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Pages
- Title
- Implementation of Optical Interferometry and Spectral Reflectometry for High Fidelity Thin Film Measurements.
- Creator
-
Arends-Rodriguez, Armando, Putnam, Shawn, Chow, Louis, Kauffman, Jeffrey, University of Central Florida
- Abstract / Description
-
An in-house reflectometer/interferometer has been built to investigate the varying curvature and thickness profiles in the contact line region of air, acetone, iso-octane, ethanol, and water on various types of substrates. Light intensity measurements were obtained using our reflectometer/interferomter and then analyzed in MATLAB to produce thickness and curvature profiles. The apparatus is based on the principle of a reflectometer, consisting of different optical elements, probe, light...
Show moreAn in-house reflectometer/interferometer has been built to investigate the varying curvature and thickness profiles in the contact line region of air, acetone, iso-octane, ethanol, and water on various types of substrates. Light intensity measurements were obtained using our reflectometer/interferomter and then analyzed in MATLAB to produce thickness and curvature profiles. The apparatus is based on the principle of a reflectometer, consisting of different optical elements, probe, light source, and spectrometer. Our reflectometer/interferomter takes measurements in the UV-Vis-IR range (200nm-1000nm). This range is achieved by using a light source that has both a deuterium light (190nm-800nm), a tungsten halogen light (400nm-1100nm), a Metal-Core Printed Circuit Board LED (800nm-1000nm) and a Metal-Core Printed Circuit board cold white LED (400nm-800nm, 6500 K). A UV-VIS-IR spectrometer reads the light response after light is focused on the region of interest. Then a CCD camera (2448x2048) records the profiles for image analyzing interferometry. The readings were then validated based on results in the literature and studies with cylindrical lens samples.
Show less - Date Issued
- 2017
- Identifier
- CFE0006559, ucf:51328
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006559
- Title
- Simulation of Heat/Mass Transfer of a Three-Layer Impingement/Effusion Cooling System.
- Creator
-
Smith, Brandon, Chow, Louis, Wu, Xinzhang, Deng, Weiwei, University of Central Florida
- Abstract / Description
-
Cooling techniques for high density electrical components and electronic devices have been studied heavily in recent years. The advancements in the electrical/electronic industry have required methods of high heat flux removal. Many of the current electrical components and electronic devices produce a range of heat fluxes from 20 W/cm2 (-) 100 W/cm2. While parallel flow cooling systems have been used in the past, jet impingement is now more desirable for its potential to have a heat transfer...
Show moreCooling techniques for high density electrical components and electronic devices have been studied heavily in recent years. The advancements in the electrical/electronic industry have required methods of high heat flux removal. Many of the current electrical components and electronic devices produce a range of heat fluxes from 20 W/cm2 (-) 100 W/cm2. While parallel flow cooling systems have been used in the past, jet impingement is now more desirable for its potential to have a heat transfer coefficient 3-5 times greater than that of parallel flow at the same flow rate. Problems do arise when the jet impingement is confined and a cross flow develops that interacts with impinging jets downstream leading to a decrease in heat transfer coefficient. For long heated surfaces, such as an aircraft generator rotor, span wise fluid management is important in keeping the temperature distribution uniform along the length of the surface. A detailed simulation of the heat/mass transfer on a three-layer impingement/effusion cooling system has been conducted. The impingement jet fluid enters from the top layer into the bottom layer to impinge on the heated surface. The spent fluid is removed from the effusion holes and exits through the middle layer. Three different effusion configurations were used with effusion diameters ranging from 0.5 mm to 2 mm. Temperature uniformity, heat transfer coefficients, and pressure drops were compared for each effusion diameter arrangement, jet to target spacing (H/d), and rib configuration. A Shear Stress Transport (SST) turbulence fluid model was used within ANSYS CFX to simulate all design models. Three-layer configurations were also set in series for long, rectangular heated surfaces and compared against traditional cooling methods such as parallel internal flow and traditional jet impingement models. The results show that the three-layer design compared to a traditional impingement cooling scheme over an elongated heated surface can increase the average heat transfer coefficient by 75% and reduce the temperature difference on the surface by 75%. It was shown that for a three layer design under the same impingement geometry, the average heat transfer coefficient increases when H/d is small. The inclusion of ribs always provided better heat transfer and centralized the cooling areas. The heat transfer was increased by as much as 25% when ribs were used. The effusion hole arrangement showed minimal correlation to heat transfer other than a large array provides better results. The effusion holes' greatest impact was found in the pressure drop of the cooling model. The pressure losses were minimal when the effective area of effusion holes was large. This minimizes the losses due to contraction and expansion.
Show less - Date Issued
- 2012
- Identifier
- CFE0004795, ucf:49720
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004795
- Title
- Study of Transport Phenomena in Carbon-Based Materials.
- Creator
-
Aboelsoud, Walid, Chow, Louis, Kumar, Ranganathan, Deng, Weiwei, Kar, Aravinda, University of Central Florida
- Abstract / Description
-
In air-cooled heat exchangers, air-side thermal resistance is usually the largest compared to conduction and liquid-side thermal resistances. Thus, reducing the air-side thermal resistance with fin-like structures can greatly improve overall cooling performance. The performance of these structures is usually characterized by the rate of heat which can be transferred and the pumping power required. One promising solution is to use a high-thermal-conductivity material with a large surface per...
Show moreIn air-cooled heat exchangers, air-side thermal resistance is usually the largest compared to conduction and liquid-side thermal resistances. Thus, reducing the air-side thermal resistance with fin-like structures can greatly improve overall cooling performance. The performance of these structures is usually characterized by the rate of heat which can be transferred and the pumping power required. One promising solution is to use a high-thermal-conductivity material with a large surface per unit volume such as carbon foam. This study presents a method of utilizing V-shape corrugated carbon foam. The air-side heat transfer coefficient and the pressure drop across the foam have been investigated using different V-shape foam geometrical configurations obtained by varying its length and height. Based on design considerations and availability, the foam length has been chosen to be 25.4, 38.1 and 52.1 mm while its height is 4.4, 6.8 and 11.7 mm, resulting in nine different test pieces of foam with different heights and lengths.A total number of 81 experiments were carried out and results show that of the nine V-shape configurations, the foam with the shortest length and tallest height gives the best performance. Experimental results are also compared with the results of prior work using different carbon foam geometries. It is shown that V-shape corrugated carbon foam provides higher heat transfer coefficient and better overall performance.Numerical method is performed next. The effect of the foam length and height on thermal and hydraulic performance is demonstrated and discussed. There is excellent agreement between numerical and experimental results. An analysis is also made to better understand the transport phenomena that occur within the porous matrix. For laminar flow of air, one of the findings is the high heat transfer effectiveness of the foam which means a foam thickness of 1 mm or less is sufficient for heat transfer enhancement for air speed of up to 4 m/s. To demonstrate the feasibility of using carbon foam, an analytical case study of carbon foam heat exchanger was performed and compared to traditional heat exchanger with the same heat load. Results show that a volume saving of up to 55% can be obtained by using carbon foam instead of traditional aluminum fins.Another attractive carbon-based material is the highly oriented pyrolytic graphite (HOPG) which has an in-plane thermal conductivity of about 1700 W/m.K and an out-of-plane k of about 8 W/m.K at room temperature. HOPG is a graphite material with a high degree of preferred crystallographic orientation. HOPG can be very useful in thermal applications when axial conduction is critical and needed to be minimized as in recuperators used in cryocoolers and compact power generation. Also, an analysis of HOPG for micro-channel applications shows that the high in-plane thermal conductivity of HOPG, which is far greater than that of copper and aluminum, allows a taller height for the micro-channel. This translates to an increase in the heat flux removal rate by two to three times.
Show less - Date Issued
- 2013
- Identifier
- CFE0005081, ucf:50732
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005081
- Title
- Computational Fluid Dynamics Investigation of A Novel Hybrid Comprehensive Stage II Operation For Single Ventricle Palliation.
- Creator
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Hameed, Marwan, Kassab, Alain, DeCampli, William, Chow, Louis, Mansy, Hansen, Divo, Eduardo, University of Central Florida
- Abstract / Description
-
Single ventricle (SV) anomalies account for one(&)#226;€"fourth of all cases of congenital heart disease. The existingthree hybrid staged surgical approach serving as a palliative treatment for this anomaly entails multiple complicationsand achieves a survival rate of only 50%. To reduce trauma associated with the second stage of the hybrid procedure,the hybrid comprehensive stage 2 (HCS2) operation was introduced in 2014 at Arnold Palmer Hospital in Orlando as anovel palliation alternative...
Show moreSingle ventricle (SV) anomalies account for one(&)#226;€"fourth of all cases of congenital heart disease. The existingthree hybrid staged surgical approach serving as a palliative treatment for this anomaly entails multiple complicationsand achieves a survival rate of only 50%. To reduce trauma associated with the second stage of the hybrid procedure,the hybrid comprehensive stage 2 (HCS2) operation was introduced in 2014 at Arnold Palmer Hospital in Orlando as anovel palliation alternative for a select subset of SV patients with adequate antegrade aortic flow. It avoids dissection ofthe pulmonary arteries by introducing a stented intrapulmonary baffle and avoids reconstruction of the aortic arch bymaintaining patency of the ductus arteriosus. This dissertation aims to provide better insight on the post-operativehemodynamics of HCS2 patients. A multi-scale Computational Fluid Dynamics (CFD) analysis of a synthetic,patient-derived HCS2 geometry based on unsteady laminar flow conditions and a non(&)#226;€"Newtonian blood model isutilized to quantify the resultant hemodynamics. The 3D CFD model is coupled to a 0D lumped parameter modelof the peripheral circulation that supplies the boundary conditions necessary to run the CFD analyses of the HCS2. Based on clinical parameters suggesting the baffle related narrowing to be at minimum 10mm and the pressuregradient not surpassing 20mmHg, hemodynamic analysis reveals that for even a 7.23mm narrowing the averagepressure drop across the baffle is 0.53mmHg. A peak pressure drop of 2.96mmHg was computed over the investigatedrange of clearances over the pulmonary baffle. Vortex shedding presents no concerns as the distance between the baffleand the aortic arch is much smaller compared to the length required for full vortices to form. Uneven contour distributionof the wall shear stress was observed due to the bend presented by the baffle that strongly affects the velocity profile inthe lumen across the pulmonary trunk and into the ductus arteriosus. Moreover, an oxygen transport model was derived,and the results showed consistency with the published data of Glenn patients. Particle residence time was also reported toidentify any blood recirculation or flow stagnation that may lead to platelet activation leading to clot formation rate.The study provides a range of main pulmonary artery geometries that, following multi-scale CFD analysis, present noconcerns regarding excessive pressure gradients or vortex formation. Moreover, the model identifies locations ofpotentially problematic hemodynamics that could be mitigated by shape optimization of the reconstruction.
Show less - Date Issued
- 2019
- Identifier
- CFE0007813, ucf:52340
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007813
- Title
- A study of organo-phosphorous simulants thermal destruction using shock tube/laser diagnostics techniques and chemical kinetics modeling.
- Creator
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Neupane, Sneha, Vasu Sumathi, Subith, Kassab, Alain, Chow, Louis, Peale, Robert, University of Central Florida
- Abstract / Description
-
High-fidelity chemical kinetic models are critical in predictive modeling during design and optimization of next generation energy systems. Shock tube provides an ideal tool to investigate high-temperature chemical kinetics. Non-intrusive laser absorption diagnostics provide in-situ measurements of quantitative, time-resolved species concentration data in this complex chemically reacting system. In this work, shock tube and laser absorption spectroscopy were utilized to measure species...
Show moreHigh-fidelity chemical kinetic models are critical in predictive modeling during design and optimization of next generation energy systems. Shock tube provides an ideal tool to investigate high-temperature chemical kinetics. Non-intrusive laser absorption diagnostics provide in-situ measurements of quantitative, time-resolved species concentration data in this complex chemically reacting system. In this work, shock tube and laser absorption spectroscopy were utilized to measure species concentration time-histories during pyrolysis and oxidation of organo-phosphorous compounds (OPCs). The experiments data obtained were used as benchmark to develop an improved kinetic model of OPCs combustion. Interest in combustion chemistry of OPCs is associated to their use as fire suppressants and as chemical weapons. Pyrolysis and oxidation of OPCs were carried out behind reflected shock wave and laser absorption spectroscopy utilizing quantum cascade laser at mid-IR wavelength region was used to measure time resolved intermediate CO concentration produced during the process. Utilizing the experiments data, an improved chemical kinetic model for combustion of an OPC (-) Triethyl Phosphate (TEP) was developed. Various steps taken to develop the improved model include: calculation of thermochemical properties; updating hydrocarbon kinetics; calculation of reaction rates and addition of alternative TEP decomposition pathways. The prediction of TEP combustion, in terms intermediate CO concentration yield during its pyrolysis and oxidation, made by the improved model is in much better agreement with the experiments. Such an accurate kinetic model is critical in predicting the effectiveness of OPCs as flame retardants when used as dopants in hydrocarbon fuels; and in devising counter weapon of mass destruction strategies to destroy chemical weapons.
Show less - Date Issued
- 2019
- Identifier
- CFE0007691, ucf:52444
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007691
- Title
- Numerical Simulation of Conventional Fuels and Biofuels Dispersion and Vaporization Process in Co-flow and Cross-flow Premixers.
- Creator
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Gu, Xin, Kumar, Ranganathan, Basu, Saptarshi, Kapat, Jayanta, Chow, Louis, Shivamoggi, Bhimsen, University of Central Florida
- Abstract / Description
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In order to follow increasingly strict regulation of pollutant emissions, a new concept of Lean Premixed pre-vaporized (LPP) combustion has been proposed for turbines. In LPP combustion, controlled atomization, dispersion and vaporization of different types of liquid fuel in the pre-mixer are the key factors required to stabilize the combustion process and improve the efficiency. A numerical study is conducted for the fundamental understanding of the liquid fuel dispersion and vaporization...
Show moreIn order to follow increasingly strict regulation of pollutant emissions, a new concept of Lean Premixed pre-vaporized (LPP) combustion has been proposed for turbines. In LPP combustion, controlled atomization, dispersion and vaporization of different types of liquid fuel in the pre-mixer are the key factors required to stabilize the combustion process and improve the efficiency. A numerical study is conducted for the fundamental understanding of the liquid fuel dispersion and vaporization process in pre-mixers using both cross-flow and co-flow injection methods. First, the vaporization model is validated by comparing the numerical data to existing experiments of single droplet vaporization under both low and high convective air temperatures. Next, the dispersion and vaporization process for biofuels and conventional fuels injected transversely into a typical simplified version of rectangular pre-mixer are simulated and results are analyzed with respect to vaporization performance, degree of mixedness and homogeneity. Finally, collision model has been incorporated to predict more realistic vaporization performance. Four fuels, Ethanol, Rapeseed Methyl Esters (RME), gasoline and jet-A have been investigated. For mono-disperse spray with no collision model, the droplet diameter reduction and surface temperature rise were found to be strongly dependent on the fuel properties. The diameter histogram near the pre-mixer exit showed a wide droplet diameter distribution for all the fuels. In general, pre-heating of the fuels before injection improved the vaporization performance. An improvement in the drag model with Stefan flow correction showed that a low speed injection and high cone angle improved performance. All fuels achieved complete vaporization under a spray cone angle of 140(&)deg;. In general, it was found that cross-flow injection achieved better vaporization performance than co-flow injection. A correlation is derived for jet-A's total vaporization performance as a function of non-dimensional inlet air temperature and fuel/air momentum flux ratio. This is achieved by curve-fitting the simulated results for a broad range of inlet air temperatures and fuel/air momentum flux ratios. The collision model, based on no-time-counter method (NTC) proposed by Schmidt and Rutland, was implemented to replace O'Rourke's collision algorithm to improve the results such that the unphysical numerical artifact in a Cartesian grid was removed and the results were found to be grid-independent. The dispersion and vaporization processes for liquid fuel sprays were simulated in a cylindrical pre-mixer using co-flow injection method. Results for jet-A and Rapeseed Methyl Esters (RME) showed acceptable grid independence. At relatively low spray cone angle and injection velocity, it was found that the collision effect on the average droplet size and the vaporization performance were very high due to relatively high coalescence rate induced by droplet collisions. It was also found that the vaporization performance and the level of homogeneity of fuel-air mixture could be significantly improved when the dispersion level is high, which can be achieved by increasing the spray cone angle and injection velocity. In order to compare the performance between co-flow and cross-flow injection methods, the fuels were injected at an angle of 40(&)deg; with respect to the stream wise direction to avoid impacting on the wall. The cross-flow injection achieved similar vaporization performance as co-flow because a higher coalescence rate induced by droplet collisions cancelled off its higher heat transfer efficiency between two phases for cross-flow injections.
Show less - Date Issued
- 2012
- Identifier
- CFE0004192, ucf:49004
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004192
- Title
- Characterization, Morphology, Oxidation, and Recession of Silicon Nanowires Grown by Electroless Process.
- Creator
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Mertens, Robert, Sundaram, Kalpathy, Yuan, Jiann-Shiun, Chow, Louis, Wahid, Parveen, Blair, Richard, University of Central Florida
- Abstract / Description
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This dissertation presents heretofore undiscovered properties of Silicon Nanowires (SiNWs) grown by electroless process and presents mathematical solutions to the special problems of the oxidation and diffusion of dopants for SiNWs. Also presented here is a mathematical description of morphology of oxidized SiNWs. This dissertation is comprised of several discussions relating to SiNWs growth, oxidation, morphology and doping.In here is presented work derived from a long-term study of SiNWs....
Show moreThis dissertation presents heretofore undiscovered properties of Silicon Nanowires (SiNWs) grown by electroless process and presents mathematical solutions to the special problems of the oxidation and diffusion of dopants for SiNWs. Also presented here is a mathematical description of morphology of oxidized SiNWs. This dissertation is comprised of several discussions relating to SiNWs growth, oxidation, morphology and doping.In here is presented work derived from a long-term study of SiNWs. Several important aspects of SiNWs were investigated and the results published in journals and conference papers. The recession of SiNWs was heretofore unreported by other research groups. In our investigations, this began as a question, (")How far into the substrate does the etching process go when this method is used to make SiNWs?(") Our investigations showed that recession did take place, was controllable and that a number of variables were responsible. The growth mechanism of SiNWs grown by electroless process is discussed at length. The relation of exposed area to volume of solution is shown, derived from experimentation. A relation of Silver used to Si removed is presented, derived from experimentation. The agglomeration of SiNWs grown by the electroless process is presented.The oxidation of SiNWs is a subject of interest to many groups, although most other groups work with SiNWs grown by the VLS process, which is more difficult, time-consuming and expensive to do. The oxidation of planar Silicon (Si) is still a subject of study, even today, after many years of working with and refining our formulae, because of the changing needs of this science and industry. SiNWs oxidation formulae are more complicated than those for planar Si, partly because of their morphology and partly because of their scale. While planar Si only presents one orientation for oxidation, SiNWs present a range of orientations, usually everything between (<)100(>) and (<)110(>) ( the (<)111(>) orientation is usually not presented during oxidation). This complicates the post-oxidation morphology to the extent that, subsequent to oxidation, SiNWs are more rectangular than cylindrical in shape. After etching to remove an oxidation layer from the SiNWs, the rectangular shape shifts 90(&)deg; in orientation.In traditional oxidation, the Deal-Grove formulae are used, but when the oxidation must take place in very small layers, such as with nanoscale devices, the Massoud formulae have to be used. However, even with Massoud, these formulae are not as good because of the morphology. Deal-Grove and Massoud formulae are intended for use with planar Si. We present some formulae that show the change in shape of SiNWs during oxidation, due to their morphology.The diffusion of dopants in SiNWs is a subject few research groups have taken up. Most of the groups who have, use SiNWs grown by the VLS method to make measurements and report findings. In order to measure the diffusion of dopants in SiNWs, a controllable diameter is needed. There are a number of ways to measure diffusion in SiNWs, but none of the ones used so far apply well to SiNWs grown by electroless process. Usually these groups present some mathematical formulae to predict diffusion in SiNWs, but these seem to lack mathematical rigor. Diffusion is a process that is best understood using Fick's Laws, which are applied to the problem of SiNWs in this dissertation.Diffusion is a science with a long history, going back at least 150 years. There are many formulae that can be used in the most common diffusion processes, but the processes involved with the diffusion of dopants in SiNWs is more complex than the simple diffusion processes that are fairly well-understood. Diffusion doping of SiNWs is a multiphase process that is more complex, first because it is multiphase and second because the second step involves a multiplicity of diffusing elements, plus oxidation, which brings on the problems of moving boundaries.In this dissertation, we present solutions to these problems, and the two-step diffusion process for SiNWs.
Show less - Date Issued
- 2012
- Identifier
- CFE0004412, ucf:49366
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004412
- Title
- Ytterbium-doped fiber-seeded thin-disk master oscillator power amplifier laser system.
- Creator
-
Willis-Ott, Christina, Richardson, Martin, Schulzgen, Axel, Delfyett, Peter, Chow, Louis, University of Central Florida
- Abstract / Description
-
Lasers which operate at both high average power and energy are in demand for a wide range of applications such as materials processing, directed energy and EUV generation. Presented in this dissertation is a high-power 1 ?m ytterbium-based hybrid laser system with temporally tailored pulse shaping capability and up to 62 mJ pulses, with the expectation the system can scale to higher pulse energies. This hybrid system consists of a low power fiber seed and pre-amplifier, and a solid state thin...
Show moreLasers which operate at both high average power and energy are in demand for a wide range of applications such as materials processing, directed energy and EUV generation. Presented in this dissertation is a high-power 1 ?m ytterbium-based hybrid laser system with temporally tailored pulse shaping capability and up to 62 mJ pulses, with the expectation the system can scale to higher pulse energies. This hybrid system consists of a low power fiber seed and pre-amplifier, and a solid state thin-disk regenerative amplifier. This system has been designed to generate high power temporally tailored pulses on the nanosecond time scale. Temporal tailoring and spectral control are performed in the low power fiber portion of the system with the high pulse energy being generated in the regenerative amplifier. The seed system consists of a 1030 nm fiber-coupled diode, which is transmitted through a Mach-Zehnder-type modulator in order to temporally vary the pulse shape. Typical pulses are 20-30 ns in duration and have energies of ~0.2 nJ from the modulator. These are amplified in a fiber pre-amplifier stage to ~100 nJ before being used to seed the free-space Yb:YAG thin-disk regenerative amplifier. Output pulses have maximum demonstrated pulse energies of 62 mJ with 20 ns pulse after ~250 passes in the cavity. The effects of thermal distortion in laser and passive optical materials are also. Generally the development of high power and high energy lasers is limited by thermal management strategies, as thermally-induced distortions can degrade laser performance and potentially cause catastrophic damage. Novel materials, such as optical ceramics, can be used to mitigate thermal distortions; however, thorough analysis is required to optimize their fabrication and minimize thermal distortions. Using a Shack-Hartmann wavefront sensor (SHWFS), it is possible to analyze the distortion induced in passive and doped optical elements by high power lasers. For example, the thin-disk used in the regenerative amplifier is examined in-situ during CW operation (up to 2 kW CW pump power). Additionally, passive oxide-based optical materials and Yb:YAG optical ceramics are also examined by pumping at 2 and 1 ?m respectively to induce thermal distortions which are analyzed with the SHWFS. This method has been developed as a diagnostic for the relative assessment of material quality, and to grade differences in ceramic laser materials associated with differences in manufacturing processes and/or the presence of impurities. In summation, this dissertation presents a high energy 1 ?m laser system which is novel in its combination of energy level and temporal tailoring, and an analysis of thermal distortions relevant to the development of high power laser systems.
Show less - Date Issued
- 2013
- Identifier
- CFE0004961, ucf:49588
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004961
- Title
- Deposition and characterization studies of boron carbon nitride (BCN) thin films prepared by dual target sputtering.
- Creator
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Prakash, Adithya, Sundaram, Kalpathy, Kapoor, Vikram, Yuan, Jiann-Shiun, Jin, Yier, Chow, Louis, University of Central Florida
- Abstract / Description
-
As complementary metal-oxide semiconductor (CMOS) devices shrink to smaller size, the problems related to circuit performance such as critical path signal delay are becoming a pressing issue. These delays are a result of resistance and capacitance product (RC time constant) of the interconnect circuit. A novel material with reduced dielectric constants may compromise both the thermal and mechanical properties that can lead to die cracking during package and other reliability issues. Boron...
Show moreAs complementary metal-oxide semiconductor (CMOS) devices shrink to smaller size, the problems related to circuit performance such as critical path signal delay are becoming a pressing issue. These delays are a result of resistance and capacitance product (RC time constant) of the interconnect circuit. A novel material with reduced dielectric constants may compromise both the thermal and mechanical properties that can lead to die cracking during package and other reliability issues. Boron carbon nitride (BCN) compounds have been expected to combine the excellent properties of boron carbide (B4C), boron nitride (BN) and carbon nitride (C3N4), with their properties adjustable, depending on composition and structure. BCN thin film is a good candidate for being hard, dense, pore-free, low-k dielectric with values in the range of 1.9 to 2.1. Excellent mechanical properties such as adhesion, high hardness and good wear resistance have been reported in the case of sputtered BCN thin films. Problems posed by high hardness materials such as diamonds in high cutting applications and the comparatively lower hardness of c-BN gave rise to the idea of a mixed phase that can overcome these problems with a minimum compromise in its properties. A hybrid between semi-metallic graphite and insulating h-BN may show adjusted semiconductor properties. BCN exhibits the potential to control optical bandgap (band gap engineering) by atomic composition, hence making it a good candidate for electronic and photonic devices. Due to tremendous bandgap engineering capability and refractive index variability in BCN thin film, it is feasible to develop filters and mirrors for use in ultra violet (UV) wavelength region. It is of prime importance to understand process integration challenges like deposition rates, curing, and etching, cleaning and polishing during characterization of low-k films. The sputtering technique provides unique advantages over other techniques such as freedom to choose the substrate material and a uniform deposition over relatively large area. BCN films are prepared by dual target reactive magnetron sputtering from a B4C and BN targets using DC and RF powers respectively. In this work, an investigation of mechanical, optical, chemical, surface and device characterizations is undertaken. These holistic and thorough studies, will provide the insight into the capability of BCN being a hard, chemically inert, low-k, wideband gap material, as a potential leader in semiconductor and optics industry.
Show less - Date Issued
- 2016
- Identifier
- CFE0006378, ucf:51496
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006378
- Title
- Catalytically Enhanced Heterogeneous Combustion of methane.
- Creator
-
Terracciano, Anthony, Orlovskaya, Nina, Vasu Sumathi, Subith, Chow, Louis, Kassab, Alain, University of Central Florida
- Abstract / Description
-
Heterogeneous combustion is an advanced internal combustion technique, which enables heat recuperation within the flame by utilizing a highly porous ceramic media as a regenerator. Heat released within the gas phase convectively transfers to the solid media. This heat within the solid media then travels towards the inlet, enabling reactant preheating. Such heat redistribution enables stable burning of both ultra-lean fuel/air mixtures, forming a more diffuse flame through the combustion...
Show moreHeterogeneous combustion is an advanced internal combustion technique, which enables heat recuperation within the flame by utilizing a highly porous ceramic media as a regenerator. Heat released within the gas phase convectively transfers to the solid media. This heat within the solid media then travels towards the inlet, enabling reactant preheating. Such heat redistribution enables stable burning of both ultra-lean fuel/air mixtures, forming a more diffuse flame through the combustion chamber, and results in reduced pollutant formation. To further enhance heterogeneous combustion, the ceramic media can be coated with catalytically active materials, which facilitates surface based chemical reactions that could occur in parallel with gas phase reactions.Within this work, a flow stabilized heterogeneous combustor was designed and developed consisting of a reactant delivery nozzle, combustion chamber, and external instrumentation. The reactant delivery nozzle enables the combustor to operate on mixtures of air, liquid fuel, and gaseous fuel. Although this combustor has high fuel flexibility, only gaseous methane was used within the presented experiments. Within the reactant delivery nozzle, reactants flow through a tube mixer, and a homogeneous gaseous mixture is delivered to the combustion chamber. ?-alumina (?-Al2O3), magnesia stabilized zirconia (MgO-ZrO2), or silicon carbide (SiC) was used as the material for the porous media. Measurement techniques which were incorporated in the combustor include an array of axially mounted thermocouples, an external microphone, an external CCD camera, and a gas chromatograph with thermal conductivity detector which enable temperature measurements, acoustic spectroscopy, characterization of thermal radiative emissions, and composition analysis of exhaust gasses, respectively. Before evaluation of the various solid media in the combustion chamber the substrates and catalysts were characterized using X-ray diffraction, X-ray fluorescence, scanning electron microscopy and energy dispersive spectroscopy. MgO-ZrO2 porous media was found to outperform both ?-Al2O3 and SiC matrices, as it was established that higher temperatures for a given equivalence ratio were achieved when the flame was contained within a MgO-ZrO2 matrix. This was explained by the presence of oxygen vacancies within the MgO doped ZrO2 fluorite lattice which facilitated catalytic reactions. Several catalyst compositions were evaluated to promote combustion within a MgO-ZrO2 matrix even further.Catalysts such as: Pd enhanced WC, ZrB2, Ce0.80Gd0.20O1.90, LaCoO3, La0.80Ca0.20CoO3, La0.75Sr0.25Fe0.95Ru0.05O3, and La0.75Sr0.25Cr0.95Ru0.05O3; were evaluated under lean fuel/air mixtures. LaCoO3 outperformed all other catalysts, by enabling the highest temperatures within the combustion chamber, followed by Ce0.80Gd0.20O1.90. Both LaCoO3 and Ce0.80Gd0.20O1.90 enabled a flame to exist at ?=0.45(&)#177;0.02, however LaCoO3 caused the flame to be much more stable. Furthermore, it was discovered that the coating of MgO-ZrO2 with LaCoO3 significantly enhanced the total emissive power of the combustion chamber. In this work as acoustic spectroscopy was used to characterize heterogeneous combustion for the first time. It was found that there is a dependence of acoustic emission n the equivalence ratio and flame position regardless of media and catalyst combination. It was also found that when different catalysts were used, the acoustic tones produced during combustion at fixed reactant flow rates were distinct
Show less - Date Issued
- 2016
- Identifier
- CFE0006508, ucf:51364
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006508
- Title
- Method for Derivation and Synthesis of Electromagnetic Environmental Effects Requirement Limits for Achieving System Level Electromagnetic Compatibility.
- Creator
-
Freeman, Larry, Wu, Thomas, Wahid, Parveen, Wei, Lei, Sundaram, Kalpathy, Chow, Louis, University of Central Florida
- Abstract / Description
-
As humans endeavor to build large-scale complex systems, it will necessitate the integration of engineering practices and techniques to allocate many of the design aspects and responsibility across traditional boundaries. Many of today's large-scale complex systems, like commercial aircraft, satellite systems, and even automobiles use parts from all over the world. A recently completed airframe, largest commercial aircraft in the world, took nearly 30 years to build, required over 400...
Show moreAs humans endeavor to build large-scale complex systems, it will necessitate the integration of engineering practices and techniques to allocate many of the design aspects and responsibility across traditional boundaries. Many of today's large-scale complex systems, like commercial aircraft, satellite systems, and even automobiles use parts from all over the world. A recently completed airframe, largest commercial aircraft in the world, took nearly 30 years to build, required over 400 different suppliers from 20 different countries. These kinds of projects dictate a method for derivation and synthesis of electromagnetic environmental effects (E3) requirement limits for achieving system level electromagnetic compatibility (EMC).If a system level EMC design is an assemblage of compliant subsystems, then the subsystems should be an assemblage of compliant module and component designs. This requires tailoring the system level requirements through to module or component level designs. The method discussed is applicable to a variety of designs across varying levels of complexity and importantly implementable early in the design process. The method provides rationale for derivation of limits while maintaining traceability to system level requirements. Specific examples using the four common divisions of EMC requirements, conducted emissions, radiated emissions, conducted susceptibility, and radiated susceptibility are included. An overall system engineering approach and formal methodology is included. Detailed comparison examples using commercial and military EMC requirements are also included. Lastly, a discussion is included on comparison and margin analysis of input filtering for verifying compliance to requirements at the system level.
Show less - Date Issued
- 2016
- Identifier
- CFE0006303, ucf:51603
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006303
- Title
- Design of High-Efficiency Rare-Earth Permanent Magnet Synchronous Motor and Drive System.
- Creator
-
Liu, Hanzhou, Wu, Thomas, Batarseh, Issa, Haralambous, Michael, Lin, Mingjie, Chow, Louis, University of Central Florida
- Abstract / Description
-
Utilization of renewable energy has become the future trend in the trucking industry. Electrical power generated from renewable energy can replace part of the fuel usage. There is usually limited space for storing on-board battery. Thus, to better utilize the battery power, it becomes critical to have an efficient energy conversion device that can transfer energy from battery to amenities such as air conditioner, microwave, TV, mini refrigerator, etc. In this dissertation, a designed...
Show moreUtilization of renewable energy has become the future trend in the trucking industry. Electrical power generated from renewable energy can replace part of the fuel usage. There is usually limited space for storing on-board battery. Thus, to better utilize the battery power, it becomes critical to have an efficient energy conversion device that can transfer energy from battery to amenities such as air conditioner, microwave, TV, mini refrigerator, etc. In this dissertation, a designed permanent magnet synchronous motor (PMSM) can be such energy conversion device for an electric Auxiliary Power Unit (APU) application, which will have a desired output power of 2 kW at 2krpm, and maintain an efficiency greater than 90%. The design calls for good performance over a speed range of 1.5 krpm to 2.5 krpm. The current air conditioning system for automobile works only by (")on(") or (")off(") mode. For the heat mode, that means it is on with heat once the cabin temperature drops down to a level and off if the temperature rises back above that level. For the cool mode, that means it is on with cold air once the cabin temperature rises above a level, and off if the temperature drops back to that level. This is because the motor does not have the speed control functionality according to the temperature variation and people in the cabin do not feel much comfortable for that temperature change periodically as well as the inefficient energy consumption. With our novel technology, the designed motor can adjust its speed through the embedded system of our novel DC to AC inverter to provide a variable load. For example, with high efficiency, the fully charged battery sets (48 volts) can supply the electrical power and cooling to the cabin forabout 10 hours without recharging using the main engine.Copper loss is the most significant part of all the losses in low speed electric machines. Reducing the copper loss is the key to build highly efficient machine. We use copper wires with the current density lower than traditional design which result in large cross section of the wire and thus reduce the copper loss and improve the efficiency. This also makes thermal management easier and reduces the need to use active cooling methodologies (such as fan, liquid cooling or spray cooling); and hence the overall power density of the whole system (including cooling devices) will not decease much. In traditional machine design, the torque angle is designed to be in the rangeof 15 to 30 degrees at the rated power and speed. In our high efficiency motor design, we propose to use much lower torque angle of 2 to 15 degrees at the rated power and speed. Such design caneffectively increase the overload power handling capability and efficiency. Besides, small torque angle will result in large airgap size and increased thickness of the permanent magnets. Large airgap helps to reduce the windage loss of the machine and generates a lot less mechanical noise based on our design experience. Increased thickness of the permanent magnets helps to avoid thedemagnetization.As the technology of advanced micro-controller develops, fast response power electronic devices can be used in the motor controller. A novel design of DC to AC inverter with the fieldoriented control scheme and sliding mode observer algorithm for driving the designed motor is developed. The inverter has the capability of driving the motor with its output power at 2 kW.
Show less - Date Issued
- 2015
- Identifier
- CFE0006224, ucf:51064
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006224
- Title
- Analysis and Design Optimization of Multiphase Converter.
- Creator
-
Zhang, Kejiu, Wu, Xinzhang, Batarseh, Issa, Yuan, Jiann-Shiun, Sundaram, Kalpathy, Chow, Louis, University of Central Florida
- Abstract / Description
-
Future microprocessors pose many challenges to the power conversion techniques. Multiphase synchronous buck converters have been widely used in high current low voltage microprocessor application. Design optimization needs to be carefully carried out with pushing the envelope specification and ever increasing concentration towards power saving features. In this work, attention has been focused on dynamic aspects of multiphase synchronous buck design. The power related issues and optimizations...
Show moreFuture microprocessors pose many challenges to the power conversion techniques. Multiphase synchronous buck converters have been widely used in high current low voltage microprocessor application. Design optimization needs to be carefully carried out with pushing the envelope specification and ever increasing concentration towards power saving features. In this work, attention has been focused on dynamic aspects of multiphase synchronous buck design. The power related issues and optimizations have been comprehensively investigated in this paper. In the first chapter, multiphase DC-DC conversion is presented with background application. Adaptive voltage positioning and various nonlinear control schemes are evaluated. Design optimization are presented to achieve best static efficiency over the entire load range. Power loss analysis from various operation modes and driver IC definition are studied thoroughly to better understand the loss terms and minimize the power loss. Load adaptive control is then proposed together with parametric optimization to achieve optimum efficiency figure.New nonlinear control schemes are proposed to improve the transient response, i.e. load engage and load release responses, of the multiphase VR in low frequency repetitive transient. Drop phase optimization and PWM transition from long tri-state phase are presented to improve the smoothness and robustness of the VR in mode transition. During high frequency repetitive transient, the control loop should be optimized and nonlinear loop should be turned off. Dynamic current sharing are thoroughly studied in chapter 4. The output impedance of the multiphase synchronous buck are derived to assist the analysis. Beat frequency is studied and mitigated by proposing load frequency detection scheme by turning OFF the nonlinear loop and introducing current protection in the control loop.Dynamic voltage scaling (DVS) is now used in modern Multi-Core processor (MCP) and multiprocessor System-on-Chip (MPSoC) to reduce operational voltage under light load condition. With the aggressive motivation to boost dynamic power efficiency, the design specification of voltage transition (dv/dt) for the DVS is pushing the physical limitation of the multiphase converter design and the component stress as well. In this paper, the operation modes and modes transition during dynamic voltage transition are illustrated. Critical dead-times of driver IC design and system dynamics are first studied and then optimized. The excessive stress on the control MOSFET which increases the reliability concern is captured in boost mode operation. Feasible solutions are also proposed and verified by both simulation and experiment results. CdV/dt compensation for removing the AVP effect and novel nonlinear control scheme for smooth transition are proposed for dealing with fast voltage positioning. Optimum phase number control during dynamic voltage transition is also proposed and triggered by voltage identification (VID) delta to further reduce the dynamic loss. The proposed schemes are experimentally verified in a 200 W six phase synchronous buck converter.Finally, the work is concluded. The references are listed.
Show less - Date Issued
- 2013
- Identifier
- CFE0005079, ucf:50742
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005079
- Title
- Development of Thulium Fiber Lasers for High Average Power and High Peak Power Operation.
- Creator
-
Sims, Robert, Richardson, Martin, Schulzgen, Axel, Delfyett, Peter, Chow, Louis, University of Central Florida
- Abstract / Description
-
High power thulium fiber lasers are useful for a number of applications in both continuous-wave and pulsed operating regimes. The use of thulium as a dopant has recently gained interest due to its large bandwidth, possibility of high efficiency, possibility of high power and long wavelength ~1.8 (-) 2.1 ?m. The longer emission wavelength of Tm-doped fiber lasers compared to Yb- and/or Er-doped fiber lasers creates the possibility for higher peak power operation due to the larger nonlinear...
Show moreHigh power thulium fiber lasers are useful for a number of applications in both continuous-wave and pulsed operating regimes. The use of thulium as a dopant has recently gained interest due to its large bandwidth, possibility of high efficiency, possibility of high power and long wavelength ~1.8 (-) 2.1 ?m. The longer emission wavelength of Tm-doped fiber lasers compared to Yb- and/or Er-doped fiber lasers creates the possibility for higher peak power operation due to the larger nonlinear thresholds and reduced nonlinear phase accumulation. One primary interest in Tm-doped fiber lasers has been to scale to high average powers; however, the thermal and mechanical constraints of the fiber limit the average power out of a single-fiber aperture. One method to overcome the constraints of a single laser aperture is to spectrally combine the output from multiple lasers operating with different wavelengths into a single beam. In this thesis, results will be presented on the development of three polarized 100 W level laser systems that were wavelength stabilized for SBC. In addition to the development of the laser channels, the beams were combined using bandpass filters to achieve a single near diffraction-limited output.Concurrently, with the development of high average power systems there is an increasing interest in femotosecond pulse generation and amplification using Tm- doped fiber lasers. High peak power sources operating near 2 (&)#181;m have the potential to be efficient pump sources to generate mid-infrared light through supercontinuum generation or optical parametric oscillators. This thesis focuses on the development of a laser system utilizing chirped pulse amplification (CPA) to achieve record level energies and peak powers for ultrashort pulses in Tm-doped fiber. A mode-locked oscillator was built to generate femtosecond pulses operating with pJ energy. Pulses generated in the mode-locked oscillator were limited to low energies and contained spectral modulation due to the mode-locking mechanism, therefore, a Raman-soliton self-frequency shift (Raman-SSFS) amplifier was built to amplify pulses, decrease the pulse duration, and spectrally clean pulses. These pulses were amplified using chirped pulse amplification (CPA) in which, limiting factors for amplification were examined and a high peak power system was built. The primary limiting factors of CPA in fibers include the nonlinear phase accumulation, primarily through self-phase modulation (SPM), and gain narrowing. Gain narrowing was examined by temporally stretching pulses in a highly nonlinear fiber that both stretched the pulse duration and broadened the spectrum. A high peak power CPA system amplified pulses to 1 (&)#181;J energy with 300 fs compressed pulses, corresponding to a peak power (>)3 MW. High peak power pulses were coupled into highly nonlinear fibers to generate supercontinuum.
Show less - Date Issued
- 2012
- Identifier
- CFE0004752, ucf:49768
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004752
- Title
- Multi-Physics Model of Key Components In High Efficiency Vehicle Drive.
- Creator
-
Lin, Shao Hua, Wu, Xinzhang, Sundaram, Kalpathy, Wahid, Parveen, Wei, Lei, Chow, Louis, University of Central Florida
- Abstract / Description
-
Hybrid Electric Vehicles (HEVs) and Electric Vehicles (EVs) are crucial technologies for the automotive industry to meet society's demands for cleaner, more energy efficient transportation. Meeting the need to provide power which sustains HEVs and EVs is an immediate area of concern that research and development within the automotive community must address. Electric batteries and electrical motors are the key components in HEV and EV power generation and transmission, and their performance...
Show moreHybrid Electric Vehicles (HEVs) and Electric Vehicles (EVs) are crucial technologies for the automotive industry to meet society's demands for cleaner, more energy efficient transportation. Meeting the need to provide power which sustains HEVs and EVs is an immediate area of concern that research and development within the automotive community must address. Electric batteries and electrical motors are the key components in HEV and EV power generation and transmission, and their performance plays very important role in the overall performance of the modern high efficiency vehicles. Therefore, in this dissertation, we are motivated to study the electric batteries, interior permanent motor (IPM), in the context of modern hybrid electric/electric drive systems, from both multi-physics and system level perspectives. Electrical circuit theory, electromagnetic Finite Element Analysis (FEA), and Computational Fluid Dynamic (CFD) finite volume method will be used primarily in this work. The work has total of five parts, and they are introduced in the following.Firstly, Battery thermal management design is critical in HEV and EV development. Accurate temperature distribution of the battery cells during vehicle operation is required for achieving optimized design. We propose a novel electrical-thermal battery modeling technique that couples a temperature dependent battery circuit model and a physics-based CFD model to meet this need. The electrical circuit model serves as a heat generation mechanism for the CFD model, and the CFD model provides the temperature distribution of the battery cells, which can also impact the heat generation of the electrical battery model. In this part of work, simulation data has been derived from the model respective to electrical performance of the battery as well as the temperature distribution simultaneously in consideration of the physical dimensions, material properties, and cooling conditions. The proposed model is validated against a battery model that couples the same electrical model with a known equivalent thermal model.Secondly, we propose an accurate system level Foster network thermal model. The parameters of the model are extracted from step responses of the CFD battery thermal model. The Foster network model and the CFD model give the same results. The Foster network can couple with battery circuit model to form an electric-thermal battery model for system simulation.Thirdly, IPM electric machines are important in high performance drive systems. During normal operations, irreversible demagnetization can occur due to temperature rise and various loading conditions. We investigate the performance of an IPM using 3d time stepping electromagnetic FEA considering magnet's temperature dependency. Torque, flux linkage, induced voltage, inductance and saliency of the IPM will be studied in details. Finally, we use CFD to predict the non-uniform temperature distribution of the IPM machine and the impact of this distribution on motor performance. Fourthly, we will switch gear to investigate the IPM motor on the system level. A reduced order IPM model is proposed to consider the effect of demagnetization of permanent magnet due to temperature effect. The proposed model is validated by comparing its results to the FEA results.Finally, a HEV is a vehicle that has both conventional mechanical (i.e. internal combustion engine) and electrical propulsion systems. The electrical powertrain is used to work with the conventional powertrain to achieve higher fuel economy and lower emissions. Computer based modeling and simulation techniques are therefore essential to help reduce the design cost and optimize system performance. Due to the complexity of hybrid vehicles, multi-domain modeling ability is preferred for both component modeling and system simulation. We present a HEV library developed using VHDL-AMS.
Show less - Date Issued
- 2013
- Identifier
- CFE0005024, ucf:50016
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005024
- Title
- Modeling and Simulation of All-electric Aircraft Power Generation and Actuation.
- Creator
-
Woodburn, David, Wu, Xinzhang, Batarseh, Issa, Georgiopoulos, Michael, Haralambous, Michael, Chow, Louis, University of Central Florida
- Abstract / Description
-
Modern aircraft, military and commercial, rely extensively on hydraulic systems. However, there is great interest in the avionics community to replace hydraulic systems with electric systems. There are physical challenges to replacing hydraulic actuators with electromechanical actuators (EMAs), especially for flight control surface actuation. These include dynamic heat generation and power management.Simulation is seen as a powerful tool in making the transition to all-electric aircraft by...
Show moreModern aircraft, military and commercial, rely extensively on hydraulic systems. However, there is great interest in the avionics community to replace hydraulic systems with electric systems. There are physical challenges to replacing hydraulic actuators with electromechanical actuators (EMAs), especially for flight control surface actuation. These include dynamic heat generation and power management.Simulation is seen as a powerful tool in making the transition to all-electric aircraft by predicting the dynamic heat generated and the power flow in the EMA. Chapter 2 of this dissertation describes the nonlinear, lumped-element, integrated modeling of a permanent magnet (PM) motor used in an EMA. This model is capable of representing transient dynamics of an EMA, mechanically, electrically, and thermally.Inductance is a primary parameter that links the electrical and mechanical domains and, therefore, is of critical importance to the modeling of the whole EMA. In the dynamic mode of operation of an EMA, the inductances are quite nonlinear. Chapter 3 details the careful analysis of the inductances from finite element software and the mathematical modeling of these inductances for use in the overall EMA model.Chapter 4 covers the design and verification of a nonlinear, transient simulation model of a two-step synchronous generator with three-phase rectifiers. Simulation results are shown.
Show less - Date Issued
- 2013
- Identifier
- CFE0005074, ucf:49975
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005074
- Title
- Agglomeration, Evaporation and Morphological Changes in Droplets with Nanosilica and Nanoalumina Suspensions in an Acoustic Field.
- Creator
-
Tijerino Campollo, Erick, Kumar, Ranganathan, Deng, Weiwei, Chow, Louis, Basu, Saptarshi, University of Central Florida
- Abstract / Description
-
Acoustic levitation permits the study of droplet dynamics without the effects of surface interactions present in other techniques such as pendant droplet methods. Despite the complexities of the interactions of the acoustic field with the suspended droplet, acoustic levitation provides distinct advantages of controlling morphology of droplets with nanosuspensions post precipitation. Droplet morphology is controlled by vaporization, deformation and agglomeration of nanoparticles, and therefore...
Show moreAcoustic levitation permits the study of droplet dynamics without the effects of surface interactions present in other techniques such as pendant droplet methods. Despite the complexities of the interactions of the acoustic field with the suspended droplet, acoustic levitation provides distinct advantages of controlling morphology of droplets with nanosuspensions post precipitation. Droplet morphology is controlled by vaporization, deformation and agglomeration of nanoparticles, and therefore their respective timescales are important to control the final shape. The balance of forces acting on the droplet, such as the acoustic pressure and surface tension, determine the geometry of the levitated droplet. Thus, the morphology of the resultant structure can be controlled by manipulating the amplitude of the levitator and the fluid properties of the precursor nanosuspensions. The interface area in colloidal nanosuspensions is very large even at low particle concentrations. The effects of the presence of this interface have large influence in the properties of the solution even at low concentrations.This thesis focuses on the dynamics of particle agglomeration in acoustically levitated evaporating nanofluid droplets leading to shell structure formation. These experiments were performed by suspending 500(&)#181;m droplets in a pressure node of a standing acoustic wave in a levitator and heating them using a carbon dioxide laser. These radiatively heated functional droplets exhibit three distinct stages, namely, pure evaporation, agglomeration and structure formation. The temporal history of the droplet surface temperature shows two inflection points. Morphology and final precipitation structures of levitated droplets are due to competing mechanisms of particle agglomeration, evaporation and shape deformation. This thesis provides a detailed analysis for each process and proposes two important timescales for evaporation and agglomeration that determine the final diameter of the structure formed. It is seen that both agglomeration and evaporation timescales are similar functions of acoustic amplitude (sound pressure level), droplet size, viscosity and density. However it is shown that while the agglomeration timescale decreases with initial particle concentration, the evaporation timescale shows the opposite trend. The final normalized diameter hence can be shown to be dependent solely on the ratio of agglomeration to evaporation timescales for all concentrations and acoustic amplitudes. The experiments were conducted with 10nm silica, 20nm silica, 20nm alumina and 50nm alumina solutions. The structures exhibit various aspect ratios (bowls, rings, spheroids) which depend on the ratio of the deformation timescale (tdef) and the agglomeration timescale (tg).
Show less - Date Issued
- 2012
- Identifier
- CFE0004610, ucf:49914
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004610
- Title
- Three-phase contact line phenomena in droplets on solid and liquid surfaces: electrocapillary, pinning, wetting line velocity effect, and free liquid surface deformation.
- Creator
-
Shabani, Roxana, Cho, Hyoung, Kumar, Ranganathan, Kapat, Jayanta, Chow, Louis, Zhai, Lei, University of Central Florida
- Abstract / Description
-
In this dissertation, physical phenomena relevant to (i) an interface formed between two fluids and a solid phase (wettingline) and (ii) an interface between three fluids (triple contact line) were investigated. In the former case, the wetting line (WL)phenomena, which encompass the wetting line energy (WLE), the wetting line velocity (WLV), and the contact anglehysteresis, were studied using a micropump based on electrowetting on dielectric (EWOD). In the latter case, the air filmlubrication...
Show moreIn this dissertation, physical phenomena relevant to (i) an interface formed between two fluids and a solid phase (wettingline) and (ii) an interface between three fluids (triple contact line) were investigated. In the former case, the wetting line (WL)phenomena, which encompass the wetting line energy (WLE), the wetting line velocity (WLV), and the contact anglehysteresis, were studied using a micropump based on electrowetting on dielectric (EWOD). In the latter case, the air filmlubrication effect and the liquid free surface deformation were taken into account to explain the dual equilibrium states ofwater droplets on liquid free surfaces. A micropump based on droplet/meniscus pressure gradient generated by EWOD was designed and fabricated. By alteringthe contact angle between liquid and solid using an electric field a pressure gradient was induced and a small droplet waspumped into the channel. The flow rate in the channel was found to be constant in spite of the changes in the droplet'sradius. The WL phenomena were studied to unravel the physical concept behind the micropump constant flow rate. Theobservation and measurement reveal that the shrinking input droplet changes its shape in two modes in time sequence: (i)its contact angle decreases, while its wetting area remains constant, and (ii) its WL starts to move while its contact anglechanges. Contact angles were measured for the advancing and receding WLs at different velocities to capture a full pictureof contact angle behavior. The effects of the WLE on the static contact angle and the WLV on the dynamic contact angle inthe pump operation were investigated. Also the effect of EWOD voltage on the magnitude and uniformity of the micropumpflow rate was studied. Dynamic contact angles were used to accurately calculate the pressure gradient between the dropletand the meniscus, and estimate the flow rate. It was shown that neglecting either of these effects not only results in aconsiderable gap between the predicted and the measured flow rates but also in an unphysical instability in the flow rateanalysis. However, when the WLE and WLV effects were fully taken into account, an excellent agreement between thepredicted and the experimental flow rates was obtained.For the study of the TCL between three fluids, aqueous droplets were formed at oil-air interface and two stableconfigurations of (i) non-coalescent droplet and (ii) cap/bead droplet were observed. General solutions for energy and forceanalysis were obtained and were shown to be in good agreement with the experimental observations. Further the energybarrier obtained for transition from configuration (i) to (ii) was correlated to the droplet release height and the probability ofnon-coalescent droplet formation. Droplets formed on the solid surfaces and on the free surface of immiscible liquids have various applications indroplet-based microfluidic devices. This research provides an insight into their formation and manipulation.
Show less - Date Issued
- 2013
- Identifier
- CFE0005253, ucf:50598
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005253
- Title
- DESIGN AND DEVELOPMENT OF HETEROGENOUS COMBUSTION SYSTEMS FOR LEAN BURN APPLICATIONS.
- Creator
-
Terracciano, Anthony, Orlovskaya, Nina, Vasu Sumathi, Subith, Chow, Louis, Kassab, Alain, University of Central Florida
- Abstract / Description
-
Combustion with a high surface area continuous solid immersed within the flame, referred to as combustion in porous media, is an innovative approach to combustion as the solid within the flame acts as an internal regenerator distributing heat from the combustion byproducts to the upstream reactants. By including the solid structure, radiative energy extraction becomes viable, while the solid enables a vast extension of flammability limits compared to conventional flames, while offering...
Show moreCombustion with a high surface area continuous solid immersed within the flame, referred to as combustion in porous media, is an innovative approach to combustion as the solid within the flame acts as an internal regenerator distributing heat from the combustion byproducts to the upstream reactants. By including the solid structure, radiative energy extraction becomes viable, while the solid enables a vast extension of flammability limits compared to conventional flames, while offering dramatically reduced emissions of NOx and CO, and dramatically increased burning velocities. Efforts documented within are used for the development of a streamlined set of design principles, and characterization of the flame's behavior when operating under such conditions, to aid in the development of future combustors for lean burn applications in open flow systems. Principles described herein were developed from a combination of experimental work and reactor network modeling using CHEMKIN-PRO. Experimental work consisted of a parametric analysis of operating conditions pertaining to reactant flow, combustion chamber geometric considerations and the viability of liquid fuel applications. Experimental behavior observed, when utilizing gaseous fuels, was then used to validate model outputs through comparing thermal outputs of both systems. Specific details pertaining to a streamlined chemical mechanism to be used in simulations, included within the appendix, and characterization of surface area of the porous solid are also discussed. Beyond modeling the experimental system, considerations are also undertaken to examine the applicability of exhaust gas recirculation and staged combustion as a means of controlling the thermal and environmental output of porous combustion systems. This work was supported by ACS PRF #51768-ND10 and NSF IIP 1343454.
Show less - Date Issued
- 2014
- Identifier
- CFE0005269, ucf:50549
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005269
