Semiconductor die attach materials for high voltage, high reliability analog devices require high thermal conductivity and retention of dielectric strength. A comparative study of effective thermal conductivity and dielectric strength of selected thermoset/ceramic composites was conducted to determine the effect of ceramic particle size and ceramic particle loading on thermoset polymers. The polymer chosen for this study is bismaleimide, a common aerospace material chosen for its strength and thermal stability. The reinforcing material chosen for this study is a ceramic, hexagonal boron nitride. Thermal conductivity and dielectric breakdown strength are measured in low and high concentrations of hexagonal boron nitride. Adhesive fracture toughness of the composite is evaluated on copper to determine the composite’s adhesive qualities. SEM imaging of composite cross-sections is used to visualize particle orientation within the matrix. Micro-indentation is used to measure mechanical properties of the composites which display increased mechanical performance in loading beyond the percolation threshold of the material. Thermal conductivity of the base polymer increases by a factor of 50 in 80%wt loading of 50µm hBN accompanied by a 10% increase in composite dielectric strength. A relationship between particle size and effective thermal conductivity is established through comparison of experimental data with an empirical …

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 …

Two-dimensional (2D) transition metal dichalcogenides (TMDs) show great potential for the future electronics, optoelectronics and energy applications. But, the studies unveiling their interactions with the host substrates are sparse and limits their practical use for real device applications. We report the facile nano-scratch method to determine the adhesion energy of the wafer scale MoS2 atomic layers attached to the SiO2/Si and sapphire substrates. The practical adhesion energy of monolayer MoS2 on the SiO2/Si substrate is 7.78 J/m2. The practical adhesion energy was found to be an increasing function of the MoS2 thickness. Unlike SiO2/Si substrates, MoS2 films grown on the sapphire possess higher bonding energy, which is attributed to the defect-free growth and less number of grain boundaries, as well as less stress and strain stored at the interface owing to the similarity of Thermal Expansion Coefficient (TEC) between MoS2 films and sapphire substrate. Furthermore, we calculated the surface free energy of 2D MoS2 by the facile contact angle measurements and Neumann model fitting. A surface free energy ~85.3 mJ/m2 in few layers thick MoS2 manifests the hydrophilic nature of 2D MoS2. The high surface energy of MoS2 helps explain the good bonding strength at MoS2/substrate interface. This simple adhesion …

Dynamic tensile characterization of geo-materials is critical to the modeling and design of protective structures that are often made of concrete. One of the most commonly used techniques currently associated with this type of testing is performed with a Kolsky bar and is known as the spall technique. The validity of the data from the spall technique is highly debated because the necessary boundary conditions for the experiment are not satisfied. By using a technique called pulse shaping, a new “controlled” spall technique was developed to satisfy all boundary conditions so that the analyzed data may be useful in modeling and design. The results from this project were promising and show the potential to revolutionize the way Kolsky bar testing is performed.

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 …

The following report chronicles the University of North Texas Wind Turbine Project at Apogee Stadium. The timeline of events will include the feasibility study conducted by and for the university, grant awards from the Texas State Energy Conservation Office to fund the project, and a three-year sample of real time performance data since installation. The purpose of this case study is to compare the energy generation estimates by various stakeholders to the measured energy generation using a new but uniform performance relationship. In order to optimize energy generation in wind turbine generator systems, the most common wind speeds measured at the site should also be the most efficient wind speeds at which the wind turbine can convert the kinetic energy in the wind into mechanical energy and ultimately electrical energy. The tool used to convey this relationship will be a figure plotting the wind speed profile against the efficiency curve of the wind turbine. Applying this relationship tool to the UNT Apogee Stadium wind turbines provided valuable results. The most common wind speeds at Apogee Stadium are not the most efficient wind speed for the turbine. Also, the most common wind speeds were near the lower limit of the wind …

There is a wide range of applications for 3D printing technology with an additive manufacturing such as aerospace, automotive, marine and oil/gas, medical, consumer, electronics, building construction, and many others. There have been many pros and cons for 3D additive manufacturing. Even though 3D printing technology has many advantages: freedom to design and innovate without penalties, rapid iteration through design permutations, excellence mass customization, elimination of tolling, green manufacturing, minimal material wastes, energy efficiency, an enablement of personalized manufacturing. 3D additive manufacturing still has many disadvantages: unexpected pre- and post-processing requirement, high-end manufacturing, low speed for mass production, high thermal residual stress, and poor surface finish and dimensional accuracy, and many others. Especially, the issues for 3D additive manufacturing are on high cost for process and equipment for high-end manufacturing, low speed for mass production, high thermal residual stress, and poor surface finish and dimensional accuracy. In particular, it is relatively challenging to produce casting products with lattice or honeycomb shapes having sophisticated geometries. In spite of the scalable potential of periodic cellular metals to structural applications, the manufacturing methods of I∙AM Casting have been not actively explored nor fully understood. A few qualitative studies of I∙AM Casting has been …

The addition of hexagonal boron nitride (h-BN) has introduced a comprehensive reinforcing effect to the mechanical and electrochemical properties of commercial concrete, including fiber reinforced concrete (FRC) and steel fiber reinforced concrete (SFRC). Although this has been proven effective and applicable, further investigation and study is still required to optimize the strengthen result which will involve the exfoliation of h-BN into single-layered nano sheet, improving the degree of dispersion and dispersion uniformity of h-BN into concrete matrix. There is currently no direct method to test the degree of dispersion of non-conductive particles, including h-BN, in concrete matrix, therefore it is necessary to obtain an analogous quantification method like SEM, etc. The reinforcing mechanism on concrete, including FRC and SFRC is now attracting a great number of interest thanks to the huge potential of application and vast demand across the world. This study briefly describes the reinforcing mechanism brought by h-BN. In this study, different samples under varied conditions were prepared according to the addition of h-BN and dispersant to build a parallel comparison. Characterization is mainly focused on their mechanical properties, corrosive performance and SEM analysis of the cross-section of post-failure samples.

Emissions of air pollutants from non-conventional sources have been on the rise in the North Texas area over the past decade. These include primary pollutants such as volatile organic compound (VOC) and oxides of nitrogen (NOx) which also act as precursors in the formation of ozone. Most of these have been attributed to a significant increase in oil and gas production activities since 2000 within the Barnett Shale region adjacent to the Dallas-Fort Worth metroplex region. In this study, air quality concentrations measured at the Denton Airport and Dallas Hinton monitoring sites operated by the Texas Commission on Environmental Quality (TCEQ) were evaluated. VOC concentration data from canister-based sampling along with continuous measurement of oxides of nitrogen (NOx), ozone (O3), particulate matter (PM2.5), and meteorological conditions at these two sites spanning from 2000 through 2014 were employed in this study. The Dallas site is located within the urban core of one of the fastest growing cities in the United States, while the Denton site is an exurban site with rural characteristics to it. The Denton Airport site was influenced by natural gas pads surrounding it while there are very few natural gas production facilities within close proximity to the Dallas …

For years, the alloy of choice for electroplating electronic components has been tin-lead (Sn-Pb) alloy. However, the legislation established in Europe on July 1, 2006, required significant lead (Pb) content reductions from electronic hardware due to its toxic nature. A popular alternative for coating electronic components is pure tin (Sn). However, pure tin has the tendency to spontaneously grow electrically conductive Sn whisker during storage. Sn whisker is usually a pure single crystal tin with filament or hair-like structures grown directly from the electroplated surfaces. Sn whisker is highly conductive, and can cause short circuits in electronic components, which is a very significant reliability problem. The damages caused by Sn whisker growth are reported in very critical applications such as aircraft, spacecraft, satellites, and military weapons systems. They are also naturally very strong and are believed to grow from compressive stresses developed in the Sn coating during deposition or over time. The new directive, even though environmentally friendly, has placed all lead-free electronic devices at risk because of whisker growth in pure tin. Additionally, interest has occurred about studying the nature of other metal whiskers such as zinc (Zn) whiskers and comparing their behavior to that of Sn whiskers. Zn …

While many investigations have been performed to establish a better understanding of the effects that magnetic fields and nanoparticles have on cells, the fundamental mechanisms behind the interactions are still yet unknown, and investigations on concurrent exposure are quite limited in scope. This study was therefore established to investigate the biological impact of concurrent exposure to magnetic nanoparticles and extremely-low frequency magnetic fields using an in-vitro CHO-K1 cell line model, in an easily reproducible manner to establish grounds for further in-depth mechanistic, proteomic, and genomic studies. Cells were cultured and exposed to 10nm Fe3O4 nanoparticles, and DC or low frequency (0Hz, 50Hz, and 100Hz) 2.0mT magnetic fields produced by a Helmholtz coil pair. The cells were then observed under confocal fluorescence microscopy, and subject to MTT biological assay to determine the synergistic effects of these concurrent exposures. No effects were observed on cell morphology or microtubule network; however, cell viability was observed to decrease more drastically under the combined effects of magnetic field and nanoparticle exposures, as compared to independent exposures alone. It was concluded that no significant difference was observed between the types of magnetic fields, and their effects on the nanoparticle exposed cells, but quite clearly there are …

The Barnett shale basin, the largest onshore gas field in the state of Texas, mainly produces natural gas. The basin’s oil and gas productions have dramatically increased over the past two decades with the enhancement via shale fracturing (fracking) technology. However, recent studies suggest that air emissions from shale fracking have significantly contributed to the growing air pollution problem in North Texas. In this study, air emissions from the Barnett shale basin during the production phase of the oil and gas activities (once the product is collected from the wells) are quantified. Oil and gas production data were acquired from the Texas Railroad Commission for the baseline years of 2010 through 2013. Methodology from prior studies on shale basins approved by the Texas Commission on Environmental Quality was employed in this study and the emission inventories from the production phase sources were quantified. Accordingly, the counties with the most gas operations in the basin, Tarrant, Johnson, Denton and Wise, were found to be the highest emitters of air pollutants. Tarrant County was responsible for the highest emitted NOx (42,566 tons) and CO (17,698 tons) in the basin, while Montague County released the maximum VOC emissions (87,601 tons) during the study …

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 …

Fiber-reinforced concrete (FRC) is nowadays extensively used in civil engineering throughout the world due to the composites of FRC can improve the toughness, flexural strength, tensile strength, and impact strength as well as the failure mode of the concrete. It is an easy crazed material compared to others materials in civil engineering. Concrete, like glass, is brittle, and hence has a low tensile strength and shear capacity. At present, there are different materials that have been employed to reinforce concrete. In our experiment, nanostructures iron oxide was prepared by electrodepostion in an electrolyte containing 0.2 mol/L sodium acetate (CH3COONa), 0.01 mol/L sodium sulfate (Na2SO4) and 0.01 mol/L ammonium ferrous sulfate (NH4)2Fe(SO4)2.6H2O under magnetic stirring. The resulted showed that pristine Fe2O3 particles, Fe2O3 nanorods and nanosheets were synthesized under current intensity of 1, 3, 5 mA, respectively. And the pull-out tests were performed by Autograph AGS-X Series. It is discovering that the load force potential of nanostructure fibers is almost 2 times as strong as the control sample.

A recent trend in the development of renewable and biodegradable materials has led to the development of composites from renewal sources such as natural fibers. This agricultural activity generates a large amount of waste in the form of peanut shells. The motivation for this research is based on the utilization of peanut shells as a viable source for the manufacture of biocomposites. High-density polyethylene (HDPE) is a plastic largely used in the industry due to its durability, high strength to density ratio, and thermal stability. This research focuses in the mechanical and thermal properties of HDPE/peanut shell composites of different qualities and compositions. The samples obtained were subjected to dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and mechanical tensile strength tests. TO prepare the samples for analysis, the peanut shells were separated into different mesh sizes and then mixed with HDPE at different concentrations. The results showed that samples with fiber size number 10 exhibited superior strength modulus of 1.65 GPa versus results for HDPE alone at 1.32 GPa. The analysis from the previous experiments helped to determine that the fiber size number 10 at 5%wt. ratio in HDPE provides the most optimal mechanical and thermal results. From tensile …

In this study the author reports the effects of surface roughness on dynamic behavior of water droplets on different types of rough structures. First, the influence of roughness geometry on the Wenzel/ Cassie-Baxter transition of water droplets on one-tier (solid substrates with Si micropillars) surfaces is studied (Chapter 3). In order to address distinct wetting behaviors of the advancing and receding motions, the author investigates the Wenzel/ Cassie-Baxter transition of water droplets on one-tier surfaces over a wide range of contact line velocities and droplet volumes in both advancing and receding movements. The discussions are strengthened by experimental results. According to the author’s analysis, the advancing contact zone tends to follow the Cassie-Baxter behavior for a wider range of geometric ratios than the receding contact zone. Physical phenomena such as advancing contact line rolling mechanism and the pinning of the receding contact line are introduced to justify distinct transition points of the advancing and receding movements respectively. Based on the analysis provided in Chapter 3, the author experimentally investigates the contact line fluctuations and contact line friction coefficients of water droplets on smooth, one-tier, and two-tier (with carbon nanotubes (CNTs) grown on Si micropillars) surfaces in Chapters 4 and 5. …

Microchannels have been used in electronics cooling and in air conditioning applications as condensers. Little study has been made in the application of microchannels in automotive heat exchangers, particularly the radiator. The presented research captures the need for the design improvement of radiator heat exchangers in heavy-duty vehicles in order to reduce aerodynamic drag and improve fuel economy. A method for analyzing an existing radiator is set forth including the needed parameters for effective comparisons of alternative designs. An investigation of microchannels was presented and it was determined that microchannels can improve the overall heat transfer of a radiator but this alone will not decrease the dimensions of the radiator. Investigations into improving the air-side heat transfer were considered and an improved fin design was found which allows a reduction in frontal area while maintaining heat transfer. The overall heat transfer of the design was improved from the original design by 7% well as 52% decrease in frontal area but at the cost of 300% increase in auxiliary power. The energy saved by a reduction in frontal area is not substantial enough to justify the increase of auxiliary power. The findings were verified through a computational fluid dynamic model to …

The electromagnetic shielding effectiveness of kenaf bast fiber based composites with different iron oxide impregnation levels was investigated. The kenaf fibers were retted to remove the lignin and extractives from the pores in fibers, and then magnetized. Using the unsaturated polyester and the magnetized fibers, kenaf fiber based composites were manufactured by compression molding process. The transmission energies of the composites were characterized when the composite samples were exposed under the irradiation of electromagnetic (EM) wave with a changing frequency from 9 GHz to 11 GHz. Using the scanning electron microscope (SEM), the iron oxide nanoparticles were observed on the surfaces and inside the micropore structures of single fibers. The SEM images revealed that the composite’s EM shielding effectiveness was increased due to the adhesion of the iron oxide crystals to the kenaf fiber surfaces. As the Fe content increased from 0% to 6.8%, 15.9% and 18.0%, the total surface free energy of kenaf fibers with magnetizing treat increased from 44.77 mJ/m2 to 46.07 mJ/m2, 48.78 mJ/m2 and 53.02 mJ/m2, respectively, while the modulus of elasticity (MOE) reduced from 2,875 MPa to 2,729 MPa, 2,487 MPa and 2,007 MPa, respectively. Meanwhile, the shielding effectiveness was increased from 30-50% to 60-70%, …

TSDC (thermally stimulated depolarization current) is one of the most important and popular technique for investigating electret materials. TSDC technique can indicate the magnitude of polarization and depolarization, relaxation time, charge-storage, glass transition, and activation energy. To fully investigate polarization and relaxation for pure epoxy and filled epoxy materials, a TSDC system was built and verified by the research. The article describes the building processes and verification of the TSDC system. TSDC, TSPC, and TWC tests data for epoxy and filled epoxy samples are presented in the article. To compare TSDC technique with other related techniques, DEA (dielectric analysis), DMA (dynamic mechanical analysis), and DSC (differential scanning calorimetry) tests are introduced.

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 …

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 …

The study focuses on the sensitivity and uncertainty analysis of occupancy-related parameters using Energyplus modeling method. The model is based on a real building Zero Energy Lab in Discovery Park, at University of North Texas. Four categories of parameters are analyzed: heating/cooling setpoint, lighting, equipment and occupancy. Influence coefficient (IC) is applied in the sensitivity study, in order to compare the impact of individual parameter on the overall building energy consumption. The study is conducted under Texas weather file as well as North Dakota weather file in order to find weather’s influence of sensitivity. Probabilistic collocation method (PCM) is utilized for uncertainty analysis, with an aim of predicting future energy consumption based on history or reference data set. From the study, it is found that cooling setpoint has the largest influence on overall energy consumption in both Texas and North Dakota, and occupancy number has the least influence. The analysis also indicates schedule’s influence on energy consumption. PCM is able to accurately predict future energy consumption with limited calculation, and has great advantage over Monte Carlo Method. The polynomial equations are generated in both 3-order and 6-order, and the 6-order equation is proved to have a better result, which is …

The main objective of my thesis is to develop a numerical model for small-scale thermal energy storage system and to see the effect of dispersing nano-particles and using fractal-like branching heat exchanger in phase change material for our proposed thermal energy storage system. The associated research problems investigated for phase change material (PCM) are the low thermal conductivity and low rate of heat transfer from heat transfer fluid to PCM in thermal energy storage system. In this study an intensive study is carried out to find the best material for thermal storage and later on as a high conductive nano-particle graphite is used to enhance the effective thermal conductivity of the mixed materials. As a thermal storage material molten solar Salt (60% NaNO3+40%KNO3) has been selected, after that detailed numerical modeling of the proposed design has been done using MATLAB algorithm and following the fixed grid enthalpy method. The model is based on the numerical computation of 1-D finite difference method using explicit scheme. The second part of the study is based on enhancing the heat transfer performance by introducing the concept of fractal network or branching heat exchanger. Results from the numerical computation have been utilized for the comparison …

The purpose of this investigation is to find out suitability of the solar chimney natural ventilation system in a Zero Energy Lab located at the University of North Texas campus, to figure out performance of the solar chimney. Reduction in the heating and ventilation and air conditioning energy consumption of the house has been also analyzed. The parameters which are considered for investigation are volumetric flow rate of outlet of chimney, the absorber wall temperature and glass wall temperatures. ANSYS FLUENT 14.0 has been employed for the 3-D modeling of the solar chimney. The dimensions of the solar chimney are 14’2” X 7’4” X 6’11”. The flow inside solar chimney is found to be laminar and the simulation results show that maximum outlet volumetric flow rate of about 0.12m3/s or 432 cfm is possible from chimney. The experimental velocity of chimney was found to be 0.21 m/s. Density Boussinesq approximation is considered for the modeling. Velocity and temperature sensors have been installed at inlet and outlet of the chimney in order to validate the modeling results. It is found that based on simulated volumetric flow rate that cooling load of 9.29 kwh can be saved and fan power of 7.85 …