UNT Theses and Dissertations - 62 Matching Results

Search Results

Note: All results matching your query require you to be a member of the UNT Community (you must be on campus or login with university credentials for access).

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

Description: 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 of 130 Hz. Initially high impedance of mutant sample tended to drop within 2 hours and finally approached the constant value which signified that the cell death mechanism was complete. However, the wildtype sample demonstrated approximately constant impedance (conductivity) during the experiment.
Date: August 2010
Creator: Abtahi, Seyed Ali
Partner: UNT Libraries

Sustainable Energy Solutions for Water Purification Applications: Municipal and Industrial Case Studies

Description: In several areas around the world, clean water is a precious asset that at anytime, and mainly due to circumstances of weather and climate, can become scarce. Mainly in the dry and remote places, people suffer with lack of water. A solution for this suffering can be a water desalination system, which makes water potable and usable for industry. That solution inherently, brings the problem of power requirement, which is sometimes arduous to accomplish in such remote areas of difficult access and long distances to overcome to build the infrastructure required to operate an electric power plant. Texas and the USA also face this scenario for many regions, for which the government has been creating some programs and driving forward incentives, looking for solutions to support water desalination. Water desalination has future applications for municipalities water-consuming or for arid and remote regions, as well as for industries that rely on heavy water usage, such as natural gas drilling operations, for which millions of gallons are trucked overland to the site and also hauled away afterwards, when the waste water produced must be treated. This thesis created the concept of autonomy for water desalination plants replacing the actual power supply from fossil fuel to a renewable source from wind or sun, giving capacity to them to produce its own electricity to operate as an autonomous unit, as demonstrated in the business case done for the Brownsville water desalination facility.
Date: May 2014
Creator: Mira, Sebastião Bittencourt de
Partner: UNT Libraries

Performance Analysis of Two Alternative Hvac Systems for the Unt Zero Energy Lab

Description: This paper covers the simulation and comparison among three different HVAC (heating, ventilation & air conditioning)systems to achieve the goal of finding the most effective HVAC among these three in terms of human comfort, efficiency and cost considering North Texas climate. In the Zero Energy Lab at the University of North Texas, Denton, TX, the HVAC system of the building assembles with geothermal heat source. Here, water to water heat pump with radiant floor and water to air heat pump with air ducts provide heating & cooling of the building. In this paper electricity consumption, comfort, cost & efficiency analysis is done for the existing system using Energy Plus simulation software. Calibration of the simulated data of the existing system is done comparing with the actual data. Actual data is measured using 150 sensors that installed in Zero Energy Lab. After the baseline model calibration, simulation for ground source water to water heat pump, evaporative cooler with baseboard electric heater and water cooled electric chiller with baseboard electric heater (as a conventional system) is shown. Simulation results evaluate the life cycle cost (LCC) for these HVAC systems. The results of the comparison analysis among all the three HVAC systems show the most effective HVAC system among these three systems in North Texas weather. The results will make UNT Zero Energy lab a standard model towards a sustainable green future.
Date: August 2013
Creator: Hasib, Naimee
Partner: UNT Libraries

Thermally Stimulated Depolarization Current Evaluation of Molding Compounds

Description: 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.
Date: May 2014
Creator: Zhao, Shunli
Partner: UNT Libraries

Sensitivity and Uncertainty Analysis of Occupancy-related Parameters in Energy Modeling of Unt Zero Energy Lab

Description: 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 around 0.1% compared with real value.
Date: August 2013
Creator: Xiong, Guangyuan
Partner: UNT Libraries

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

Description: 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 were other major contributors in the area; Flaring operations, solvents, and petrochemicals also impacted the measured VOC in the urban area. It was noted that he measured VOC concentrations were significantly influenced by the economic downturn in the region and this was highlighted in the annual trends of the apportioned VOC.
Date: May 2014
Creator: Abood, Ahmed T.
Partner: UNT Libraries

Effect of Dispersed Particles and Branching on the Performance of a Medium Temperature Thermal Energy Storage System

Description: 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 between a conventional heating system (with a simple single tube as a heat exchanger) and a passive PCM thermal energy storage system with branching heat exchanger using NTU-effectiveness method and charging time calculation. The comparison results show a significant amount improvement using branching network and mixing nano-particle in terms of heat transfer (13.5% increase in effectiveness of branching level-02 heat exchangers from the conventional one ), thermal conductivity (increased 73.6% with 20% graphite nano-particle mix with solid PCM), charging time (57% decrease of charging time for the effect of both the dispersion of Graphite nano-particle and branching heat exchange) and ...
Date: August 2013
Creator: Hasib, A. M. M. Golam
Partner: UNT Libraries

A Performance Analysis of Solar Chimney Passive Ventilation System in the Unt Zero Energy Lab

Description: 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 Watts can be saved.
Date: August 2013
Creator: Talele, Suraj H.
Partner: UNT Libraries

Electromagnetic Shielding Properties of Iron Oxide Impregnated Kenaf Bast Fiberboard

Description: 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%, 65-75% and 70-80%, respectively.
Date: December 2014
Creator: Ding, Zhiguang
Partner: UNT Libraries

Microchannel Radiator: an Investigation of Microchannel Technology with Applications in Automotive Radiator Heat Exchangers

Description: 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 demonstrate the heat transfer and pressure drop of microchannel tubes. The results confirmed that heat transfer of microchannels does improve the thermal performance of the radiator but the pressure drop is such that the net benefit does not outweigh the operating cost. An additional CFD study of the new fin geometry and air-side heat transfer predictions was conducted. The results of the study confirmed the theoretical calculations for the fin geometry.
Date: August 2014
Creator: Checketts, Gus Thomas
Partner: UNT Libraries

Analyze and Rebuild an Apparatus to Gauge Evaporative Cooling Effectiveness of Micro-Porous Barriers.

Description: The sample used for evaporative cooling system is Fabric defender 750 with Shelltite finish. From the experimental data and equations we have diffusion coefficient of 20.9 ± 3.71 x 10-6 m2/s for fabric with one layer with 17%-20% fluctuations from the theory, 27.8 ± 4.5 x 10-6 m2/s for fabric with two layers with 6%-14% fluctuations from the theory and 24.9 ± 4.1 x 10-6 m2/s for fabric with three layers with 13%-16% fluctuations from the theory. Since the thickness of the fabric increases so the mass transport rate decreases so the mass transport resistance should be increases. The intrinsic mass resistances of Fabri-1L, Fabri-2L and Fabri-3L are respectively 104 ± 10.2 s/m, 154 ± 23 s/m and 206 ± 26 s/m from the experiment.
Date: December 2008
Creator: Mohiti Asli, Ali
Partner: UNT Libraries

Errors in skin temperature measurements.

Description: Numerical simulation is used to investigate the accuracy of a direct-contact device for measuring skin-surface temperature. A variation of thermal conductivity of the foam has greater effect on the error rather than a variation of the blood perfusion rate. For a thermal conductivity of zero, an error of 1.5 oC in temperature was identified. For foam pad conductivities of 0.03 and 0.06 W/m-oC, the errors are 0.5 and 0.15 oC. For the transient study, with k=0 W/m-oC, it takes 4,900 seconds for the temperature to reach steady state compared with k=0.03 W/m-oC and k=0.06 W/m-oC where it takes 3,000 seconds. The configuration without the foam and in presence of an air gap between the skin surface and the sensor gives the most uniform temperature profile.
Date: December 2008
Creator: Dugay, Murielle
Partner: UNT Libraries

Estimation of Air Emissions During Production Phase from Active Oil and Gas Wells in the Barnett Shale Basin: 2010-2013

Description: 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 period. Amongst the concerned emitted pollutants, VOC was the largest emitted pollutant during the study period (417,804 tons), followed by NOx (126,691 tons) and CO (47,884 tons). Significant Sources of air emissions include: storage tanks, wellhead compressor engines, and pneumatic devices. Storage tanks and pneumatic devices contributed to about 62% and 28% of the total VOC emissions, respectively. Whereas, wellhead compressor engines are primarily responsible for about 97% of the total NOx emissions. Finally, in Tarrant, Wise and Denton counties, the emissions increased during the study period due to increase in the oil and gas production, while Johnson County’s emission ...
Date: May 2015
Creator: Dohde, Farhan A.
Partner: UNT Libraries

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

Description: 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 are conducted. New effective properties for the octet-truss lattice structure are developed considering the observed behavior of the octet-truss structure under macroscopic compression and tension trough simulations.
Date: May 2015
Creator: Challapalli, Adithya
Partner: UNT Libraries

Experimental Study on Fluidization of Biomass, Inert Particles, and Biomass/Sand Mixtures

Description: Fluidization of biomass particles is an important process in the gasification, pyrolysis and combustion in order to extract energy from biomass. Studies on the fluidization of biomass particles (corn cob and walnut shell), inert particles (sand, glass bead, and alumina), which are added to facilitate fluidization of biomass, and biomass/sand mixture were performed. Experiments were carried out in a 14.5 cm internal diameter cold flow fluidization bed to determine minimum fluidization velocities with air as fluidizing medium. On the of basis of experimental data from both present work and those found in the literature, new correlations were developed to predict minimum fluidization velocity for inert particles as well as biomass particles. It was found that the proposed correlations satisfactorily predict minimum fluidization velocities and was in well agreement with experimental data. Furthermore, effect of weight percentage of biomass in the biomass/sand mixtures was studied. The weight fraction of biomass particles in the mixture was chosen in the range of 0 ~ 100 wt. %. The results show that minimum fluidization velocity of the mixtures increases with an increase in biomass content. Using the present experimental data, a new correlation was developed in terms of mass ratio for predicting values of minimum fluidization velocity of these mixtures. However, the validity of the proposed correlation should be further studied by conducting more experiments using the biomass/sand mixtures of different particle size, shape, and density.
Date: May 2011
Creator: Paudel, Basu
Partner: UNT Libraries

Energy Usage While Maintaining Thermal Comfort : A Case Study of a UNT Dormitory

Description: Campus dormitories for the University of North Texas house over 5500 students per year; each one of them requires certain comfortable living conditions while they live there. There is an inherit amount of money required in order to achieve minimal comfort levels; the cost is mostly natural gas for water and room heating and electricity for cooling, lighting and peripherals. The US Department of Energy has developed several programs to aid in performing energy simulations to help those interested design more cost effective building designs. Energy-10 is such a program that allows users to conduct whole house evaluations by reviewing and altering a few parameters such as building materials, solar heating, energy efficient windows etc. The idea of this project was to recreate a campus dormitory and try to emulate existent energy consumption then try to find ways of lowering that usage while maintaining a high level of personal comfort.
Date: December 2011
Creator: Gambrell, Dusten
Partner: UNT Libraries

High-Precision Micropipette Thermal Sensor for Measurement of Thermal Conductivity of Carbon Nanotubes Thin Film

Description: The thesis describes novel glass micropipette thermal sensor fabricated in cost-effective manner and thermal conductivity measurement of carbon nanotubes (CNT) thin film using the developed sensor. Various micrometer-sized sensors, which range from 2 µm to 30 µm, were produced and tested. The capability of the sensor in measuring thermal fluctuation at micro level with an estimated resolution of ±0.002oC is demonstrated. The sensitivity of sensors was recorded from 3.34 to 8.86 µV/oC, which is independent of tip size and dependent on the coating of Nickel. The detailed experimental setup for thermal conductivity measurement of CNT film is discussed and 73.418 W/moC was determined as the thermal conductivity of the CNT film at room temperature.
Date: August 2011
Creator: Shrestha, Ramesh
Partner: UNT Libraries

Quasi-Three Dimensional Experiments on Liquid-Solid Fluidized Bed of Three Different Particles in Two Different Distributors

Description: This thesis is an experimental study of the fluidization of binary mixture in particulate flows. A fluidized bed with two distributors was built with water being used as carrying fluid. Three types of solid particles of nylon, glass and aluminum of the same size and different densities are used in the experiments. The wall effect on a single particle fluidization, the fluidization of binary mixture of large density difference (nylon and aluminum of density ratio of 0.42), and the fluidization of binary mixture of close density (glass and aluminum with density ratio of 0.91) were investigated. Also, the effect of distributors on mono-disperse and bi-disperse particle fluidization was investigated. Results show that the presence of narrow walls reduces the minimum fluidization velocity for a single particle by as much as nearly 40%. Also, in the case of binary mixture of close density particles, uniform mixing was easily achieved and no segregation was observed, but in the case of large density difference particles, there exists significant segregation and separation. At high velocity, the uniform distributor behaves like a transport bed. To achieve a full bed in the single jet, it requires 1.5 times velocity of the uniform distributor. This behavior determines their application in the industries.
Date: December 2009
Creator: Obuseh, Chukwuyem Charles
Partner: UNT Libraries

Analysis of Sources Affecting Ambient Particulate Matter in Brownsville, Texas

Description: Texas is the second largest state in U.S.A. based on geographical area, population and the economy. It is home to several large coastal urban areas with major industries and infrastructure supporting the fossil-fuel based energy sector. Most of the major cities on the state have been impacted by significant air pollution events over the past decade. Studies conducted in the southern coastal region of TX have identified long range transport as a major contributor of particulate matter (PM) pollution along with local emissions. Biomass burns, secondary sulfates and diesel emissions sources are comprise as the dominant mass of PM2.5 have been noted to be formed by the long range transport biomass from Central America. Thus, the primary objective of this study was to identify and quantify local as well as regional sources contributing to the PM pollution in the coastal area of Brownsville located along the Gulf of Mexico. Source apportionment techniques such as principal component analysis (PCA) and positive matrix factorization (PMF) were employed on the air quality monitoring data to identify and quantify local and regional sources affecting this coastal region. As a supplement to the PMF and PCA, conditional probability function (CPF) analysis and potential source contribution function (PSCF) analysis were employed to characterize the meteorological influences for PM events. PCA identified an optimal solution of 6 sources affecting the coastal area of Brownsville, while PMF resolved 8 sources for the same area. Biomass comingled with sea salt was identified to be the dominant contributor from the PCA analysis with 30.2% of the apportioned PM mass in Brownsville, meanwhile PMF account secondary sulfates I & II with 27.6%. the other common sources identified included, biomass burning, crustal dust, secondary sulfate, oil combustion, mobile sources and miscellaneous traffic sources.
Date: May 2012
Creator: Diaz Poueriet, Pablo
Partner: UNT Libraries

Simulation Study of Tremor Suppression and Experiment of Energy Harvesting with Piezoelectric Materials

Description: The objective of this research is to develop a wearable device that could harvest waste mechanical energy of the human hand movement and utilize this energy to suppress wrist tremors. Piezoelectric material is used to measure the hand movement signals, and the signal of wrist tremor is filtered to be utilized to suppress the tremor. In order to conduct the experiment of energy harvesting and tremor suppression, an experimental rig was fabricated. Two types of piezoelectric materials, PVDF (polyvinylidene fluoride) films and MFC (macro fiber composite) films, are used to harvest mechanical energy and used as actuators to suppress hand tremors. However, due to some shortages of the materials, these two types of materials are not used as actuators to suppress the wrist tremors. Thus, we use Matlab Simulink to simulate the tremor suppression with AVC (active vibration control) algorithm.
Date: August 2012
Creator: Ou, Jianqiang
Partner: UNT Libraries

Quantification of Anthropogenic and Natural Sources of Fine Particles in Houston, Texas Using Positive Matrix Factorization

Description: Texas, due to its geographical area, population, and economy is home to a variety of industrialized areas that have significant air quality problems. These urban areas are affected by elevated levels of fine particulate matter (PM2.5). The primary objective of this study was to identify and quantify local and regional sources of air pollution affecting the city of Houston, Texas. Positive Matrix Factorization (PMF) techniques were applied to observational datasets from two urban air quality monitoring sites in Houston from 2003 through 2008 in order to apportion sources of pollutants affecting the study region. Data from 68 species for Aldine and 91 for Deer Park were collected, evaluated, and revised to create concentration and uncertainty input files for the PMF2 and EPA PMF (PMF3) source apportionment models. A 11-sources solution for Aldine and 10-sources for Deer Park were identified as the optimal solutions with both models. The dominant contributors of fine particulate matter in these sites were found to be biomass burnings (2%-8.9%), secondary sulfates I (21.3%-7.6%) and II (38.8%-22.2%), crustal dust (8.9%-10.9%), industrial activities (10.9%-4.2%), traffic (23.1%-15.6%), secondary nitrates (4.4%-5.5%), fresh (1%-1.6%) and aged(5.1%-4.6%) sea salt and refineries (1.3%-0.6%), representing a strong case to confirm the high influence of local activities from the industrial area and the ship channel around the Houston channel. Additionally, potential source contribution function (PSCF) and conditional probability function (CPF) analyses were performed to identify local and regional source-rich areas affecting this urban airshed during the study period. Similarly, seasonal variations and patterns of the apportioned sources were also studied in detail.
Date: August 2012
Creator: Peña Sanchez, Carlos Alberto
Partner: UNT Libraries

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

Description: 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 EnergyPlus simulations, when the conventional structure insulated panel (SIP) in the roof and wall structures were replaced by the herb panel or herb/PCM composite, it was found that around 16.0% of energy savings in heating load and 11.0% in cooling load were obtained by using PCM in the bio-product porous medium.
Date: August 2018
Creator: Boozula, Aravind Reddy
Partner: UNT Libraries

Heat Transfer in Low Dimensional Materials Characterized by Micro/Nanoscale Thermometry

Description: 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 substrate was calculated by MD simulation.As another low dimensional material for thermal management applications, the thermal conductivity of BNNT was measured by nanoscale thermometry. For this work, a noble technique combining a focused ion beam (FIB) and nanomanipulator was employed to pick and to place a single BNNT on the desired location. The FIB technology was used to make nanoheater patterns (so called nanothermometer) on a prefabricated microelectrode device by conventional photolithography processes. With this noble technique and the nanoheater thermometry, the thermal conductivity of BNNT was successfully characterized by temperature gradient and heat flow measurements through BNNT.
Date: August 2018
Creator: Jeong, Jae Young
Partner: UNT Libraries

Analysis of Heat Transfer Enhancement in Channel Flow through Flow-Induced Vibration

Description: 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 only reduced the surface wall temperature by 3% compared to the channel without any cylinders because the volume of the second cylinder could occupy some space, and therefore, reduce the effect of the convective heat transfer. By reducing the diameter of the second cylinder by 25% increased the effect of the convection heat transfer and reduced the maximum wall temperature by around 15%. Compared to the channel with no cylinder, the introduction of cylinders into the channel flow was found to increase the average Nusselt number by 55% with the insertion of a stationary rigid cylinder, by 85% with the ...
Date: December 2017
Creator: Kota, Siva Kumar k
Partner: UNT Libraries