This work focuses on an innovative Rotary Displacer SE (RDSE) configuration for Stirling engines (SEs). RDSE features rotary displacers instead of reciprocating displacers (found in conventional SE configurations), as well as combined compression and expansion spaces. Guided by the research question "can RDSE as a novel configuration achieve a higher efficiency compared to conventional SE configurations at comparable operating conditions?", the goal of this study is to characterize, analyze, and optimize RDSE which is pursued in three technical stages. It is observed the RDSE prototype has an optimum phase angle of > 90° and thermal efficiency of 15.5% corresponding to 75.2% of the ideal (Carnot) efficiency at the source and sink temperatures of 98.6° C and 22.1° C, respectively. Initial results indicate that 125° phase angle provides more power than that of the theoretically optimum 90° phase angle. The results also show comparable B_n and significantly higher W_n values (0.047 and 0.465, respectively) compared to earlier studies, and suggest the RDSE could potentially be a competitive alternative to other SE configurations. Furthermore, due to lack of a regenerator, the non-ideal effects calculated in the analytical approach have insignificant impact (less than 0.03 kPa in 100 kPa). The clearance volume in …

This work investigates the Fresnel-lens-based solar concentrator-receiver system in a multi-perspective manner to design, test and fabricate this concentrator with high-efficiency photon and heat outputs and a minimized effect of chromatic aberrations. First, a MATLAB®-incorporated algorithm optimizes both the flat-spot and the curved lens designs via a statistical ray-tracing methodology of the incident light, considering all of its incidence parameters. The target is to maximize the solar ray intensity on the receiver's aperture, and therefore, achieve the highest possible focal flux. The algorithm outputs prismatic and dimensional geometries of the Fresnel-lens concentrator, which are simulated by COMSOL® Multiphysics to validate the design. For the second part, a novel genetically-themed hierarchical algorithm (GTHA) has been investigated to design Fresnel-lens solar concentrators that match with the distinct energy input and spatial geometry of various thermal applications. Basic heat transfer analysis of each application decides its solar energy requirement. The GTHA incorporated in MATLAB® optimizes the concentrator characteristics to secure this energy demand, balancing a minimized geometry and a maximized efficiency. Two experimental applications were selected from literature to validate the optimization process, a solar welding system for H13 steel plates and a solar Stirling engine with an aluminum-cavity receiver attached to the …

In this study, gas sensing systems that are based on piezoelectric smart material and structures are proposed, designed, developed, and tested, which are mainly aimed to address the temperature dependent CO2 gas sensing in a real environment. The state-of-the-art of gas sensing technologies are firstly reviewed and discussed for their pros and cons. The adsorption mechanisms including physisorption and chemisorption are subsequently investigated to characterize and provide solutions to various gas sensors. Particularly, a QCM based gas sensor and a C-axis inclined zigzag ZnO FBAR gas sensor are designed and analyzed for their performance on room temperature CO2 gas sensing, which fall into the scope of physisorption. In contrast, a Langasite (LGS) surface acoustic wave (SAW) based acetone vapor sensor is designed, developed, and tested, which is based on the chemisorption analysis of the LGS substrate. Moreover, solid state gas sensors are characterized and analyzed for chemisorption-based sensitive sensing thin film development, which can be further applied to piezoelectric-based gas sensors (i.e. Ca doped ZnO LGS SAW gas sensors) for performance enhanced CO2 gas sensing. Additionally, an innovative MEMS micro cantilever beam is proposed based on the LGS nanofabrication, which can be potentially applied for gas sensing, when combined with …

In this study, a series of denim fiberboards are fabricated using two different resins, malamine urea formaldehyde (MUF) and polymeric methylene diphenyl diisocyanate (pMDI). Two experimental design factors (1) adhesive content and (2) MUF-pMDI weight ratio, were studied. All the denim fiberboard samples were fabricated following the same resin blending, cold-press and hot-press procedures. The physical and mechanical tests were conducted on the fiberboard following the procedures described in ASTM D1037 to obtain such as modulus of elasticity (MOE), modulus of rupture (MOR), internal bond (IB), thickness swell (TS), and water absorption (WA). The results indicated that the MOE was significantly affected by both factors. IB was affected significantly by weight ratio of different glue types, with 17 wt% more MDI resin portion in the core layer of the denim boards, the IB for total adhesive content 15% fiberboard was enhanced by 306%, while for total adhesive content 25% fiberboard, enhanced by 205%. TS and WA, with higher adhesive content used in denim boards' fabrication, and more pMDI portion in the core layer of the boards, the boards' TS and WA was reduced by up to 64.2% and 78.8%, respectively.

Incorporating insulation material with phase change materials (PCMs) could help enhance the insulation capability for further building energy savings by reducing the HVAC loadings. During the phase change process between the solid and liquid states, heat is being absorbed or released by PCMs depending on the surrounding temperature. This research explores the benefits of a polyurethane (PU)-PCM composite insulation material through infiltrating paraffin wax as PCM into PU open cell foam. The new PU-PCM composite provides extra shielding from the exterior hot temperatures for buildings. Through this study, it was demonstrated that PU-PCM composite insulation could potentially help building energy savings through reducing the loads on the HVAC systems based on the building energy modeling using EnergyPlus. The Zero Energy Lab (ZØE) at the University of North Texas was modeled and studied in the EnergyPlus. It is a detached building with all wall facades exposed to the ambient. It was determined that the new PU-PCM insulation material could provide 14% total energy saving per year and reduce the electricity use due to cooling only by around 30%.

The goal of this dissertation is to demonstrate that data from a remotely located building can be utilized for energy modeling of a similar type of building and to demonstrate how to use this remote data without physically moving the data from one server to another using Virtual Information Fabric Infrastructure (VIFI). In order to achieve this goal, firstly an EnergyPlus model was created for Greek Life Center, a campus building located at University of North Texas campus at Denton in Texas, USA. Three thermal comfort models of Fanger model, Pierce two-node model and KSU two-node model were compared in order to find which one of these three models is most accurate to predict occupant thermal comfort. This study shows that Fanger's model is most accurate in predicting thermal comfort. Secondly, an experimental data pertaining to lighting usage and occupancy in a single-occupancy office from Carnegie Mellon University (CMU) has been implemented in order to perform energy analysis of Greek Life Center assuming that occupants in this building's offices behave similarly as occupants in CMU. Thirdly, different data types, data formats and data sources were identified which are required in order to develop a city-scale urban building energy model (CS-UBEM). …

This research work is focused on a conceptual combination of membrane-based energy recovery ventilator (ERV) and phase change material (PCM) to provide energy savings in building heating, ventilation & air-conditioning (HVAC) systems. An ERV can recover thermal energy and moisture between the outside fresh air (OFA) entering into the building and the exhaust air (EA) leaving from the building thus reducing the energy consumption of the HVAC system for cooling and heating the spaces inside the building. The membranes were stacked parallel to each other forming adjacent channels in a counter-flow arrangement for OFA and EA streams. Heat and moisture is diffused through the membrane core. Flat-plate encapsulated PCM is arranged in OFA duct upstream/downstream of the ERV thereby allowing for further reduction in temperature by virtue of free cooling. Paraffin-based PCMs with a melting point of 24°C and 31°C is used in two different configurations where the PCM is added either before or after the ERV. Computational fluid dynamics (CFD), and heat and mass transfer modeling is employed using COMSOL Multiphysics v5.3 to perform the heat and mass transfer analysis for the membrane-based ERV and flat-plate PCMs. An 8-story office building was considered to perform building energy simulation using …

In this study, the thermal properties of low dimensional materials such as graphene and boron nitride nanotube were investigated. As one of important heat transfer characteristics, interfacial thermal resistance (ITR) between graphene and Cu film was estimated by both experiment and simulation. In order to characterize ITR, the micropipette sensing technique was utilized to measure the temperature profile of suspended and supported graphene on Cu substrate that is subjected to continuous wave laser as a point source heating. By measuring the temperature of suspended graphene, the intrinsic thermal conductivity of suspended graphene was measured and it was used for estimating interfacial thermal resistance between graphene and Cu film. For simulation, a finite element method and a multiparameter fitting technique were employed to find the best fitting parameters. A temperature profile on a supported graphene on Cu was extracted by a finite element method using COMSOL Multiphysics. Then, a multiparameter fitting method using MATLAB software was used to find the best fitting parameters and ITR by comparing experimentally measured temperature profile with simulation one. In order to understand thermal transport between graphene and Cu substrate with different interface distances, the phonon density of states at the interface between graphene and Cu …

The goal of this research is to measure viscosity via the analysis of amplitude response of a piezo driven vibrating cantilevers partially immersed in a viscous medium. As a driving frequency is applied to a piezoceramic material, the external forces acting on the system will affect its maximum amplitude. This thesis applies this principle through experimental and analytical analyses of the proportional relationship between viscosity and the amplitude response of the first natural frequency mode of the sinusoidal vibration. Currently, the few cantilever-based viscometer designs that exist employ resonant frequency response as the parameter by which the viscosity is correlated. The proposed piezoelectric viscometer employs amplitude response in lieu of resonant frequency response. The goal of this aspect of the research was to provide data confirming amplitude response as a viable method for determining viscosity. A miniature piezoelectric plate was mounted to a small stainless-steel cantilever beam. The tip of the cantilever was immersed within various fluid test samples. The cantilever was then swept through a range of frequencies in which the first frequency mode resided. The operating principle being as the viscosity of the fluid increases the amplitude response of cantilever vibration will decrease relatively. What was found was …

This research investigates the bio-products/phase change material (PCM) composites for the building envelope application. Bio-products, such as wood and herb, are porous medium, which can be applied in the building envelope for thermal insulation purpose. PCM is infiltrated into the bio-product (porous medium) to form a composite material. The PCM can absorb/release large amount of latent heat of fusion from/to the building environment during the melting/solidification process. Hence, the PCM-based composite material in the building envelope can efficiently adjust the building interior temperature by utilizing the phase change process, which improves the thermal insulation, and therefore, reduces the load on the HVAC system. Paraffin wax was considered as the PCM in the current studies. The building energy savings were investigated by comparing the composite building envelope material with the conventional material in a unique Zero-Energy (ZØE) Research Lab building at University of North Texas (UNT) through building energy simulation programs (i.e., eQUEST and EnergyPlus). The exact climatic conditions of the local area (Denton, Texas) were used as the input values in the simulations. It was found that the EnergyPlus building simulation program was more suitable for the PCM based building envelope using the latent heat property. Therefore, based on the …

In this research, an elastic cylinder that utilized vortex-induced vibration (VIV) was applied to improve convective heat transfer rates by disrupting the thermal boundary layer. Rigid and elastic cylinders were placed across a fluid channel. Vortex shedding around the cylinder led to the periodic vibration of the cylinder. As a result, the flow-structure interaction (FSI) increased the disruption of the thermal boundary layer, and therefore, improved the mixing process at the boundary. This study aims to improve convective heat transfer rate by increasing the perturbation in the fluid flow. A three-dimensional numerical model was constructed to simulate the effects of different flow channel geometries, including a channel with a stationary rigid cylinder, a channel with a elastic cylinder, a channel with two elastic cylinders of the same diameter, and a channel with two elastic cylinders of different diameters. Through the numerical simulations, the channel maximum wall temperature was found to be reduced by approximately 10% with a stationary cylinder and by around 17% when introducing an elastic cylinder in the channel compared with the channel without the cylinder. Channels with two-cylinder conditions were also studied in the current research. The additional cylinder with the same diameter in the fluid channel …

Functionally graded materials (FGMs) are inhomogeneous materials in which the material properties vary with respect to space. Research has been done by scientific community in developing techniques like photothermal radiometry (PTR) to measure the thermal conductivity and volumetric heat capacity of FGMs. One of the problems involved in the technique is to solve the inverse problem, i.e., estimating the thermal properties after the frequency scan has been obtained. The present work involves finding the unknown thermal conductivity and volumetric heat capacity of the FGMs by using finite volume method. By taking the flux entering the sample as periodic and solving the discretized 1-D thermal wave field equation at a frequency domain, one can obtain the complex temperatures at the surface of the sample for each frequency. These complex temperatures when solved for a range of frequencies gives the phase vs frequency scan which can then be compared to original frequency scan obtained from the PTR experiment by using a residual function. Brute force and gradient descent optimization methods have been implemented to estimate the unknown thermal conductivity and volumetric specific heat of the FGMs through minimization of the residual function. In general, the spatial composition profile of the FGMs can …

Natural fibers like kenaf, hemp, flax and sisal fiber are becoming alternatives to conventional petroleum fibers for many applications. One such applications is the use of Non-woven bio-fiber mats in the automobile and construction industries. Non-woven hemp fiber mats were used to manufacture plywood in order to optimize the plywood structure. Hemp fiber mats possess strong mechanical properties that comparable to synthetic fibers which include tensile strength and tensile modulus. This study focuses on the use of hemp fiber mat as a core layer in plywood sandwich composite. The optimization of fiber mat plywood was done by performing a three factor experiment. The three factors selected for this experiment were number of hemp mat layers in the core, mat treatment of the hemp mat, and the glue content in the core. From the analysis of all treatments it was determined that single hemp mat had the highest effect on improving the properties of the plywood structure.

Fiber-metal laminates (FML) are the advanced materials that are developed to improve the high performance of lightweight structures that are rapidly becoming a superior substitute for metal structures. The reasons behind their emerging usage are the mechanical properties without a compromise in weight other than the traditional metals. The bond remains a concern. This thesis reviews the effect of pre-treatments, say heat, P2 etch and laser treatments on the substrate which modifies the surface composition/roughness to impact the bond strength. The constituents that make up the FMLs in our present study are the Aluminum 2024 alloy as the substrate and the carbon fiber prepregs are the fibers. These composite samples are manufactured in a compression molding process after each pre-treatment and are then subjected to different tests to investigate its properties in tension, compression, flexural and lap shear strength. The results indicate that heat treatment adversely affects properties of the metal and the joint while laser treatments provide the best bond and joint strength.

High entropy alloys (HEAs) are alloys with five or more principal elements. Due to these distinct concept of alloying, the HEA exhibits unique and superior properties. The outstanding properties of HEA includes higher strength/hardness, superior wear resistance, high temperature stability, higher fatigue life, good corrosion and oxidation resistance. Such characteristics of HEA has been significant interest leading to researches on these emerging field. Even though many works are done to understand the characteristic of these HEAs, very few works are made on how the HEAs can be applied for commercial uses. This work discusses the application of High entropy alloys in biomedical applications. The coronary heart disease, the leading cause of death in the United States kills more than 350,000 persons/year and it costs $108.9 billion for the nation each year in spite of significant advancements in medical care and public awareness. A cardiovascular disease affects heart or blood vessels (arteries, veins and capillaries) or both by blocking the blood flow. As a surgical interventions, stent implants are deployed to cure or ameliorate the disease. However, the high failure rate of stents has lead researchers to give special attention towards analyzing stent structure, materials and characteristics. Many works related to …

Knee osteoarthritis (KOA) is the primary cause of chronic immobility in populations over the age of 65. It is a joint degenerative disease in which the articular cartilage in the knee joint wears down over time, leading to symptoms of pain, instability, joint stiffness, and misalignment of the lower extremities. Without intervention, these symptoms gradually worsen over time, decreasing the overall knee range of motion (ROM) and ability to walk. Current clinical interventions include offloading braces, which mechanically realign the lower extremities to alleviate the pain experienced in the medial compartment of the knee joint. Though these braces have proven effective in pain management, studies have shown a significant decrease in knee ROM while using the brace. Concurrently, development of active exoskeletons for rehabilitative gait has increased within recent years in efforts to provide patients with a more effective intervention for dealing with KOA. Though some developed exoskeletons are promising in their efficacy of fostering gait therapy, these devices are heavy, tethered, difficult to control, unavailable to patients, or costly due to the number of complicated components used to manufacture the device. However, the idea that an active component can improve gait therapy for patients motivates this study. This study …

Corrosion represents the single most frequent cause for product replacement or loss of product functionality with a 5% coat to the industrial revenue generation of any country in this dissertation the efficacy of using filled coatings as a protection coating are investigated. Fillers disrupt the polymer-substrate coating interfacial area and lead to poor adhesion. Conflicting benefits of increasing surface hardness and corrosion with long term durability through loss of adhesion to the substrate are investigated. The effects of filler type, filler concentration and exposure to harsh environments such as supercritical carbon dioxide on salt water corrosion are systematically investigated. The constants maintained in the design of experiments were the substrate, AISI-SAE 1018 steel substrate, and the corrosive fluid synthetic sea salt solution (4.2 wt%) and the polymer, Bismaleimide (BMI). Adhesion strength through pull-off, lap shear and shear peel tests were determined. Corrosion using Tafel plots and electrochemical impedance spectroscopy was conducted. Vickers hardness was used to determine mechanical strength of the coatings. SEM and optical microscopy were used to examine dispersion and coating integrity. A comparison of fillers such as alumina, silica, hexagonal boron nitride, and organophilic montmorillonite clay (OMMT) at different concentrations revealed OMMT to be most effective with …

This work investigated a novel vapor chamber for efficient heat spreading and heat removal. A vapor chamber acting as a heat spreader enables for more uniform temperature distribution along the surface of the device being cooled. First, a vapor chamber was studied and compared with the traditional copper heat spreader. The thickness of vapor chamber was kept 1.35 mm which was considered to be ultra-thin vapor chamber. Then, a new geometrical model having graphite foam in vapor space was proposed where the graphite foam material was incorporated in vapor space as square cubes. The effects of incorporating graphite foam in vapor space were compared to the vapor chamber without the embedded graphite foam to investigate the heat transfer performance improvements of vapor chamber by the high thermal conductivity graphite foam. Finally, the effects of various vapor chamber thicknesses were studied through numerical simulations. It was found that thinner vapor chamber (1.35 mm thickness) had better heat transfer performance than thicker vapor chamber (5 mm thickness) because of the extreme high effective thermal conductivities of ultra-thin vapor chamber. Furthermore, the effect of graphite foam on thermal performance improvement was very minor for ultra-thin vapor chamber, but significant for thick vapor chamber. …

Energy efficiency in the operation of buildings is becoming increasingly important with a growing emphasis on sustainability and reducing environmental impacts of irresponsible energy usage. Improvements have been made both on the technology side of energy efficiency and on the human behavior side. However, when changing human behavior, it is critical to find energy conservation measures that will maintain comfort for occupants. This paper analyzes how this can be done by implementing a modulating temperature schedule based on the concept of alliesthesia, which states that pleasure is observed in transient states. EnergyPlus simulations were used to show that in cooling applications, this type of scheduling can produce significant energy savings. However, energy savings are not predicted for the same type of scheduling for heating applications. Thermal comfort was examined with a cooling experiment and a separate heating experiment, each lasting 45 minutes and taking place during the corresponding season. The experiments showed that modulating temperatures can cause occupants to experience more pleasure than if the temperature remained constant in a cooled space, whereas modulating temperatures had a negative impact on comfort relative to the constant temperature in the heated space. This presents evidence for an ideal opportunity for cooling applications …

Natural disasters are affecting a significant number of people around the world. Sheltering is the first step in post-disaster activities towards the normalization of the affected people's lives. Temporary housing is being used in these cases until the construction of permanent houses are done. Disposal of temporary housing after use is leading to a significant environmental impact because most of them are filled with thermally insulative polymer foams that do not degrade in a short period. To reduce these problems this work proposes to use foams made with compostable thermoplastic polylactic acid (PLA) and degradable kenaf core as filler materials; these foams are made using CO2 as blowing agent for insulation purposes. Foams with PLA and 5%, 10% and 15% kenaf core were tested. Different properties and their relations were examined using differential scanning calorimetry (DSC), thermal conductivity, mechanical properties, scanning electron microscopy (SEM), x-ray μ-computed tomography (μ-CT) and building energy simulations were done using Energy Plus by NREL. The results show that mechanical properties are reduced with the introduction of kenaf core reinforcement while thermal conductivity display a noticeable improvement.

Joining two dissimilar metals, specifically Mg and Al alloys, using conventional welding techniques is extraordinarily challenging. Even when these alloys are able to be joined, the weld is littered with defects such as cracks, cavities, and wormholes. The focus of this project was to use friction stir welding to create a defect-free joint between Al 2139 and Mg WE43. The stir tool used in this project, made of H13 tool steel, is of fixed design. The design included an 11 mm scrolled and concave shoulder in addition to a 6 mm length pin comprised of two tapering, threaded re-entrant flutes that promoted and amplified material flow. Upon completion of this project an improved experimental setup process was created as well as successful welds between the two alloys. These successful joints, albeit containing defects, lead to the conclusion that the tool used in project was ill fit to join the Al and Mg alloy plates. This was primarily due to its conical shaped pin instead of the more traditional cylindrical shaped pins. As a result of this aggressive pin design, there was a lack of heat generation towards the bottom of the pin even at higher (800-1000 rpm) rotation speeds. This …

This research demonstrates the use of friction stir welding (FSW) to join dissimilar (Al-Mg) metal alloys. The main challenges in joining different, dissimilar metal alloys is the formation of brittle intermetallic compounds (IMCs) in the stir zone affecting mechanical properties of joint significantly. In this present study, FSW joining process is used to join aluminum alloy AA2139 and magnesium alloy WE43. The 9.5 mm thick plates of AA2139 and WE43 were friction stir butt welded. Different processing parameters were used to optimize processing parameters. Also, various weldings showed a crack at interface due to formation of IMCs caused by liquation during FSW. A good strength sound weld was obtained using processing parameter of 1200 rev/min rotational speed; 76.2 mm/min traverse speed; 1.5 degree tilt and 0.13 mm offsets towards aluminum. The crack faded away as the tool was offset towards advancing side aluminum. Mostly, the research was focused on developing high strength joint through microstructural control to reduce IMCs thickness in Al-Mg dissimilar weld joint with optimized processing parameter and appropriate tool offset.

One of the major goal of the researchers is to reduce energy loss including nanoscale to the structural level. For instance, around 65% of fuel energy is lost during the propulsion of the automobiles, where 11% of the loss happens at tires due to rolling friction. Out of that tire loss, 90 to 95% loss happens due to hysteresis of tire materials. This dissertation focuses on multiscale modeling techniques in order to facilitate the discovery new rubber materials. Enhanced coarse-grained models of elastomers (thermoplastic polyurethane elastomer and natural rubber) are constructed from full-atomic models with reasonable repeat units/beads associated with pressure-correction for non-bonded interactions of the beads using inverse Boltzmann method (IBM). Equivalent continuum modeling is performed with volumetric/isochoric loading to predict macroscopic mechanical properties using molecular mechanics (MM) and molecular dynamics (MD). Glass-transition and rate-dependent mechanical properties along with hysteresis loss under uniaxial deformation is predicted with varying composition of the material. A statistical non-Gaussian treatment of a rubber chain is performed and linked with molecular dynamics in order predict hyperelastic material constants without fitting with any experimental data.

Magnesium alloys are a popular research topic for structural applications because they have a lower density than conventional structural materials, including steel, titanium, and aluminum; however, the reliability and safety of their mechanical properties must be further proven. An important mechanical property for this purpose is fracture toughness, which is the measure of the material's resistance to crack propagation. In this study, a model of an experiment to investigate the fracture toughness of a magnesium alloy WE43 before and after friction stir processing (FSP) is developed, and the results are compared to those produced by a digital image correlation (DIC) system during an experiment from another paper. The model results of the material before FSP matched well with the DIC results, but the model of the material after FSP only partially matches the DIC results. In addition, a theoretical approach to calculating the standard fracture toughness value, KIc, from the modeling results is proposed, and is found to be a conservative approach.