dependence of robot performance on different gaits has been investigated by parametric space exploration.

The above mentioned physics-based simulation can serve as a high-fidelity tool to uncover clues about the underlying mechanism of dynamic interactions between robots and soft terrain. However, real-time navigation in a challenging terrain requires fast prediction of the dynamic response of the robot, which is useful for terrain identification and robot gait adaption. Therefore, a data-driven modeling framework has also been developed for the fast estimation of the slippage and sinkage of robots. The data-driven model leverages the high-quality data generated from the offline physics-based simulation for the training of a deep neural network founded on long short-term memory (LSTM) cells. The results are expected to form a good basis for online robot navigation and exploration in unknown and complex terrains.

Title: Reduction of Mixture Property Variation Through Control on Initial Mixing Dynamics

Author: Marcelo Arispe-Guzman

Date/Time: November 20, 2020 9:00am-11:00am

Examining Committee:
Professor David Bigio, Chair
Professor Balakumar Balachandran
Professor Peter Chung
Professor Ryan Sochol

Zoom Link: https://umd.zoom.us/j/5898885184

Abstract: Blend homogenization of a liquid-solid mixtures is achieved through mixer agitation which disperses the liquids and breaks up the agglomerates. Creating energetic or pharmaceutical blends requires a very low degree of mixture variation in the final product. Initial solid-liquid feeding protocols into the mixer greatly affect the ability to achieve low variation at minimal energy input. Experiments in a vertically oscillating mixer using dyed silicon oil and glass beads examined the effect of feed protocols, while varying acceleration and the number of cycles. A Central Composite Design (CCD) DOE revealed that the percent homogeneity and coefficient of variation measures of mixing are linearly dependent on acceleration and number of cycles. Experimental observations lead us to redefine the model for breakup of wet agglomerates. This study offers a starting point to developing feed protocols to improve the efficiency of oscillating mixers, such as the resonant acoustic mixer (RAM), for liquid-solid mixing.

Title: INTERFACE OF IN-SITU ADDITIVE MANUFACTURING AND PHASE CHANGE LIQUID METALS TO OPTIMIZE HIGH THERMAL DENSITY PROBLEM IN SPACECRAFT AVIONICS STRUCTURES

Author: Jerald Armen

Date/Time: November 6, 2020 – 1:00pm-3:00pm

Zoom Link: https://umd.zoom.us/j/6589422509?pwd=em1PbXRVRTNvaldSVkNHejl0NFRFUT09

Examining Committee:

• Professor Hugh Bruck, Chair
• Professor Abhijit Dasgupta 
• Professor David Bigio
• Professor Ryan Sochol
• Professor Kyu Yong Choi (Dean’s Representative)