Field Validation of Zero Energy Lab Water-to-Water Ground Coupled Heat Pump Model (open access)

Field Validation of Zero Energy Lab Water-to-Water Ground Coupled Heat Pump Model

Heat pumps are a vital part of each building for their role in keeping the space conditioned for the occupant. This study focuses on developing a model for the ground-source heat pump at the Zero Energy lab at the University of North Texas, and finding the minimum data required for generating the model. The literature includes many models with different approaches to determine the performance of the heat pump. Each method has its pros and cons. In this research the equation-fit method was used to generate a model based on the data collected from the field. Two experiments were conducted for the cooling mode: the first one at the beginning of the season and the second one at the peak of the season to cover all the operation conditions. The same procedure was followed for the heating mode. The models generated based on the collected data were validated against the experiment data. The error of the models was within ±10%. The study showed that the error could be reduced by 20% to 42% when using the field data to generate the model instead of the manufacturer’s catalog data. Also it was found that the minimum period to generate the cooling …
Date: May 2016
Creator: Abdulameer, Saif
System: The UNT Digital Library
Source Apportionment Analysis of Measured Volatile Organic Compounds in Corpus Christi, Texas (open access)

Source Apportionment Analysis of Measured Volatile Organic Compounds in Corpus Christi, Texas

Corpus Christi among of the largest industrialized coastal urban areas in Texas. The strategic location of the city along the Gulf of Mexico allows for many important industries and an international business to be located. The cluster of industries and businesses in the region contribute to the air pollution from emissions that are harmful to the environment and to the people living in and visiting the area. Volatile organic compounds (VOC) constitute an important class of pollutants measured in the area. The automated gas chromatography (Auto GC) data was collected from Texas Commission of Environmental Quality (TCEQ) and source apportionment analysis was conducted on this data to identify key sources of VOC affecting this study region. EPA PMF 3.0 was employed in this sources apportionment study of measured VOC concentration during 2005 - 2012 in Corpus Christi, Texas. The study identified nine optimal factors (Source) that could explain the concentration of VOC at two urbane monitoring sites in the study region. Natural gas was found to be the largest contributor of VOC in the area, followed by gasoline and vehicular exhaust. Diesel was the third highest contributor with emissions from manufacturing and combustion processes. Refineries gases and evaporative fugitive emissions …
Date: May 2014
Creator: Abood, Ahmed T.
System: The UNT Digital Library
Development of a Cost Effective Wireless Sensor System for Indoor Air Quality Monitoring Applications (open access)

Development of a Cost Effective Wireless Sensor System for Indoor Air Quality Monitoring Applications

Poor air quality can greatly affect the public health. Research studies indicate that indoor air can be more polluted than the outdoor air. An indoor air quality monitoring system will help to create an awareness of the quality of air inside which will eventually help in improving it. The objective of this research is to develop a low cost wireless sensor system for indoor air quality monitoring. The major cost reduction of the system is achieved by using low priced sensors. Interface circuits had to be designed to make these sensors more accurate. The system is capable of measuring carbon dioxide, carbon monoxide, ozone, temperature, humidity and volatile organic compounds. The prototype sensor node modules were developed. The sensor nodes were the connected together by Zigbee network. The nodes were developed in such a way that it is compact in size and wireless connection of sensor nodes enable to collect air quality data from multiple locations simultaneously. The collected data was stored in a computer. We employed linear least-square approach for the calibration of each sensor to derive a conversion formula for converting the sensor readings to engineering units. The system was tested with different pollutants and data collected was …
Date: May 2014
Creator: Abraham, Sherin
System: The UNT Digital Library
Ultrafast Laser Sampling of a Plant Tissue and ion Conductivity Measurement for Investigation of Light Stress Generation Mechanisms (open access)

Ultrafast Laser Sampling of a Plant Tissue and ion Conductivity Measurement for Investigation of Light Stress Generation Mechanisms

In this study we applied ultra-short laser pulses on a biological sample (Arabidopsis), in order to cut it precisely in a square pattern and subsequently use it for studying stress generation mechanisms. For this purpose, we utilized femtosecond laser pulses at 100 fs pulse width and 80 MHz repetition rate. We took two processing parameters into consideration such as laser power, laser exposure time which is related to the stage speed. Therefore, we were able to find the laser optimum conditions for ablation of biological tissues. The mutant and wildtype (control) obtained from laser cutting with a size of 500 µm × 500 µm were directly transferred (in-situ with laser cutting) into a microfabricated chamber containing ~500 nanoliters deionized water for measuring ion conductivity. The ion conductivity is a signature of cell-death mechanisms caused by various stresses. A light with intensity of 100 µmol was exposed to the samples for 2 hours and 20 minutes as a source of stress. A quantitative electrical analysis with high accuracy was assured by utilizing a microchamber, which enables a measurement in nanoliter volume. We measured the impedance which is reciprocal of conductivity using a lock-in amplifier and a precise current source at frequency …
Date: August 2010
Creator: Abtahi, Seyed Ali
System: The UNT Digital Library
Gradient-Index Metamaterial Infrared Detector for Enhanced Photo-Response and Image Quality (open access)

Gradient-Index Metamaterial Infrared Detector for Enhanced Photo-Response and Image Quality

An enhanced thermal imaging concept made possible through the development of a gradient-indexed metamaterial infrared detector that offers broadband transmission and reflection in THz waves. This thesis proposes a proof of feasibility for a metamaterial infrared detector containing an anti-reflective coating with various geometrically varying periodic metasurfaces, a gradient-indexed dielectric multilayer for near-perfect longpass filtering, and a gradient index of refraction (GRIN) metalens for enhanced focal plane thermal imaging. 2D Rigorous Coupled-Wave Analysis (RCWA) is used for understanding the photonic gratings performance based on material selection and varying geometric structure. Finite Difference Time Domain (FDTD) is used to characterize performance for a diffractive metalens by optimizing the radius and arrangement of cylindrical nanorods to create a desired phase profile that can achieve a desired focal distance for projections on a detector for near- to far-infrared thermal imaging. Through combining a micromachined anti-reflective coating, a near-perfect longpass filter, and metamaterial GRIN metalens, infrared/THz focal plane thermal imaging can obtain faster photo-response and image quality at targeted wavelengths, which allows for scientific advancements in electro-optical devices for the Department of Defense, aerospace, and biochemical detection applications.
Date: May 2022
Creator: Adams, Kelsa Derek
System: The UNT Digital Library
Ozone Pollution of Shale Gas Activities in North Texas (open access)

Ozone Pollution of Shale Gas Activities in North Texas

The effect of shale gas activities on ground-level ozone pollution in the Dallas-Fort Worth area is studied in detail here. Ozone is a highly reactive species with harmful effects on human and environment. Shale gas development, or fracking, involves activities such as hydraulic fracturing, drilling, fluid mixing, and trucks idling that are sources of nitrogen oxides (NOX) and volatile organic compounds (VOC), two of the most important precursors of ozone. In this study two independent approaches have been applied in evaluating the influences on ozone concentrations. In the first approach, the influence of meteorology were removed from ozone time series through the application of Kolmogorov-Zurbenko low-pass filter, logarithmic transformation, and subsequent multi-linear regression. Ozone measurement data were acquired from Texas Commission on Environmental Quality (TCEQ) monitoring stations for 14 years. The comparison between ozone trends in non-shale gas region and shale gas region shows increasing ozone trends at the monitoring stations in close proximity to the Barnett Shale activities. In the second approach, the CAMx photochemical model was used to assess the sensitivity of ozone to the NOX and VOC sources associated with shale oil and gas activities. Brute force method was applied on Barnett Shale and Haynesville Shale emission …
Date: May 2016
Creator: Ahmadi, Mahdi
System: The UNT Digital Library
Effectiveness of Fillers for Corrosion Protection of AISI-SAE 1018 Steel in Sea Salt Solution (open access)

Effectiveness of Fillers for Corrosion Protection of AISI-SAE 1018 Steel in Sea Salt Solution

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 …
Date: May 2017
Creator: Al-Shenawa, Amaal
System: The UNT Digital Library
Application of High Entropy Alloys in Stent Implants (open access)

Application of High Entropy Alloys in Stent Implants

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 …
Date: May 2017
Creator: Alagarsamy, Karthik
System: The UNT Digital Library
Thermal Transport Modeling in Three-Dimensional Pillared-Graphene Structures for Efficient Heat Removal (open access)

Thermal Transport Modeling in Three-Dimensional Pillared-Graphene Structures for Efficient Heat Removal

Pillared-graphene structure (PGS) is a novel three-dimensional structure consists of parallel graphene sheets that are separated by carbon nanotube (CNT) pillars that is proposed for efficient thermal management of electronics. For microscale simulations, finite element analyses were carried out by imposing a heat flux on several PGS configurations using a Gaussian pulse. The temperature gradient and distribution in the structures was evaluated to determine the optimum design for heat transfer. The microscale simulations also included conducting a mesh-independent study to determine the optimal mesh element size and shape. For nanoscale simulations, Scienomics MAPS software (Materials And Processes Simulator) along with LAMMPS (Large-scale Atomic/ Molecular Massively Parallel Simulator) were used to calculate the thermal conductivity of different configurations and sizes of PGS. The first part of this research included investigating PGS when purely made of carbon atoms using non-equilibrium molecular dynamics (NEMD). The second part included investigating the structure when supported by a copper foil (or substrate); mimicking production of PGS on copper. The micro- and nano-scale simulations show that PGS has a great potential to manage heat in micro and nanoelectronics. The fact that PGS is highly tunable makes it a great candidate for thermal management applications. The simulations were …
Date: December 2020
Creator: Almahmoud, Khaled Hasan Musa
System: The UNT Digital Library
Design Optimization of Functionalized Silica-Polymer Nanocomposite through Finite Element and Molecular Dynamics Modeling (open access)

Design Optimization of Functionalized Silica-Polymer Nanocomposite through Finite Element and Molecular Dynamics Modeling

This dissertation focuses on studying membrane air dehumidification for a membrane moisture exchanger in a membrane heat pump system. The study has two parts: an optimization of membrane moisture exchanger for air dehumidification in the macroscale, and diffusion of water vapor in polymer nanocomposites membrane for humid air dehumidification in the nanoscale. In the first part of the research, the mass transport of water vapor molecules through hydrophilic silica nanochannel chains in hydrophobic polyurethane matrix was studied by simulations and experiments for different membrane moisture exchanger design configurations. The mass transport across the polymer nanocomposite membrane occurs with the diffusion of moist air water vapor molecules in the membrane moisture exchanger in a membrane heat pump air conditioning system for air dehumidification purposes. The hydrophobic polyurethane matrix containing the hydrophilic silica nanochannel chains membrane is responsible for transporting water vapor molecules from the feed side to the permeate side of the membrane without allowing air molecules to pass through.In the second part of the research, diffusion analysis of the polymer nanocomposite membrane were performed in the nanoscale for the polymer nanocomposite membrane. The diffusion phenomena through the polymer, the polymer nanocomposite without modifying the silica surfaces, and the polymer nanocomposite …
Date: August 2020
Creator: Almahmoud, Omar H. M.
System: The UNT Digital Library

Design, Fabrication and Testing of a Novel Dual-Axis Automatic Solar Tracker System Using a Fresnel-Lens Solar Concentrator

This thesis project investigates, analyzes, designs, simulates, constructs and tests a dual-axis solar tracker system to track the sun and concentrates the heat of the sunlight, using a Fresnel lens, into a small area, which is above of an evaporator, to increase the temperature of the seawater to convert it into freshwater. The dual-axis solar tracker was designed with the main objectives that the structure was portable, dismountable, lightweight, low cost, corrosion resistant, wires inside pipes, accurate, small size, follow the sun automatically, off-grid (electrical), use green energy (solar powered), and has an empty area right below of the lens. First, a 500 mm diameter flat Fresnel lens was selected and simulated based on an algorithmic method achieved by a previous PhD student at UNT using MATLAB®, to give the optimization lens dimensions. The lens profile was drawn with AutoCAD®, then output profile lens was simulated in COMSOL Multiphysics®. The objective was to provide the high efficiency, optimum and high precision of the focal rays and heat to the receiver of the evaporator. A novel dual-axis solar tracker system was then designed that is portable, dismountable, lightweight and corrosion resistant. The solar tracker tracks the sun in two axis of …
Date: August 2021
Creator: Almara, Laura Mabel
System: The UNT Digital Library

3D Printing of Zinc Anode for Zinc Ion Batteries

Recently, 3D printing has received increasing attention for the fabrication and assembly of electrodes for batteries due to the freedom of creating structures in any shape or size, porosity, flexibility, stretchability, and chemistry. Particularly, zinc ion batteries (ZIBs) are favored due to high safety, cheap materials cost, and high volumetric capacity (5,849 mAh/cm3), however, rapid evaporation of Zn due to low melting temperature has limited its 3D printability via conventional laser-based additive manufacturing technique. Here, we develop a printable ink for the fabrication of flexible and 3D printed Zn anode with varied surface areas using the direct ink writing (DIW) method. Our 3D printed porous and high surface area Zn anode structures effectively suppressed the dendrite growth while providing high Zn ion diffusion towards the cathode to significantly enhance the performance of ZIB. By varying filament distancing and path, we 3D printed zinc anode structures with different active surface areas, surface area to volume ratio, porosity, flexible and multiple layer structures that can be incorporated on any device. Carbon in the composite improved conductivity, and mechanical stability of 3D printed zinc anode. Our 3D printed composite anodes allowed flexible designing of batteries surpassing conventional battery designs such as coin cells …
Date: December 2021
Creator: Amoko, Stephen Adot Oyo
System: The UNT Digital Library
Development of a Natural Fiber Mat Plywood Composite (open access)

Development of a Natural Fiber Mat Plywood Composite

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.
Date: August 2017
Creator: Anthireddy, Prasanna Kumar
System: The UNT Digital Library
Optical Transparent Pmma Composite Reinforced By Coaxial Electrospun Pan Hollow Nanofibers (open access)

Optical Transparent Pmma Composite Reinforced By Coaxial Electrospun Pan Hollow Nanofibers

Electrospinning has been recognized as an efficient technique for the fabrication of polymer fibers. These electrospun fibers have many applications across a broad range of industries. In this research, optical transparent composites were successfully fabricated by embedding polyacrylonitrile (PAN) hollow nanofibers into poly (methyl methacrylate) (PMMA) matrix. The hollow PAN nanofibers were prepared by coaxial electrospinning. The PAN was used as the shell solution, and the mineral oil was used as the core solution. The resulting fibers were then etched with octane to remove the mineral oil from the core. The hollow PAN fibers were then homogeneously distributed in PMMA resins to fabricate the composite. The morphology, transmittance and mechanical properties of the PAN/PMMA composite were then characterized with an ESEM, TEM, tensile testing machine, UV-vis spectrometer and KD2 Pro Decagon device. The results indicated that the hollow nanofibers have relatively uniform size with one-dimensional texture at the walls. The embedded PAN hollow nanofibers significantly enhanced the tensile stress and the Young's modulus of the composite (increased by 58.3% and 50.4%, respectively), while having little influence on the light transmittance of the composite. The KD2 Pro device indicated that the thermal conductivity of the PMMA was marginally greater than the …
Date: May 2013
Creator: Antoine, Donley
System: The UNT Digital Library
Optimization of Silica Nanocomposite Membranes for Air Dehumidification (open access)

Optimization of Silica Nanocomposite Membranes for Air Dehumidification

This thesis is focused on understanding the correct method to simulate atomistic models to calculate coefficient of diffusion of water through the membrane. It also aims to fix the method previously used in molecular modelling in which the simulation results did not match the experimental results. These membranes will be used in air dehumidification systems. The four types of membranes namely, polyurethane, polyurethane with silica nano particles, polyurethane with silica nano particles and amine surface modifier, and polyurethane with silica nano particles and aniline surface modifier. These membranes were also simulated to understand the effects of temperatures and pressure using molecular dynamics. The software packages used are MAPS 4.3, Avogadro, EMC, OVITO, and LAMMPS. MAPS, Avogadro and EMC were used to model the membrane at an atomistic level while LAMMPS is used to simulate the model generated. OVITO is used to analyze the simulation visually. The movement of water vapor molecules were tracked through the membrane in the simulation and diffusion coefficient was calculated using Mean square displacement equation. To create a realistic model, silica was dispersed in the Polyurethane matrix, simulated under standard atmospheric conditions. These results will help in further optimizing the membrane for air dehumidification. This will …
Date: May 2022
Creator: Appaji, Tejas
System: The UNT Digital Library
Tuning Effect on Thermal Radiative Emission of Thermo-Mechano-Optical Gratings and Multilayers (open access)

Tuning Effect on Thermal Radiative Emission of Thermo-Mechano-Optical Gratings and Multilayers

The recipes of optical radiative properties manipulation are their materials chemistry, nano/microscale geometry, and transport properties of quasiparticle carriers such as photons, phonons, and electrons. The important technical element in optical properties is the dielectric function of materials, which is different for metals, dielectrics, 2D materials, and phase transition materials. Graphene has a unique electrical conductivity profile which have metallic nature depending on the frequency, but also has a negative thermal expansion coefficient that makes graphene unique. Hence, graphene creates wrinkles when deposited on the substrate as temperature decreases to room temperature from high substrate temperature. We also study phase transition material, particularly vanadium dioxide that transitions from insulating to metallic phase based on temperature change; we investigate its role in far-field thermal radiation. Other transition metal oxides are studied as a thermally and electrically tunable plasmonic gratings: Transition metal oxides include vanadium dioxide, tungsten trioxide, and molybdenum trioxide. The work demonstrates plasmonic phenomena and absorptance/emittance tunability. First, surface plasmon polariton along the graphene (SPPG) when wrinkles are formed above the plasmonic grating is studied. The resonance peak shift is modeled for both magnetic polariton (MP) with inductor-capacitor (LC) circuit and SPPG with Fabry-Perot phase change model. Second, the self-adaptive …
Date: December 2022
Creator: Araki, Ken
System: The UNT Digital Library

Characterization, Analysis, and Optimization of Rotary Displacer Stirling Engines

Access: Use of this item is restricted to the UNT Community
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 …
Date: December 2019
Creator: Bagheri, Amirhossein
System: The UNT Digital Library
Effect of Surface Treatment on the Performance of CARALL, Carbon Fiber Reinforced Aluminum Dissimilar Material Joints (open access)

Effect of Surface Treatment on the Performance of CARALL, Carbon Fiber Reinforced Aluminum Dissimilar Material Joints

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.
Date: August 2017
Creator: Bandi, Raghava
System: The UNT Digital Library

Thermal Transport Properties Enhancement of Phase Change Material by Using Boron Nitride Nanomaterials for Efficient Thermal Management

In this research thermal properties enhancement of phase change material (PCM) using boron nitride nanomaterials such as nanoparticles and nanotubes is studied through experimental measurements, finite element method (FEM) through COMSOL 5.3 package and molecular dynamics simulations via equilibrium molecular dynamics simulation (EMD) with the Materials and Process Simulations (MAPS 4.3). This study includes two sections: thermal properties enhancement of inorganic salt hydrate (CaCl2∙6H2O) as the phase change material by mixing boron nitride nanoparticles (BNNPs), and thermal properties enhancement of organic phase change material (paraffin wax) as the phase change material via encapsulation into boron nitride nanotubes (BNNTs). The results of the proposed research will contribute to enhance the thermal transport properties of inorganic and organic phase change material applying nanotechnology for increasing energy efficiency of systems including electronic devices, vehicles in cold areas to overcome the cold start problem, thermal interface materials for efficient heat conduction and spacecraft in planetary missions for efficient thermal managements.
Date: December 2020
Creator: Barhemmati Rajab, Nastaran
System: The UNT Digital Library
Conceptual Framework for the Development of an Air Quality Monitoring Station in Denton, Texas (open access)

Conceptual Framework for the Development of an Air Quality Monitoring Station in Denton, Texas

Denton, Texas consistently reaches ozone nonattainment levels. This has led to a large focus of air pollution monitoring efforts in the region, with long-range transport being explored as a key contributor. For this study, the University of North Texas Discovery Park campus was chosen as a prospective location for an extensive air quality monitoring station. Sixteen years of ozone and meteorological data for five state-run monitoring sites within a 25 mile radius, including the nearest Denton Airport site, was gathered from TCEQ online database for the month of April for the years 2000 to 2015. The data was analyzed to show a historical, regional perspective of ozone near the proposed site. The maximum ozone concentration measured at the Denton Airport location over the 16 year period was measured at 96 ppb in 2001. Experimental ozone and meteorological measurements were collected at the Discovery Park location from March 26 to April 3 and April 8 to April, 2016 and compared to the Denton Airport monitoring site. A time lag in ozone trends and an increase in peak ozone concentrations at the proposed location were observed at the proposed site in comparison to the Denton Airport site. Historical and experimental meteorological data …
Date: August 2016
Creator: Boling, Robyn
System: The UNT Digital Library
Use of Bio-Product/Phase Change Material Composite in the Building Envelope for Building Thermal Control and Energy Savings (open access)

Use of Bio-Product/Phase Change Material Composite in the Building Envelope for Building Thermal Control and Energy Savings

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 …
Date: August 2018
Creator: Boozula, Aravind Reddy
System: The UNT Digital Library
Design of a Lower Extremity Exoskeleton to Increase Knee ROM during Valgus Bracing for Osteoarthritic Gait (open access)

Design of a Lower Extremity Exoskeleton to Increase Knee ROM during Valgus Bracing for Osteoarthritic Gait

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 …
Date: May 2017
Creator: Cao, Jennifer M.
System: The UNT Digital Library
Loading Mode Dependent Effective Properties of Octet-truss Lattice Structures Using 3D-Printing (open access)

Loading Mode Dependent Effective Properties of Octet-truss Lattice Structures Using 3D-Printing

Cellular materials, often called lattice materials, are increasingly receiving attention for their ultralight structures with high specific strength, excellent impact absorption, acoustic insulation, heat dissipation media and compact heat exchangers. In alignment with emerging additive manufacturing (AM) technology, realization of the structural applications of the lattice materials appears to be becoming faster. Considering the direction dependent material properties of the products with AM, by directionally dependent printing resolution, effective moduli of lattice structures appear to be directionally dependent. In this paper, a constitutive model of a lattice structure, which is an octet-truss with a base material having an orthotropic material property considering AM is developed. In a case study, polyjet based 3D printing material having an orthotropic property with a 9% difference in the principal direction provides difference in the axial and shear moduli in the octet-truss by 2.3 and 4.6%. Experimental validation for the effective properties of a 3D printed octet-truss is done for uniaxial tension and compression test. The theoretical value based on the micro-buckling of truss member are used to estimate the failure strength. Modulus value appears a little overestimate compared with the experiment. Finite element (FE) simulations for uniaxial compression and tension of octet-truss lattice materials …
Date: May 2015
Creator: Challapalli, Adithya
System: The UNT Digital Library
Heat Transfer Analysis of Bio-Printed Tissue Mimicking Material Mixed with Silver Nanoparticles (open access)

Heat Transfer Analysis of Bio-Printed Tissue Mimicking Material Mixed with Silver Nanoparticles

Novel tissue mimicking materials have been developed for cancer treatment research. In the present research work, the tissue mimicking material is printed using 3D bioprinting technology. The nanoparticles are homogeneously mixed with tissue mimicking materials to enhance the heating capacity. The thermal conductivity of tissue mimicking materials is measured using a micropipette thermal sensor (MTS). Further, the optimal value is identified based on optimization technique and incorporated into a theoretical model to predict the surface temperature of microsphere. The heat conduction governing equation with Lambert law is numerically solved using COMSOL Multiphysics software. To validate the present simulation results, the experiments are conducted using a continuous laser system.
Date: August 2022
Creator: Chandrasegaran, Jedeshkeran
System: The UNT Digital Library