Browsing by Subject "Mechanical engineering"

Now showing 1 - 20 of 42

Aggregating VMT within predefined geographic zones by cellular assignment:a non GPS-based approach to mileage-based road use charging.
(2012-04) Davis, Brian James
Currently, most of the costs associated with operating and maintaining the roadway infrastructure are paid for by revenue collected from the motor fuel use tax. As fuel efficiency and the use of alternative fuel vehicles increases, alternatives to this funding method are being considered that don’t use fuel consumption as a surrogate for road use. Many systems have been proposed which are capable of assessing mileage based user fees (MBUF) based on the vehicle miles traveled (VMT) aggregated within predetermined geographic areas, or travel zones, in which the VMT is generated. Most of the systems capable of this use GPS. However, GPS has issues with public perception, commonly associated with unwanted monitoring or tracking and thus an invasion of privacy. One method to mitigate these issues is to use a system that utilizes a cellular network based approach that can determine a vehicle’s current travel zone, but does not determine a vehicle’s position through the use of GPS. The approach proposed here is based on a knearest neighbors (KNN) machine learning algorithm focused on the boundary of such travel zones. This method has two main phases. In phase one, the training phase, data is collected near zone boundaries using a cellular modem and a GPS receiver. This hardware creates a database that pairs readings consisting of observable cell towers and the strengths with which they were received, with the travel zone in which the reading took place, as determined by the GPS receiver. Then in phase two, the operational phase, GPS is no longer needed as the system detects changes in the vehicle’s travel zone by comparing currently available cellular information with the database. This method, while capable of determining the travel zone, is incapable of determining a vehicle’s precise location, which better preserves both the user’s actual privacy and perceived privacy. The work described here focuses on the design and evaluation of algorithms and methods that when combined, would enable such a system. The primary experiment performed evaluates the accuracy of the KNN algorithm at sample boundaries in and around the commercial business district (CBD) of Minneapolis, Minnesota. The results show that with the training data available, the algorithm can correctly detect when a vehicle crosses a boundary to within ±2 city blocks, or roughly ±200 meters. A means for handling this relatively small ambiguous region between travel zones is also presented. The findings imply that a cellular-based VMT system may indeed be a feasible method to aggregate VMT by predetermined geographic travel zones.
Analysis of the rigid porous manifold as an effevtive device to stratify solar thermal storage tanks.
(2011-07) Ghosh, Vivekananda
One of the most effective and simplest methods to maintain thermal stratification of solar hot water storage tanks during charge and discharge is the use of a rigid porous manifold. The same manifold design can be employed within a novel liquid desiccant solar thermal storage tank to prevent destruction of chemically stored energy during charge and discharge. This type of manifold does not require any moving parts or special materials and thus is particularly appealing for solar thermal storage systems. It has a series of vertical hydraulic resistance elements placed within a perforated tube. At the design operating conditions, the manifold ensures that fluid entering the tank is delivered to the vertical position where it is the same density as the tank fluid. In the present study the utility of a rigid porous manifold is assessed over a range of operating conditions in both a solar hot water and liquid desiccant storage environment. The primary result is the development of a simple relationship between a dimensionless performance indicator and a second dimensionless parameter that represents the operating condition. A simulation model is used to define this relationship between the operating condition and manifold performance and is applicable to manifolds operating in both hot water and liquid desiccant storage tanks. A plug flow tank model is used to approximate transient tank stratification. Initial modeling suggests off-design operation results in low levels of mixing. Finally, a manifold was built and tested within a prototype liquid desiccant tank. Results show that the design returns low density fluid through the bottom of the tank at a significantly reduced mixing rate compared to free discharge. The same manifold design is able to return high density fluid with minimal mixing.
Aquapod: the design of small amphibious tumbling robot.
(2012-06) Carlson, Andrew James
Battery-less wireless instrumented tibial tray.
(2011-11) Holmberg, James
Previous research has found that over 400,000 total knee replacement procedures (TKR) are annually performed in the United States. Therefore, it is important that the loads on TKR implants be fully understood to improve the reliability of the implants. This paper presents the development of a battery-less wireless instrumented tibial tray for TKR implants. Previous instrumented tibial trays were powered by inductive coupling which required the patient to wear an externally-powered coil. Whereas, the proposed instrumented tibial tray is powered internally by an integrated piezoelectric energy harvesting system. This paper also presents the development of capacitive force sensors and an ultra low-power method to measure the capacitive force sensors. Two capacitive force sensor designs were considered and neither design could meet all of the performance requirements for the intended application. Despite this finding, several sensors were produced to demonstrate the concept behind capacitive force sensing using piezoelectric energy harvesting. With a 316 lb applied force, the energy harvesting system could fully charge the storage capacitors in 11 steps and could harvest an average of 1051 μJ per step. To power the force measurement system for ten seconds and to transmit the data, the piezoelectric energy harvesting system must be charged before the force measurement process is initiated by a minimum of 11 steps with a force of 316 lbs and a minimum of two steps must be taken during the force measurement process. During the force measurement process, each force sensor was sampled at a frequency of 10 Hz for 10 seconds; thereafter, all of the data was transmitted to the RF base station. The resulting capacitive force sensors showed good results when a set of cyclic loads were applied; however, the sensors demonstrated issues with repeatability when the applied force was increased and then reduced to the original value. The force sensors require improvements, but once this is completed, the system shows promise to be an effective measurement device for TKR implants.
Bridging scales in modeling and simulation of thermal transport processes
(2014-08) Wheeler, Vincent Michael
The vastly disparate length and time scales existing in new devices and materials born out of nanotechnology have made thermal modeling and simulation more important and more difficult. The experimental thermal characterization of such systems, e.g. modern computer processors, can be prohibitively difficult or expensive making numerical simulation the only route to effective technology design. However, obtaining solutions that account for small scales, but are still computationally feasible, requires innovative modeling approaches. The research contained herein represents three independent contributions to the understanding of the modeling of thermal transport processes in systems with nano-sized features. At their common core, all contributions in this thesis are rooted in transport theory--the solution or approximation of the Boltzmann equation (BE)--to statistically describe a system made up of a great many energy-carrying particles. The work roughly divides into the three modes of heat transfer--convection, conduction, and radiation. First, a framework for the discretization of the BE (in its many forms) based on lattices is presented. The widely-used lattice Boltzmann method for the simulation of fluid flow is shown to be a sub-case. The framework gives a new rigorous foundation to the use of lattice methods which have emerged in recent years with applications ranging from Brownian motion to astrophysical radiation. Second, we give a thorough presentation of recently proposed models of heat conduction derived from the phonon BE which provides rigor and insight into the different approaches. Most notably, the "new heat equation" is derived directly from the phonon BE for the first time along with a novel boundary condition. The result is shown to give excellent agreement with the more detailed description provided by the equation of phonon radiative transport. Last, we provide the radiative characterization of a nano-porous material using Maxwell's equations in order to recover coefficients to the linear BE governing thermal radiative transfer.
Coupled theoretical and experimental methods to characterize heterogeneous, anisotropic, nonlinear materials: application to cardiovascular tissues
(2014-10) Witzenburg, Colleen M.
The Generalized Anisotropic Inverse Mechanics (GAIM) method is able to provide general tissue characteristics in terms of stiffness, anisotropy strength, and preferred orientation. It allows for the computational dissection of samples, capturing regional differences within a single sample nondestructively. However, the linear assumption implicit in GAIM limited its utility, particularly in the case of cardiovascular soft tissues, which exhibit markedly nonlinear behavior when operating at physiologic strain levels. Therefore, GAIM was extended to consider large-deformation kinematics, a nonlinear closed-form structural model of planar fibrous tissue mechanics was utilized to describe the nonlinear behavior of a cardiovascular soft tissue (rat ventricle wall), and the partitioning method utilized by GAIM was replaced with a more robust partitioning scheme. Then, GAIM was applied in a stepwise fashion (NGAIM) in order to capture the full nonlinear kinetics of cardiovascular soft tissues. Finally, experiments characterizing the three-dimensional loading and failure of healthy porcine ascending aorta were discussed. The work presented in this thesis marks the development and use of novel theoretical and experimental approaches for the analysis of complex cardiovascular soft tissues. An analysis method was developed, NGAIM, that can be applied to examine regional mechanical differences in planar, nonlinear, anisotropic, heterogeneous, tissue samples from all over the body which yields full-field stress. Finally, a partnering was proposed which exploits the characterization capacity of NGAIM with the predictive capacity of the multiscale model to create full three-dimensional simulations of cardiovascular soft tissue behavior.
Degradation Properties of Bioresorbable Material Candidates for Congenital Heart Defect Repair
(2013-08) Holst, Jessica Mae
The goal of this project is to investigate the use of bioresorbable materials for congenital heart defect repair. This investigation focused on the in vitro degradation over eight weeks of several biodegradable polymers including: Poly (L-lactide) or PLLA, 70:30 Poly (L-lactide)-Polycaprolactone or PLLA/PCL and Polyglycolide or PGA. Since surface area can affect degradation rates several morphologies of these polymers were included in the study such as knits, films, felts, electrospun materials and sponges. The degradation was characterized by: tensile testing, scanning electron microscope (SEM) visualization, differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). Results of these tests do not directly provide recommendation for specific materials for use as implantable, bioresorbable materials but they do confirm that the combination of chemical composition and material morphology significantly affect the degradation rate as measured by changes in molecular weight with time. This finding supports the possibility of fine tuning manufacturing processes of these materials to obtain a specific degradation profile. PLLA film material 3 was the only material tested that maintained its peak stress and peak strain behavior over the 8 week degradation time period. This does not necessarily rule out the other materials as long as they maintain mechanical integrity over the required time period. In addition, the changes in molecular weight (but not stress and strain behavior) over time were significantly affected by the type of degradation environment the material was placed in, static vs. agitated or dynamic. The importance of the degradation rate and mechanism for this application is extremely important so the inclusion of some form of agitation in future degradation experiments is recommended. Finally, the degradation environment in this experiment was relatively inert and testing with digestive enzymes or other blood components is also recommended.
Design and construction of a hydrostatic dynamometer for testing a hydraulic hybrid vehicle.
(2012-07) Kohring, Henry Julian
A hydrostatic dynamometer has been constructed to test a hydraulic hybrid passenger vehicle. Hybrid vehicles reduce their fuel consumption by capturing energy normally lost during braking and reusing it during acceleration in addition to managing the engine to enable it to run at a higher efficiency operating point. The dynamometer is designed to test a particular hybrid vehicle which stores and transmits energy hydraulically. Measurement of fuel consumption while the vehicle completes standard drive cycles is necessary to refine and validate the performance and efficiency of the vehicle. The dynamometer provides repeatable, convenient, inexpensive, safe, and flexible indoor testing for the vehicle. The dynamometer connects directly to the output shaft of the vehicle's transmission. It is mounted on a bedplate installed behind the vehicle. The dynamometer's hydraulic pump loads or motors the vehicle to simulate driving. It can be controlled either manually or automatically. Automatic controls allow the dynamometer to calculate and apply the appropriate load based on vehicle speed. MATLAB and Simulink simulations aided the design of the dynamometer. A MATLAB simulation of the vehicle determined torque and speed requirements for standard drive cycles. Another MATLAB simulation calculated pressures, flow rates, and energy storage requirements on the dynamometer to size components. A Simulink simulation aided controls development. The dynamometer has demonstrated open and closed loop performance with and without load. It has demonstrated fast torque tracking. However, vehicle reliability issues have prevented drive cycle tests from being completed.
The design and experimental investigation of an alumina reticulate porous ceramic heat exchanger for high temperatures
(2014-06) Banerjee, Aayan
The present study focuses on the design, modeling and testing of an alumina heat exchanger filled with reticulate porous ceramic (RPC). The heat exchanger has been designed to operate reliably at temperatures up to 1773 K, integrate seamlessly with the reactor designed for isothermal CO2 and H2O splitting using ceria and obtain an effectiveness of >0.85 for the range of flow rates anticipated during operation of the isothermal reactor. The RPC morphology, namely porosity and pore density and the geometry of the heat exchanger are selected based on the results of a fluid flow and heat transfer model of the heat exchanger. A prototype was also tested at temperatures up to 1240 K. The permeability, inertial coefficient, overall heat transfer coefficient, effectiveness and pressure drop were measured.
Design and experimental investigation of rotational angle based tracking control
(2014-08) Yang, Meng
This work investigates the tracking control in the rotational angle domain based on the time-varying internal model principle. The focus is to enable precise, reliable and computational efficient output tracking/disturbance rejection in the angle domain. To achieve better performance, existing approaches typically require more discrete samplings per revolution, which can drastically increase the controller order and also poses challenge for the stabilizer convergence. To address those issues, a varying sampling interval approach is proposed, where the control sampling rate is not fixed but optimized based on errors between sampling points, so that proper regulation performance can be achieved without significantly increasing the number of sampling points. Meanwhile, to improve the convergence rate of the tracking error, additional LMI constraints are added to the existing stabilizer synthesis. Through experimental study on a camless engine valve actuation system, the effectiveness of the proposed approaches is well demonstrated.
Development of a piezoelectric weigh-in-motion system for battery-less wireless operation.
(2011-08) Pruden, Sean Michael
Roads are among the most important pieces of a nation’s infrastructure. To ensure the continued use of these systems they must be monitored and understood using various technologies. A weigh-in-motion (WIM) system is one such device which is used to obtain traffic flow and vehicle weight data. This sensor monitors all traffic traveling over a stretch of road without requiring the vehicles to stop for measurement. As a result, it can be used to reduce the number of overloaded trucks through enforcement of weight requirements. This will create a safer driving environment, prolong road life, and reduce maintenance costs. The largest deterrent to implementing current weigh-in-motion technologies is the large costs incurred through purchase, installation, and maintenance. In addition, these systems currently require wires to be routed through the road pavement for the purpose of data travel and power. This paper focuses on the creation of a low cost WIM sensor being developed for the addition of battery-less wireless implementation in the future. Such a system would allow for broader use of the technology and reduce the aforementioned problems caused by overloaded trucks. The final product would not only reduce costs due to road damage but also those costs associated with sensor maintenance. There are many challenges associated with the practical design of a WIM system. First, this system must be large enough to contain the full contact patch of the largest operating vehicle on the road while preventing this design from yielding under vehicle weight. Second, the sensor must be as accurate or more accurate than current WIM technologies under all operating conditions. Finally, it must have a simple and cost effective construction. In the design of such a sensor, the author implemented a two layer design to reduce the number of piezo-electric patches and thus obtain an inexpensive system. The top layer was a frame large enough to bear the weight of the full contact patch of the vehicle. The lower beams served as a mounting location for the piezos. Both layers had to withstand the full weight of the dynamic vehicle load without yielding. The design process also included resonant frequency analysis to understand if the vehicle velocity would cause a change in output of the sensor. Finally, electronics had to be developed to monitor, store, and reset piezo readings for continued operation. In addition to the aforementioned challenges, finding the means to test such a piece of equipment was extremely difficult. First, a stretch of road had to be identified which could be modified for the installation of the sensors. Equipment had to be procured to cut and remove concrete, and pour a new slab before sensor testing could begin. Additionally, vehicles of various weights had to be obtained and a driver found certified to drive them in order to test the equipment at multiple speeds. Finally, this construction and testing had to be completed during the winter outside.
Development of self-powered wireless structural health monitoring (SHM) for wind turbine blades
(2015-01) Lim, Dongwon
Wind turbine blade failure can lead to unexpected power interruptions. Monitoring wind turbine blades is important to ensure seamless electricity delivery from power generation to consumers. Structural health monitoring (SHM) enables early recognition of structural problems so that the safety and reliability of operation can be enhanced. This dissertation focuses on the development of a wireless SHM system for wind turbine blades.The sensor is comprised of a piezoelectric energy harvester (EH) and a telemetry unit. The sensor node is mounted on the blade surface. As the blade rotates, the blade flexes, and the energy harvester captures the strain energy on the blade surface. Once sufficient electricity is captured, a pulse is sent from the sensing node to a gateway. Then, a central monitoring algorithm processes a series of pulses received from all three blades. This wireless SHM, which uses commercially available components, can be retrofitted to existing turbines.The harvested energy for sensing can be estimated in terms of two factors: the available strain energy and conversion efficiency. The available strain energy was evaluated using the FAST (Fatigue, Aerodynamics, Structures, and Turbulence) simulator. The conversion efficiency was studied analytically and experimentally. An experimental set-up was designed to mimic the expected strain frequency and amplitude for rotor blades. From a series of experiments, the efficiency of a piezoelectric EH at a typical rotor speed (0.2 Hz) was approximately 0.5%. The power requirement for sending one measurement (280 $\mu$J) can be achieved in 10 minutes. Designing a detection algorithm is challenging due to this low sampling rate. A new sensing approach-the timing of pulses from the transmitter-was introduced. This pulse timing, which is tied to the charging time, is indicative of the structural health. The SHM system exploits the inherent triple redundancy of the three blades. The timing data of the three blades are compared to discern an outlier, corresponding to a damaged blade. Two types of post-processing of pulses were investigated: (1) comparing the ratios of signal timings (i.e. transmission ratio); and (2) comparing the difference between signal timings (i.e. residuals). For either method, damage is indicated when the energy ratio or residual exceeds a threshold level. When residuals are used to detect damage, performance measures such as the false alarm rate and detection probability can also be imposed. The SHM algorithms were evaluated using strain energy data from a 2.5 MW wind turbine.
Dynamic response of structural elements undergoing moving loads and thermal strains using finite elements
(2014-12) Paganelli, Anthony
Many structures undergo forced vibration due to moving loads: bridges, railway and subway tracks, aircraft carrier decks, etc. Many of these structures are also subjected to various types of thermal loading. Currently, there are limited or no analytical or experimental methods for analyzing the combined effects of the mechanically induced vibrations and thermal loads on complicated structures such as plates and curved beams with moving loads. Instead, it is more preferable to analyze such problems by numerically discretizing the spatial portion of the equations of motion using Finite Elements and the temporal portion with a numerical time stepping algorithm. The preferred time discretization method presented here is the GSSSS framework of algorithms in conjunction with the Finite Element method. This research will focus on: 1.) Developing a procedure for solving the dynamic response of structures undergoing forced vibration due to moving loads, 2.) Applying this procedure to curved beam structures, and 3.) Analyzing effects of the moving loads and thermal loads on the combined dynamic response of curved beams and flat plates. These developments provide a baseline for future research in the areas of combined transient thermo-mechanical problems using the GSSSS family of algorithms.
Effect of cell attachment and molecular events associated with freezing biophysics and the "two factor" injury hypothesis.
(2011-12) Balasubramanian, Saravana Kumar
Freezing of biological systems is generally intended to maximize cell survival (cryopreservation) or injury (cryosurgery) depending on the application. The biophysical contribution to cellular freeze injury is generally described by the “two factor” injury hypothesis. Slow freezing is associated with “solution effects” injury while rapid freezing is linked to the lethality of intracellular ice formation (IIF). The “two factor” hypothesis has been actively investigated for cell suspensions. While cell suspensions provide a fundamental understanding of cellular biophysics and injury, more complex systems (featuring cell attachment) are needed to potentially link to tissues. The effect of cell attachment in the context of the “two factor” hypothesis has not been extensively investigated especially for water transport biophysics. In addition, the “two factor” injury hypothesis implicates changes to cellular macromolecules (e.g. lipids and proteins) as potential freezing injury mechanisms. Currently very little is known about the molecular events associated with the biophysics of freezing cells. The specific aims (SA) of the dissertation are listed below, and it addresses some of the limitations identified. SA 1: Study the effect of cell attachment on the “two factor” hypothesis during freezing SA2: Investigate the molecular events (lipids and proteins) associated with the “two factor” biophysics of freezing The effect of cell attachment (SA 1) was studied using two mammalian cell types – human dermal fibroblasts (HDF), and porcine smooth muscle cells (SMC). The cellular systems that were evaluated include suspensions, monolayer (cell-cell interactions), and tissue equivalents (cell-cell and cell-ECM interactions). Cell based biophysical models were then used to compare the predicted biophysics as a function of the attachment state. The molecular events associated with the “two factor” biophysics (SA 2) were studied using three different mammalian cell types – HDF, SMC, and human LNCaP prostate tumor cells. Changes to membrane lipids and proteins during controlled freezing were evaluated using Fourier Transform Infra-Red spectroscopy (FTIR). The molecular events were then linked to cellular freezing biophysics assessed using cryomicroscope. The important findings of this dissertation are included below: 1. Cell attachment affects the “two factor” biophysics of freezing. Experimental data shows that IIF is enhanced for cells in the attached state as compared to suspensions. In addition, the results suggest that water transport is enhanced for cells in the attached state as compared to suspensions. However, the impact of increased water transport on cell survival for attached cells is unclear. 2. The study of molecular events shows that slow freezing affects membrane phase transition (liquid crystalline to gel phase), whereas rapid freezing is observed to maintain the high conformational disorder of the membranes. 3. Molecular events (i.e. membrane phase transition) measured using FTIR are linked to cellular biophysics measured using cryomicroscope. 4. The results show a link between cell and lipid membrane dehydration events. It is suggested that membranes can only tolerate dehydration to a certain extent. This connection is suggested as a potential link to a molecular mechanism of cell injury due to “solution effects”.
The effect of ethanol-water fumigation on the performance and emissions from a direct-injection diesel engine.
(2010-09) Olson, André Louis
The effect of ethanol fumigation and water injection on the performance and exhaust emissions from a 1.9-liter Volkswagen TDI diesel engine was investigated. The engine tests were conducted at a speed of 1700 rpm, and at loads of 40, 80, and 120 N-m. One hundred-proof ethanol, 200-proof ethanol, and distilled water were used as fumigants; they were injected into the intake air through a single air-atomizing nozzle mounted in the engine's intake manifold. Two flowrates of fumigant were used: 25% and 40% of the volumetric diesel fuel flowwrate at the corresponding baseline operation. The atomizing nozzle was mounted either downstream or upstream of the aftercooler, and it was found that the upstream configuration resulted in more consistent results- probably due to improved evaporation and mixing of the fumigant with the intake air. In general, when compared to baseline operation, both ethanol and water resulted in reductions in the emissions of NOx, total particle number, and total particle volume concentrations. At 1700 rpm and 80 N-m, the most significant (up to 25%) reductions in NOx emissions were obtained with water injection, whereas ethanol resulted in more pronounced reductions in total particle number (about 40%) and total particle volume concentrations (about 30%). The HC emissions were dramatically increased with ethanol fumigation, particularly with 200-proof ethanol. The brake thermal efficiency was slightly decreased with both proofs of ethanol. As far as the emissions of NOx and PM are concerned, the fumigation of 100-proof ethanol yielded better results than the fumigation of 200-proof ethanol.
The Effects of turbulence on metal nanoparticle nucleation in turbulent jets.
(2011-08) Fager, Andrew Jamison
The effects of turbulence on nanoparticle nucleation are studied using a combination of fully resolved and large-scale quantities from direct numerical simulations. A size de- pendent model for homogeneous nucleation captures the formation of zinc nanoparticles. Growth of these particles is considered by Brownian coagulation. Three simulations are performed using a single Reynolds number and vapor mass-fraction. In one simulation nucleation is computed with fully-resolved data while the remaining two compute nu- cleation with large-scale filtered data, each at different filter-widths. In all simulations fluid and scalar quantities are fully resolved. A nodal method captures the resultant particle field, approximating the general dynamic equation. Comparisons between the three simulations are made in order to asses the role small-scale turbulent features play on nucleation. Results show that nucleation occurs primarily along the shear layers. Unresolved subgrid-scale nucleation acts to both increase and decrease nucleation. The predominant effect is to decrease nucleation. This leads to an over-prediction of nucle- ated particles when neglecting the small-scales. The over-prediction is largest in laminar and transitional flow regimes and increases with filter width. No significant discrepan- cies are seen in the size of nucleated particles when using large-scale quantities.
Energy conversion using phase transformation in multiferroic materials
(2013-08) Song, Yintao
The history of using first order phase transformations to convert heat into other forms of energy stretches back as far as the 1600's, when the first steam engine was invented. This method can be further applied to any first order phase transformation beyond the liquid-vapor systems. Multiferroic materials undergoing phase transformations, during which a ferroic property changes drastically, are promising candidates, especially in the small temperature difference regime. In this thesis I investigate the conversion from heat into electricity by this new method. A family of alloys undergoing martensitic phase transformation with a big change of magnetization is demonstrated to be capable of energy conversion. It is shown by construction of a demonstration that the proposed concept is feasible. Also the idea of using a temperature gradient for this new energy conversion method is examined. The analysis shows that it is possible to convert a temperature gradient to a temperature oscillation by automatically moving the specimen in two conservative force fields: gravity and magnetic field. Quasi-static and finite-time thermodynamic models are developed. Based on the models, the efficiency and power output of this new method is evaluated theoretically, and the directions of design improvement are proposed. The Clausius-Clapeyron relation (the effect of magnetic field on the transformation temperature) is found to be a key thermodynamic relation in this method. The utilization of other types of muliferroic phase-transforming materials is surveyed.
Fluid modeling and design of gas channels of solar non-stoichiometric redox reactor
(2014-02) Kedlaya, Aditya
The present numerical study in FLUENT analyzes the fluid flow field within a solar powered reactor designed for syngas production. The thermochemical reactor is based on continuous cycling of cerium oxide (ceria) in a non-stoichiometric reduction/oxidation cycle. The reactor uses a hollow cylinder of porous ceria which rotates through a high-temperature zone, by exposure to concentrated sunlight and partially reduced in an inert atmosphere due to flow of the sweep gas (N2), and then through a lower temperature zone where the reduced ceria is re-oxidized with a flow of CO2 and/or H2O, to produce CO and/or H2. In terms of fluid flow modeling, the issue of crossover of species (leakage) within the reactor is critical for proper functioning of the reactor. The first part of the work relates to the geometry and placement of the inlet/outlet gas channels for the reactor optimized to minimize crossover of the species. This is done by conducting a parametric study of geometric variables associated with the inlet/outlet geometry. A simplified 2D fluid flow reactor model which incorporates multi-species flow is used for this study. Further, 2D and 3D reactor models which capture the internal structure more accurately are used to refine the inlet/outlet design. The optimized reactor model is found to have an O2 crossover of 2%-6% and oxidizer crossover of 8%-21% at different flow rates of the sweep gas and the oxidizer studied.In the second part of the work, the reactor model is simulated under varying test conditions. Different working conditions include morphologies of the reactive material, rotational speed of the ceria ring and the recuperator, flow rates of sweep gas and the oxidizer, types of oxidizer (CO2, H2O). The 3D reactor model is also tested using one, two and three discrete inlet/outlet ports and compared with slot configuration
Heat transfer to droplets in developing boundary layers at low capillary numbers
(2014-08) Wenzel, Everett
This thesis describes the heating rate of a small liquid droplet in a developing boundary layer wherein the boundary layer thickness scales with the droplet radius. Surface tension modifies the nature of thermal and hydrodynamic boundary layer development, and consequently the droplet heating rate. A physical and mathematical description precedes a reduction of the complete problem to droplet heat transfer in an analogy to Stokes' first problem, which is numerically solved by means of the Lagrangian volume of fluid methodology.For Reynolds numbers of order one, the dispersed phase Prandtl number significantly influences the droplet heating rate only in the transient period when the thermal boundary layer first reaches the droplet surface. As the dispersed phase Prandtl number increases, so does the duration of the transient. At later times, when the the droplet becomes fully engulfed by the boundary layer, the heating rate becomes a function of only the constant heat flux boundary condition. This characteristic holds for all Peclet and Weber numbers, but the spatial behavior of the droplet differs for small and large Peclet and Weber numbers.Simulation results allow for the development of a predictive tool for the boiling entry length of dilute systems in channel flow. The tool relies on an assumption of temperature equivalency between the droplet and the thermal boundary layer evaluated in absence of the dispersed phase, which is supported by the computational results. Solutions for plug and fully developed flow do not differ appreciably, suggesting a precise description of the fluid mechanics is not necessary for an approximation of the boiling entry length. Future experimental work is required to validate the predictive models derived in this thesis.
Heterogeneous protein distribution during rapid and equilibrium freezing
(2013-04) Twomey, Alan Michael
Interactions between proteins and ice were studied in situ using FTIR and confocal Raman microspectroscopy under equilibrium and non-equilibrium conditions over a range of temperatures. During quasi-equilibrium freezing of aqueous solutions of dimethyl sulfoxide (DMSO) and bovine serum albumin, preferential exclusion of albumin and/or DMSO was observed. It was hypothesized that the albumin may be adsorbed onto the ice interface or entrapped in the ice phase. To investigate protein-ice interactions during freezing under non-equilibrium conditions, confocal Raman microspectroscopy was used to map the distribution of albumin and the cryoprotective agent trehalose. Microheterogeneity was found in the composition of the freeze-concentrated liquid phase that indicated that albumin was preferentially distributed near or at the boundary of the ice phase. The observed microheterogeneity did not occur under all freezing protocols, which suggests that the technique developed here could be used to develop freezing protocols that would reduce harmful protein-ice interactions.

University Digital Conservancy

Browse by Subject

Browsing by Subject "Mechanical engineering"