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Title: EFFECTS OF BINARY SOLVENT SYSTEM ON MORPHOLOGY OF PARTICLES.
Creator: Besana, Patrick, Deng, Weiwei, University of Central Florida
Abstract / Description: Recent advancements in cancer research has led to the synthesis of a new drug known as docetaxel. Meant to replace paclitaxel, its more natural counterpart whose ingredients are difficult to obtain, the drug is known to effectively treat a wide array of cancers, including breast cancer, ovarian cancer, and prostate cancer. The establishment of a synthetic alternative to paclitaxel has increased its bioavailability, thereby lowering the cost needed to utilize the drug. Still, the limiting...
Show moreRecent advancements in cancer research has led to the synthesis of a new drug known as docetaxel. Meant to replace paclitaxel, its more natural counterpart whose ingredients are difficult to obtain, the drug is known to effectively treat a wide array of cancers, including breast cancer, ovarian cancer, and prostate cancer. The establishment of a synthetic alternative to paclitaxel has increased its bioavailability, thereby lowering the cost needed to utilize the drug. Still, the limiting factor in minimizing costs is the method in which the drug is processed. Current methods in drug processing have their limitations, which include the introduction of impurities and a low effective yield due to poor powder geometry. Thus, the goal of this study looks to explore a new way to process the drug in a more efficient manner. In this study, a new method for processing docetaxel is explored on in great detail. A more direct method of using electrospray deposition is utilized for the creation of monodisperse nanoparticles, with the main intention of increasing the efficiency at which the drug is processed and prepared for drug delivery to the patient by means of injection. A key feature in electrospray deposition is its ability to produce droplets that are sized homogenously. These droplets eventually evaporate at homogenous rates. These two concepts have been exploited to consistently produce nanoparticles of the cancer drug, which is made possible by the fact that the minimal variation in droplet sizes has easily translated to minimal variation in dry particle sizes. Compared to other methods of drug processing, one other benefit that electrospray deposition conveys is that through evaporation, virtually all impurities and unwanted foreign material are eliminated. Moreover, a binary solvent system is investigated in more detail in this study, so as to determine its effects on both the evaporation of the solvent and the diffusion of the drug into nanoparticles. From there, material and geometric properties of the electrospray nozzle were explored upon in great detail, with the main goal of being able to produce a cone jet that consistently dissociates into monodisperse droplets. At the same time, controllable properties of the electrospray atomizer were investigated and continuously modified. Modifications in both the components of the solution and the operating temperature were also considered to enhance both the electrospray deposition process and the geometry of the particles. Scanning electron microscopy (SEM) characterization is continuously utilized to determine suitability of results obtained in experiments. Ultimately, the goal of this study is to determine the ideal conditions (solvent ratios, flow rate, operating temperature, electrospray atomizer nozzle configurations, etc.) in which spherical docetaxel particles sized at 100-200 nm can be produced.
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Date Issued: 2015
Identifier: CFH0004872, ucf:45412
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004872

Title: MICROSCOPIC SURFACE TEXTURES CREATED BY INTERFACIAL FLOW INSTABILITIES.
Creator: Gu, Jing, Weiwei Deng, Dr., University of Central Florida
Abstract / Description: In nature, microscopic surface textures impact useful function, such as the drag reduction of shark skin (Dean & Bhushan, 2010) and superhydrophobicity of the lotus leaf(Pan, Kota, Mabry, & Tuteja, 2013). In this study, we explore these phenomena by re-creating microscopic surface textures via the method of interfacial flow instability in drying polyvinylidene fluoride (PVDF) acetone solutions. In general, PVDF films can be made using either spin coating or electrospray deposition with...
Show moreIn nature, microscopic surface textures impact useful function, such as the drag reduction of shark skin (Dean & Bhushan, 2010) and superhydrophobicity of the lotus leaf(Pan, Kota, Mabry, & Tuteja, 2013). In this study, we explore these phenomena by re-creating microscopic surface textures via the method of interfacial flow instability in drying polyvinylidene fluoride (PVDF) acetone solutions. In general, PVDF films can be made using either spin coating or electrospray deposition with various weight concentrations in acetone. In order to study the morphology of the porous structure of PVDF films, wet deposition samples were fabricated by spin coating or near-field electrospray. Possible theories are discussed and examined to explain the formation of these porous structures resulting in development of a well-controlled method to create porous PVDF films with various pore sizes and pore densities. All samples are characterized and found to exhibit superhydrophobicity and drag reduction. To connect porous PVDF film morphology to the established field of dry particle fabrication, PVDF particle synthesis by far-field electrospray is also reviewed and discussed. An established method to generate polymer particles of different morphologies in other polymers (Almeria-Diez, 2012) by electrospray drying is confirmed using PVDF as well. Due to the ability of scalable and re-configurable electrospray, the microscopic surface textures can be applied to areas of any size to reduce drag or impart water-repelling properties.
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Date Issued: 2013
Identifier: CFH0004479, ucf:45066
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004479

Title: Towards Scalable Nanomanufacturing: Modeling the Interaction of Charged Droplets from Electrospray using GPU.
Creator: Yang, Weiwei, Deng, Weiwei, Chen, Ruey-Hung, Ilie, Marcel, University of Central Florida
Abstract / Description: Electrospray is an atomization method subject to intense study recently due to its monodispersity and the wide size range of droplets it can produce, from nanometers to hundreds of micrometers. This thesis focuses on the numerical and theoretical modeling of the interaction of charged droplets from the single and multiplexed electrospray. We studied two typical scenarios: large area film depositions using multiplexed electrospray and fine pattern printings assisted by linear electrostatic...
Show moreElectrospray is an atomization method subject to intense study recently due to its monodispersity and the wide size range of droplets it can produce, from nanometers to hundreds of micrometers. This thesis focuses on the numerical and theoretical modeling of the interaction of charged droplets from the single and multiplexed electrospray. We studied two typical scenarios: large area film depositions using multiplexed electrospray and fine pattern printings assisted by linear electrostatic quadrupole focusing. Due to the high computation power requirement in the unsteady n-body problem, graphical processing unit (GPU) which delivers 10 Tera flops in computation power is used to dramatically speed up the numerical simulation both efficiently and with low cost. For large area film deposition, both the spray profile and deposition number density are studied for different arrangements of electrospray and electrodes. Multiplexed electrospray with hexagonal nozzle configuration can not give us uniform deposition though it has the highest packing density. Uniform film deposition with variation (<) 5% in thickness was observed with the linear nozzle configuration combined with relative motion between ES source and deposition substrate. For fine pattern printing, linear quadrupole is used to focus the droplets in the radial direction while maintaining a constant driving field at the axial direction. Simulation shows that the linear quadrupole can focus the droplets to a resolution of a few nanometers quickly when the inter-droplet separation is larger than a certain value. Resolution began to deteriorate drastically when the inter-droplet separation is smaller than that value. This study will shed light on using electrospray as a scalable nanomanufacturing approach.
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Date Issued: 2012
Identifier: CFE0004463, ucf:49333
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004463

Title: Response of Electrified Micro-Jets to Electrohydrodynamic Perturbations.
Creator: Yang, Weiwei, Deng, Weiwei, Chen, Ruey-Hung, Ilie, Marcel, University of Central Florida
Abstract / Description: The breakup of liquid jets is ubiquitous with rich underpinning physics and widespread applications. The natural breakup of liquid jets originates from small ambient perturbations, which can grow exponentially until the amplitude as large as the jet radius is reached. For unelectrified inviscid jets, surface energy analysis shows that only the axisymmetric perturbation is possibly unstable, and this mode is referred as varicose instability. For electrified jets, the presence of surface charge...
Show moreThe breakup of liquid jets is ubiquitous with rich underpinning physics and widespread applications. The natural breakup of liquid jets originates from small ambient perturbations, which can grow exponentially until the amplitude as large as the jet radius is reached. For unelectrified inviscid jets, surface energy analysis shows that only the axisymmetric perturbation is possibly unstable, and this mode is referred as varicose instability. For electrified jets, the presence of surface charge enables additional unstable modes, among which the most common one is the whipping (or kink) instability that bends and stretches the charged jet that is responsible for the phenomena of electrospinning. A closer examination of the two instabilities suggests that due to mass conservation, the uneven jet stretching from whipping may translate into radial perturbations and trigger varicose instabilities. Although the varicose and whipping instabilities of electrified micro-jets have both been extensively studied separately, there is little attention paid to the combined effect of these two, which may lead to new jet breakup phenomena. This dissertation investigates the dynamic response of electrified jets under transverse electrohydrodynamic (EHD) perturbations which were introduced by exciters driven by alternating voltage of sweeping frequency. Three different jetting mechanisms are used to generate jets with various ranges of jet diameters: ~150 micrometer inertial jets from liquid pressurized through a small orifice, ~50 micrometer flow focused jets, and ~20 micrometer electrified Taylor-cone jets. The transverse perturbations enable systematic triggering of varicose and whipping instabilities, and consequently a wide range of remarkable phenomena emerge. For inertial jets with zero or low charge levels, only varicose instability is observable due to suppressed whipping instability. At modest charge levels, inertia jets can respond to the fundamental perturbation frequency as well as the second harmonic of the perturbation frequency. Highly charged jets such as fine jets generated from Taylor cones exhibit distinct behavior for different perturbation wavenumber x. Typical behavior include: whipping jets with superimposed varicose instability at small x, jet bifurcation from crossover of whipping and varicose instabilities at x~0.5, Coulombic fission owing to the surge of surface charge density as the slender liquid segments recover spherical shapes at x~0.7, and simple varicose mode near wave numbers of unity. The phenomena observed in this work may be explained by a linear model and rationalized by the phase diagram in the space of wave number and dimensionless charge levels. The experimental apparatus used in this dissertation is simple, non-intrusive, and scalable to a linear array of jets. The rich phenomena combined with the versatile apparatus may spawn new research directions such as regulated electrospinning, generating strictly monodisperse micro/nano droplets, and manufacturing of non-spherical particles from drying droplets that undergo controlled Coulombic fissions.
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Date Issued: 2014
Identifier: CFE0005744, ucf:50086
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005744

Title: Purge and Secondary Flow Interaction Control by Means of Platform Circumferential Contouring.
Creator: Seco Soley, Melissa, Kapat, Jayanta, Deng, Weiwei, Gordon, Ali, University of Central Florida
Abstract / Description: This study presents an attempt to reduce the losses produced by the purge flow in a turbine stage by incorporating circumferential platform contouring. Two contours are proposed and compared against a baseline at different levels of swirl. The computational simulations were performed using a RANS three-dimensional Computational Fluid Dynamics code with the Shear Stress Transport turbulence model. The results of steady simulations demonstrate that for the first contour, when the flow is...
Show moreThis study presents an attempt to reduce the losses produced by the purge flow in a turbine stage by incorporating circumferential platform contouring. Two contours are proposed and compared against a baseline at different levels of swirl. The computational simulations were performed using a RANS three-dimensional Computational Fluid Dynamics code with the Shear Stress Transport turbulence model. The results of steady simulations demonstrate that for the first contour, when the flow is swirled to 50% of the rim speed, the purge flow exits the cavity with less cross flow. This in turn reduces the strength of the passage vortex. However, at swirl extremes of 0% and 100% the baseline has the best performance. The results show that a carefully designed platform has the potential to reduce losses when the operating condition is in the proximity of 50% swirl.
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Date Issued: 2011
Identifier: CFE0004163, ucf:49054
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004163

Title: An experimental investigation on the dynamics of bubbles utilizing refrigerant R134a under pressurized flow boiling conditions.
Creator: Vereen, Keon, Kumar, Ranganathan, Chow, Louis, Deng, Weiwei, University of Central Florida
Abstract / Description: Flow boiling heat transfer allows for the dissipation of large amounts of heat. In this work, the effect of heat flux and pressure on flow boiling of liquid refrigerant R-134a is studied in a vertical thin channel. The experimental setup mimics a refrigeration cycle and specifically looks at the effect of pressure and wall heat flux on the departure size and bubble generation rate. The experimental setup consists of a closed loop which includes a vertical narrow rectangular channel and two...
Show moreFlow boiling heat transfer allows for the dissipation of large amounts of heat. In this work, the effect of heat flux and pressure on flow boiling of liquid refrigerant R-134a is studied in a vertical thin channel. The experimental setup mimics a refrigeration cycle and specifically looks at the effect of pressure and wall heat flux on the departure size and bubble generation rate. The experimental setup consists of a closed loop which includes a vertical narrow rectangular channel and two synchronized high speed cameras for optical measurements at either sides of the channel. The setup is built to employ an accurate measurement technique to define wall temperatures of the representative flow boiling process. Instead of using thermocouples on the surface channel, the thermochromic liquid crystallography (TLC) technique is used to determine non-invasively the heater surface temperature at high temporal and spatial resolution. The TLC interval range is 30-50(&)deg;C. The TLC is attached to a Fecralloy heating section. The high speed Prosilica cameras simultaneously capture, colored TLC images as well as bubble nucleation and departure at very high frame rates. Experiments on subcooled flow boiling heat transfer have been conducted with refrigerant R-134a under a mass flux range of 484.838 kg/m2s to 1212.1 kg/m2s. With the low mass flux, the wall heat flux ranged from 167.2 to 672.1 kW/m2, the inlet subcooling ranged from 0.35(&)deg;C to 16.55 (&)deg;C, the system pressure ranged from 621 kPa to 1034 kPa. At high mass flux, the wall heat flux ranged from 329.8 kW/m2 to 744 kW/m2, the inlet subcooling from 0.16(&)deg;C to 17.21 (&)deg;C, and the system pressure from 621 kPa to 1034 kPa. A parametric study was done by maintaining various input parameters constant.From the high speed images, bubble parameters such as size and frequency are calculated. Temperature contours are utilized to determine the surface wall temperature at specific points. Sequential wall temperatures are traced over a short period of time to understand the cooling effects. The bubble propagation and coalescence are also visualized. Results show that bubble size and frequency increased with heat flux at any particular pressure. At higher pressure, the trend would be for the bubble size to decrease; however, the inlet subcooling and heat flux also affect bubble size. The bubble frequency is also seen to be affected by the inlet subcooling and the heat flux. Even though the inlet subcooling is maintained approximately constant, any slight decrease in subcooling increased bubble growth rate. Another trend that is observed is that at higher the heat flux, the bubble generation frequency is faster; however no specific trend is observed for wall superheat. With an increase in heat flux, the wall superheats are expected to increase; however, the localized nature of the nucleation activity sites is seen to affect the results. The variables are non-dimensionalized to note trends in parameters. In summary, the data analysis demonstrates that both heat flux and pressure significantly influence the bubble generation rate, size, propagation and coalescence.
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Date Issued: 2011
Identifier: CFE0004175, ucf:49077
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004175

Title: Heat Transfer in a Coupled Impingement-Effusion Cooling System.
Creator: Miller, Mark, Kapat, Jayanta, Deng, Weiwei, Gordon, Ali, University of Central Florida
Abstract / Description: The efficiency of air-breathing gas turbine engines improves as the combustion temperature increases. Therefore, modern gas turbines operate at temperatures greater than the melting temperature of hot-gas-path components, and cooling must be introduced in order to maintain mechanical integrity of those components. Two highly effective techniques used in modern designs for this purpose are impingement cooling and use of coolant film on hot-gas-path surface introduced through discrete film or...
Show moreThe efficiency of air-breathing gas turbine engines improves as the combustion temperature increases. Therefore, modern gas turbines operate at temperatures greater than the melting temperature of hot-gas-path components, and cooling must be introduced in order to maintain mechanical integrity of those components. Two highly effective techniques used in modern designs for this purpose are impingement cooling and use of coolant film on hot-gas-path surface introduced through discrete film or effusion holes. In this study, these two mechanisms are coupled into a single prototype cooling system. The heat transfer capability of this system is experimentally determined for a variety of different geometries and coolant flow rates.This study utilizes Temperature Sensitive Paint (TSP) in order to measure temperature distribution over a surface, which allowed for local impingement Nusselt number, film cooling effectiveness, and film cooling heat transfer enhancement profiles to be obtained. In addition to providing quantitative heat transfer data, this method allowed for qualitative investigation of the flow behavior near the test surface. Impinging jet-to-target-plate spacing was varied over a large range, including several tall impingement scenarios outside the published limits. Additionally, both in-line and staggered effusion arrangements were studied, and results for normal injection were compared to full coverage film cooling with inclined- and compound-angle injection. Effects of impingement and effusion cooling were combined to determine the overall cooling effectiveness of the system.It is shown that low impingement heights produce the highest Nusselt number, and that large jet-to-jet spacing reduces coolant flow rate while maintaining moderate to high heat transfer rates. Staggered effusion configurations exhibit superior performance to in-line configurations, as jet interference is reduced and surface area coverage is improved. Coolant to mainstream flow mass flux ratios greater than unity result in jet blow-off and reduced effectiveness. The convective heat transfer coefficient on the film cooled surface is higher than a similar surface without coolant injection due to the generation of turbulence associated with jet-cross flow interaction.
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Date Issued: 2011
Identifier: CFE0004140, ucf:49042
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004140

Title: Aerodynamic Characteristics of a Gas Turbine Exhaust Diffuser with an Accompanying Exhaust Collection System.
Creator: Bernier, Bryan, Kapat, Jayanta, Deng, Weiwei, Raghavan, Seetha, University of Central Florida
Abstract / Description: The effects of an industrial gas turbine's Exhaust Collector Box (ECB) geometry on static pressure recovery and total pressure loss were investigated in this study experimentally and computationally. This study aims to further understand how exit boundary conditions affect the performance of a diffuser system as well as the accuracy of industry standard computational models. A design of experiments approach was taken using a Box-Behnken design method for investigating three geometric...
Show moreThe effects of an industrial gas turbine's Exhaust Collector Box (ECB) geometry on static pressure recovery and total pressure loss were investigated in this study experimentally and computationally. This study aims to further understand how exit boundary conditions affect the performance of a diffuser system as well as the accuracy of industry standard computational models. A design of experiments approach was taken using a Box-Behnken design method for investigating three geometric parameters of the ECB. In this investigation, the exhaust diffuser remained constant through each test, with only the ECB being varied. A system performance analysis was conducted for each geometry using the total pressure loss and static pressure recovery from the diffuser inlet to the ECB exit. Velocity and total pressure profiles obtained with a hotwire anemometer and Kiel probe at the exit of the diffuser and at the exit of the ECB are also presented in this study. A total of 13 different ECB geometries are investigated at a Reynolds number of 60,000. Results obtained from these experimental tests are used to investigate the accuracy of a 3-dimensional RANS with realizable k-? turbulence model from the commercial software package Star-CCM+. The study confirms the existence of strong counter-rotating helical vortices within the ECB which significantly affect the flow within the diffuser. Evidence of a strong recirculation zone within the ECB was found to force separation within the exhaust diffuser which imposed a circumferentially asymmetric pressure field at the inlet of the diffuser. Increasing the ECB width proved to decrease the magnitude of this effect, increasing the diffuser protrusion reduced this effect to a lesser degree. The combined effect of increasing the ECB Length and Width increased the expansion area ratio, proving to increase the system pressure recovery by as much as 19% over the nominal case. Additionally, the realizable k-? turbulence model was able to accurately rank all 13 cases in order by performance; however the predicted magnitudes of the pressure recovery and total pressure loss were poor for the cases with strong vortices. For the large volume cases with weak vortices, the CFD was able to accurately represent the total pressure loss of the system within 5%.
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Date Issued: 2012
Identifier: CFE0004517, ucf:49296
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004517

Title: Heat Transfer and Friction Augmentation in a Narrow Rectangular Duct with Symmetrical and Non-Symmetrical Wedge-Shaped Turbulators.
Creator: Valentino, Michelle, Kapat, Jayanta, Deng, Weiwei, Kassab, Alain, University of Central Florida
Abstract / Description: The need for cleaner and more fuel efficient means to produce electricity is growing steadily. Advancements in cooling technologies contribute to the improvements in turbine efficiency and are used for gas turbines and for power generation in automotive, aviation, as well as in naval applications, and many more. Studies introducing turbulators on walls of internal cooling channels, which can be applied to hot gas components and in recuperative heat exchangers, have been reviewed for their...
Show moreThe need for cleaner and more fuel efficient means to produce electricity is growing steadily. Advancements in cooling technologies contribute to the improvements in turbine efficiency and are used for gas turbines and for power generation in automotive, aviation, as well as in naval applications, and many more. Studies introducing turbulators on walls of internal cooling channels, which can be applied to hot gas components and in recuperative heat exchangers, have been reviewed for their ability to promote heat transfer in the channel while observing pressure loss caused by adding the features. Several types of turbulators have been studied; ribs, pin fins, dimples, wedges, and scales are some examples of features that have been added to walls of internal cooling channels or heat exchangers to increase heat transfer. This study focuses on two types of wedge turbulator designs, a full symmetrical wedge and a half, or non-symmetrical right-triangular wedge for the purpose of disrupting the thermal boundary layer close to hot walls without causing large-scale mixing and pressure drops. There are two sizes of the wedges, the first set of full and half wedges have an e/Dh=0.10 with the second at e/Dh=0.40, a feature that fills the height of the boundary layer. There are six cases studied, two one-wall and four two-wall cases in a 2:1 aspect ratio channel at Reynolds numbers of 10,000, 20,000, 30,000, and 40,000. Two experimental setups are utilized: a segmented copper block and transient TLC, along with numerical simulation for computational flow visualization. Wall temperature data is collected from all four walls for the copper experimental setup and three walls on the transient TLC setup. The fourth wall of the acrylic test section for the transient TLC tests is utilized for pressure testing, where static pressure ports are placed along the side wall. Although the small features did not show large influence in heat transfer on the side walls as much as the larger features or as high of heat transfer on the featured walls, the minimal pressure loss in the channel kept overall thermal performance of the small two wall full wedge features very high. The case of the large half wedge on two walls also showed very high thermal performance, having pressure loss values nearly half of the same sized (length and height) full wedge feature while having the ability to incorporate side walls into the overall heat transfer enhancement. The results found in the experimental setups are supported by the visualization of flow characteristics from the numerical testing. Comparing the initial wedge study to recent full rib studies show the wedges have similar improvements in heat transfer to the full rib cases with friction augmentations 5 to 10 times lower than the full rib cases. Further improvements to wedge heat transfer and pressure drop can be done by determining optimal wedge size and orientation.
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Date Issued: 2011
Identifier: CFE0004489, ucf:49299
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004489

Title: Imaging long-range orientational order in monolayers of amphiphilic molecules with scanning probe force microscope and liquid crystal optical amplification.
Creator: Liang, Wenlang, Fang, Jiyu, Deng, Weiwei, An, Linan, Huo, Qun, University of Central Florida
Abstract / Description: Monolayers of amphiphilic molecules at interface provide a unique system for understanding the thermodynamic and rheological properties of quasi two-dimensional systems. They are also an excellent model accessible for studying cell membranes. The feature of long-range organization of molecular tilt azimuth in monolayers at the air/water interface is one of the most interesting findings over the past two decades, which leads to the formation rich and defined textures. By observing the changes...
Show moreMonolayers of amphiphilic molecules at interface provide a unique system for understanding the thermodynamic and rheological properties of quasi two-dimensional systems. They are also an excellent model accessible for studying cell membranes. The feature of long-range organization of molecular tilt azimuth in monolayers at the air/water interface is one of the most interesting findings over the past two decades, which leads to the formation rich and defined textures. By observing the changes in these textures, the transitions between tilted monolayer phases can be detected. We study the boojum and stripe textures formed in the liquid-condensed phase of pentadecanoic acid (PDA) monolayers at the air/water interface and find that they can be preserved after being transferred to glass substrates at low dipping speeds at a temperature lower than the room temperature. Frictional force microscopy confirms the long-range tilt order in the transferred boojums and stripes of PDA, implying the interaction of the PDA molecules with the glass surface does not change the tilt order. Polymerized stripe textures of pentacosadiynoic acid (PCA) monolayers can also be transferred onto solid substrates. Atomic force microscopy shows that the PCA stripe textures represent the regular variations of molecular packing densities in PCA monolayers. Furthermore, we find that the molecular orientation and packing density changes in monolayers can induce the local order of nematic liquid crystals. Due to the long-range orientation correlation of nematic liquid crystals, the boojum and stripe textures in monolayers can be observed by an optical microscope after liquid crystal optical amplification.
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Date Issued: 2011
Identifier: CFE0004498, ucf:49294
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004498

Title: Enhanced Structure and Crystallinity of Semiconducting Polymer Films Through Electrospray Deposition.
Creator: Rodriguez, Johan, Deng, Weiwei, Challapalli, Suryanarayana, Orlovskaya, Nina, University of Central Florida
Abstract / Description: Electrospray atomization is a method that uses electrical stresses as the means of generatingcharged droplets. The fundamental working principles of electrospray have previously been extensivelystudied and demonstrated to have monodisperse droplet size distribution, good stabilityand scalability. Electrospray is a bottom-up deposition method which opens up the possibility of aroll-to-roll compatible process and is functional at regular atmospheric conditions. Due to this setof positive...
Show moreElectrospray atomization is a method that uses electrical stresses as the means of generatingcharged droplets. The fundamental working principles of electrospray have previously been extensivelystudied and demonstrated to have monodisperse droplet size distribution, good stabilityand scalability. Electrospray is a bottom-up deposition method which opens up the possibility of aroll-to-roll compatible process and is functional at regular atmospheric conditions. Due to this setof positive qualities, this atomization method holds promise as a means of solution based materialprocessing that is cost effective and scalable. Conjugated polymers are among the solution processablematerials of most interest, poly(3-hexylthiophene)(P3HT) standing out as one of the mostextensively studied. Applications of P3HT as a p-type semiconductor have been demonstrated indevices like organic solar cells, light emitting diodes and transistors. Improvements in the performanceof the mentioned devices have been correlated with a higher degree of crystallinity as wellas the film structure in the case of organic solar cells.The effects of different electrospray process parameters are investigated and various P3HT filmstructures are presented in this study. Electric repulsion present within the droplets in electrosprayand evaporation of the solvent were used to obtain high aspect ratio features on the P3HT films. Aclever design for the electrospray nozzle devised to improve the process stability is presented. Also,the crystallinity of the films was characterized using grazing incidence x-ray diffraction (GIXRD)and ultraviolet visible spectroscopy. All results in this study are presented as a comparison tospin coated control process. The GIXRD results suggest that the electrospray process producescrystallites that have an orientation opposite of the orientation observed in the spin coated process.Analysis of the ultraviolet visible spectroscopy absorption spectrum shows a red-shift, signalingan increase in the crystallinity. Lastly, good contact between the deposited P3HT and the substratewas confirmed using conductive atomic force microscopy (CAFM).iii
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Date Issued: 2015
Identifier: CFE0005879, ucf:50881
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005879

Title: Evaporative Vapor Deposition for Depositing 2D Materials.
Creator: Gleason, Kevin, Putnam, Shawn, Zhai, Lei, Deng, Weiwei, University of Central Florida
Abstract / Description: The development of a new deposition technique called evaporative vapor deposition (EVD) is reported, allowing deposition and formation of atomically-thin, large area materials on arbitrary substrates. This work focuses on the highly popular monolayer material (-) graphene oxide (GO). A droplet of a GO solution is formed on a heated polymer substrate, and maintained at steady-state evaporation (all droplet parameters are held constant over time). The polymer substrate is laser patterned to...
Show moreThe development of a new deposition technique called evaporative vapor deposition (EVD) is reported, allowing deposition and formation of atomically-thin, large area materials on arbitrary substrates. This work focuses on the highly popular monolayer material (-) graphene oxide (GO). A droplet of a GO solution is formed on a heated polymer substrate, and maintained at steady-state evaporation (all droplet parameters are held constant over time). The polymer substrate is laser patterned to control the droplet's contact line dynamics and the droplet's contact angle is maintained using a computer controlled syringe pump. A room temperature silicon wafer is translated through the vapor field of the evaporating GO droplet using a computer controlled translation stage. Dropwise condensation formed on the silicon wafer is monitored using both optical and infrared cameras. The condensation rate is measured to be ~50pL/mm2?s (-) 500 pL/mm2?s and dependent on the substrate translation speed and height difference between the droplet's apex and substrate surface. Nano-sized GO flakes carried through the vapor phase are captured in the condensate, depositing on the translating wafer. Deposition rate is dependent on the stability of the solution and droplet condensate size. Characterization with Raman spectroscopy show expected shifts for graphene/graphite. The presented EVD technique is promising toward formation of large scale 2D materials with applications to developing new technologies.
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Date Issued: 2015
Identifier: CFE0006035, ucf:50969
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006035

Title: Theoretical And Experimental Investigation Of The Cascading Nature Of Pressure-Swirl Atomization.
Creator: Choudhury, Pretam, Kumar, Ranganathan, Deng, Weiwei, Mansy, Hansen, University of Central Florida
Abstract / Description: Pressure swirl atomizers are commonly used in IC, aero-engines, and liquid propellant rocket combustion. Understanding the atomization process is important in order to enhance vaporization, mitigate soot formation, design of combustion chambers, and improve overall combustion efficiency. This work utilizes non-invasive techniques such as ultra -speed imaging, and Phase Doppler Particle Anemometry (PDPA) in order to investigate the cascade atomization process of pressure-swirl atomizers by...
Show morePressure swirl atomizers are commonly used in IC, aero-engines, and liquid propellant rocket combustion. Understanding the atomization process is important in order to enhance vaporization, mitigate soot formation, design of combustion chambers, and improve overall combustion efficiency. This work utilizes non-invasive techniques such as ultra -speed imaging, and Phase Doppler Particle Anemometry (PDPA) in order to investigate the cascade atomization process of pressure-swirl atomizers by examining swirling liquid film dynamics and the localized droplet characteristics of the resulting hollow cone spray. Specifically, experiments were conducted to examine these effects for three different nozzles with orifice diameters .3mm, .5mm, and .97mm. The ultra-speed imaging allowed for both visualization and interface tracking of the swirling conical film which emanated from each nozzle. Moreover, this allowed for the measurement of the radial fluctuations, film length, cone angle and maximum wavelength. Radial fluctuations are found to be maximum near the breakup or rupture of a swirling film. Film length decreases as Reynolds number increases. Cone angle increases until a critical Reynolds number is reached, beyond which it remains constant. A new approach to analyze the temporally unstable waves was developed and compared with the measured maximum wavelengths. The new approach incorporates the attenuation of a film thickness, as the radius of a conical film expands, with the classical dispersion relationship for an inviscid moving liquid film. This approach produces a new long wave solution which accurately matches the measured maximum wavelength swirling conical films generated from nozzles with the smallest orifice diameter. For the nozzle with the largest orifice diameter, the new long wave solution provides the upper bound limit, while the long wave solution for a constant film thickness provides the lower bound limit. These results indicate that temporal instability is the dominating mechanism which generates long Kelvin Helmholtz waves on the surface of a swirling liquid film. The PDPA was used to measure droplet size and velocity in both the near field and far field of the spray. For a constant Reynolds number, an increase in orifice diameter is shown to increase the overall diameter distribution of the spray. In addition, it was found that the probability of breakup, near the axis, decreases for the largest orifice diameter. This is in agreement with the cascading nature of atomization.
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Date Issued: 2015
Identifier: CFE0006030, ucf:51012
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006030

Title: A Linear Multiplexed Electrospray Thin Film Deposition System.
Creator: Lojewski, Brandon, Deng, Weiwei, Chen, Ruey-Hung, Chen, Quanfang, University of Central Florida
Abstract / Description: Liquid spray is essential to industries requiring processes such as spray coating, spray drying, spray pyrolysis, or spray cooling. This thesis reports the design, fabrication, and characterization of a thin film deposition system which utilizes a linear multiplexed electrospray (LINES) atomizer. First, a thorough review of the advantages and limitations of prior multiplexed electrospray systems leads to discussion of the design rationale for this work. Next, the line of charge model was...
Show moreLiquid spray is essential to industries requiring processes such as spray coating, spray drying, spray pyrolysis, or spray cooling. This thesis reports the design, fabrication, and characterization of a thin film deposition system which utilizes a linear multiplexed electrospray (LINES) atomizer. First, a thorough review of the advantages and limitations of prior multiplexed electrospray systems leads to discussion of the design rationale for this work. Next, the line of charge model was extended to prescribe the operating conditions for the experiments and to estimate the spray profile. The spray profile was then simulated using a Lagrangian model and solved using a desktop supercomputer based on Graphics Processing Units (GPUs). The simulation was extended to estimate the droplet number density flux during deposition. Pure ethanol was electrosprayed in the cone-jet mode from a 51-nozzle aluminum LINES atomizer with less than 3% relative standard deviation in the D10 average droplet diameter as characterized using Phase Doppler Interferometry (PDI). Finally a 25-nozzle LINES was integrated into a thin film deposition system with a heated, motion controlled stage, to deposit TiO2 thin films onto silicon wafers from an ethanol based nanoparticle suspension. The resulting deposition pattern was analyzed using SEM, optical profilometry, and macro photography and compared with the numerical simulation results. The LINES tool developed here is a step forward to enabling the power of electrospray for industrial manufacturing applications in clean energy, health care, and electronics.
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Date Issued: 2013
Identifier: CFE0005106, ucf:50745
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005106

Title: Generation and printing of strictly monodisperse droplets.
Creator: Duan, Hongxu, Deng, Weiwei, An, Linan, Cho, Hyoung, University of Central Florida
Abstract / Description: Highly monodisperse droplets are attracting great attention both in many research areas, such as aerosol science, combustion, and Nano-manufacturing. This thesis invents a novel aerosol generator: (")Periodic Electro Hydro-dynamic Chopper(") termed as (")PEHD chopper("), and develops a new method to directly print micro-patterns with monodisperse droplets. The principle of the PEHD chopper is to use the fringe electric field of a capacitor to introduce controlled perturbation on a liquid jet...
Show moreHighly monodisperse droplets are attracting great attention both in many research areas, such as aerosol science, combustion, and Nano-manufacturing. This thesis invents a novel aerosol generator: (")Periodic Electro Hydro-dynamic Chopper(") termed as (")PEHD chopper("), and develops a new method to directly print micro-patterns with monodisperse droplets. The principle of the PEHD chopper is to use the fringe electric field of a capacitor to introduce controlled perturbation on a liquid jet.We first derived the governing equations for a circular inviscid liquid jet under transverse electric fields. The electric fields were obtained through numerical simulation. Then we used a high speed camera (up to one million frames per second) to visualize the jet break-up as well as the droplets' size and shape.The experiments show that the PEHD chopper can effectively (")chop(") a neutral micro-jet and generate highly monodisperse micro-droplets, which diameter range from 100 (&)#181;m to 500 (&)#181;m. To reduce the droplet size, PEHD chopper with a butterfly design is applied on a typical single electrospray. In this configuration, the jet swings at long wavelengths (?(>)?R), where ?R is the Rayleigh wave length, but breaks up into highly monodisperse droplets near 2?R and ?R without satellite droplets. The butterfly configuration combined with electrified jet expands the diameter range into 20 (&)#181;m to 100 (&)#181;m.Finally, we demonstrate the electrospray printing of Polymer Derived Ceramics (PDC) for sensor applications in harsh environment. A modified single ES with an additional driving electric field is used to directly print PDC precursor without mask, we achieved 1D feature as narrow as 35 (&)#181;m and a micro pentagram pattern. Moreover, after pyrolysis of PDC at 1100 (&)deg;C in nitrogen, amorphous alloys of silicon, carbon and nitrogen (SiCN) are obtained. The samples exhibit excellent good integrity and adhesion to the substrate.
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Date Issued: 2013
Identifier: CFE0005094, ucf:50720
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005094

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.
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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.
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Date Issued: 2013
Identifier: CFE0005081, ucf:50732
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005081

Title: Self-Assembled Two-Component Organic Tubes: Structures and Applications.
Creator: Liang, Wenlang, Fang, Jiyu, Huo, Qun, Deng, Weiwei, University of Central Florida
Abstract / Description: Bile acids are physiologically important metabolites, which are synthesized in liver as the end products of cholesterol metabolism and then secreted into the intestines. They play a critical role in the digestion and absorption of fats and fat-soluble vitamins through emulsifications. The amphipathic and chiral nature of bile acids makes their unique building blocks for assembling supramolecular structures including vesicles, fibers, ribbons and hollow tubes. Lithocholic acid (LCA) is a...
Show moreBile acids are physiologically important metabolites, which are synthesized in liver as the end products of cholesterol metabolism and then secreted into the intestines. They play a critical role in the digestion and absorption of fats and fat-soluble vitamins through emulsifications. The amphipathic and chiral nature of bile acids makes their unique building blocks for assembling supramolecular structures including vesicles, fibers, ribbons and hollow tubes. Lithocholic acid (LCA) is a secondary bile acid. Our studies show LCA can self-assemble into helical tubes in aqueous solution by the linear aggregation and fusion of vesicles. The objective of this dissertation is to tune the structure of helical tubes and functionalize them by the co-assembly of ionic LCA and cationic cetyltrimethylammonium bromide (CTAB) and ionic LCA and cationic cyanine dye (CD), respectively. The first part of this dissertation focuses on the ionic-assembly of LCA and CTAB to synthesize the helical tubes with varied diameters and pitches. Our studies show that LCA and CTAB can self-assemble into helical tubes in NH4OH aqueous solution. The diameter of the helical tubes can be changed by adjusting the molar ratio of LCA and CTAB. The pitch of the helical tubes can be tuned by varying NH4OH concentrations. Differential scanning calorimetry studies indicate that there is a homogeneous composition distribution in the LCA/CTAB helical tubes. X-ray diffraction analysis studies show that the helical tubes have multibilayer walls with an average d-spacing of 4.11nm. We demonstrate that the helical tubes with varied diameters and pitches can be transformed into helical silica through the sol-gel transcription of tetraethoxysilane (TEOS). The second part of this dissertation is to use the ionic self-assembly of LCA and CD to design light-harvesting tubes by mimicking green sulfur bacteria that are known to be a highly efficient photosynthesizer. X-ray diffraction and optical spectra show that LCA and CD can co-assemble into J- or H-aggregate tubes, depending the condition under which the self-assembly occurs. We demonstrate the feasibility of using the J-aggregate nanotubes in the sensitive and selective detection of mercury (II) ions by the photoinduced electron transfer under sunlight. The presence of mercury (II) ions in aqueous solution could be detected for concentrations as low as 10 pM.
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Date Issued: 2013
Identifier: CFE0005201, ucf:50635
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005201

Title: X-ray Radiation Enabled Cancer Detection and Treatment with Nanoparticles.
Creator: Hossain, Mainul, Su, Ming, Behal, Aman, Gong, Xun, Hu, Haiyan, Kapoor, Vikram, Deng, Weiwei, University of Central Florida
Abstract / Description: Despite significant improvements in medical sciences over the last decade, cancer still continues to be a major cause of death in humans throughout the world. Parallel to the efforts of understanding the intricacies of cancer biology, researchers are continuously striving to develop effective cancer detection and treatment strategies. Use of nanotechnology in the modern era opens up a wide range of possibilities for diagnostics, therapies and preventive measures for cancer management....
Show moreDespite significant improvements in medical sciences over the last decade, cancer still continues to be a major cause of death in humans throughout the world. Parallel to the efforts of understanding the intricacies of cancer biology, researchers are continuously striving to develop effective cancer detection and treatment strategies. Use of nanotechnology in the modern era opens up a wide range of possibilities for diagnostics, therapies and preventive measures for cancer management. Although, existing strategies of cancer detection and treatment, using nanoparticles, have been proven successful in case of cancer imaging and targeted drug deliveries, they are often limited by poor sensitivity, lack of specificity, complex sample preparation efforts and inherent toxicities associated with the nanoparticles, especially in case of in-vivo applications. Moreover, the detection of cancer is not necessarily integrated with treatment. X-rays have long been used in radiation therapy to kill cancer cells and also for imaging tumors inside the body using nanoparticles as contrast agents. However, X-rays, in combination with nanoparticles, can also be used for cancer diagnosis by detecting cancer biomarkers and circulating tumor cells. Moreover, the use of nanoparticles can also enhance the efficacy of X-ray radiation therapy for cancer treatment.This dissertation describes a novel in vitro technique for cancer detection and treatment using X-ray radiation and nanoparticles. Surfaces of synthesized metallic nanoparticles have been modified with appropriate ligands to specifically target cancer cells and biomarkers in vitro. Characteristic X-ray fluorescence signals from the X-ray irradiated nanoparticles are then used for detecting the presence of cancer. The method enables simultaneous detection of multiple cancer biomarkers allowing accurate diagnosis and early detection of cancer. Circulating tumor cells, which are the primary indicators of cancer metastasis, have also been detected where the use of magnetic nanoparticles allows enrichment of rare cancer cells prior to detection. The approach is unique in that it integrates cancer detection and treatment under one platform, since, X-rays have been shown to effectively kill cancer cells through radiation induced DNA damage. Due to high penetrating power of X-rays, the method has potential applications for in vivo detection and treatment of deeply buried cancers in humans. The effect of nanoparticle toxicity on multiple cell types has been investigated using conventional cytotoxicity assays for both unmodified nanoparticles as well as nanoparticles modified with a variety of surface coatings. Appropriate surface modifications have significantly reduced inherent toxicity of nanoparticles, providing possibilities for future clinical applications. To investigate cellular damages caused by X-ray radiation, an on-chip biodosimeter has been fabricated based on three dimensional microtissues which allows direct monitoring of responses to X-ray exposure for multiple mammalian cell types. Damage to tumor cells caused by X-rays is known to be significantly higher in presence of nanoparticles which act as radiosensitizers and enhance localized radiation doses. An analytical approach is used to investigate the various parameters that affect the radiosensitizing properties of the nanoparticles. The results can be used to increase the efficacy of nanoparticle aided X-ray radiation therapy for cancer treatment by appropriate choice of X-ray beam energy, nanoparticle size, material composition and location of nanoparticle with respect to the tumor cell nucleus.
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Date Issued: 2012
Identifier: CFE0004547, ucf:49242
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004547

Title: Evaporation, Precipitation Dynamics and Instability of Acoustically Levitated Functional Droplets.
Creator: Saha, Abhishek, Kumar, Ranganathan, Basu, Saptarshi, Kapat, Jayanta, Deng, Weiwei, Shivamoggi, Bhimsen, University of Central Florida
Abstract / Description: Evaporation of pure and binary liquid droplets is of interest in thermal sprays and spray drying of food, ceramics and pharmaceutical products. Understanding the rate of heat and mass transfer in any drying process is important not only to enhance evaporation rate or vapor-gas mixing, but also to predict and control the final morphology and microstructure of the precipitates. Acoustic levitation is an alternative method to study micron-sized droplets without wall effects, which eliminates...
Show moreEvaporation of pure and binary liquid droplets is of interest in thermal sprays and spray drying of food, ceramics and pharmaceutical products. Understanding the rate of heat and mass transfer in any drying process is important not only to enhance evaporation rate or vapor-gas mixing, but also to predict and control the final morphology and microstructure of the precipitates. Acoustic levitation is an alternative method to study micron-sized droplets without wall effects, which eliminates chemical and thermal contamination with surfaces. This work uses an ultrasonic levitation technique to investigate the vaporization dynamics under radiative heating, with focus on evaporation characteristics, precipitation kinetics, particle agglomeration, structure formation and droplet stability. Timescale and temperature scales are developed to compare convective heating in actual sprays and radiative heating in the current experiments. These relationships show that simple experiments can be conducted in a levitator to extrapolate information in realistic convective environments in spray drying. The effect of acoustic streaming, droplet size and liquid properties on internal flow is important to understand as the heat and mass transfer and particle motion within the droplet is significantly controlled by internal motion. Therefore, the droplet internal flow is characterized by Particle Image Velocimetry for different dropsize and viscosity. Nanosuspension droplets suspended under levitation show preferential accumulation and agglomeration kinetics. Under certain conditions, they form bowl shaped structures upon complete evaporation. At higher concentrations, this initial bowl shaped structure morphs into a ring structure. Nanoparticle migration due to internal recirculation forms a density stratification, the location of which depends on initial particle concentration. The time scale of density stratification is similar to that of perikinetic-driven agglomeration of particle flocculation. The density stratification ultimately leads to force imbalance leading to a unique bowl-shaped structure. Chemically active precursor droplet under acoustic levitation shows events such as vaporization, precipitation and chemical reaction leading to nanoceria formation with a porous morphology. The cerium nitrate droplet undergoes phase and shape changes throughout the vaporization process followed by formation of precipitate. Ex-situ analyses using TEM and SEM reveal highly porous morphology with trapped gas pockets and nanoceria crystalline structures at 70 degree C. Inhomogeneity in acoustic pressure around the heated droplet can induce thermal instability. Short wavelength (Kelvin-Helmholtz) instability for diesel and bio-diesel droplets triggers this secondary atomization, which occurs due to relative velocity between liquid and gas phase at the droplet equator. On the other hand, liquids such as Kerosene and FC43 show uncontrollable stretching followed by a catastrophic break-up due to reduction in surface tension and viscosity coupled with inhomogeneity of pressure around the droplet. Finally, a scaling analysis has been established between vaporizing droplets in a convective and radiative environment. The transient temperature normalized by the respective scales exhibits a unified profile for both modes of heating. The analysis allows for the prediction of required laser flux in the levitator experiments to show its equivalence in a corresponding heated gas stream. The theoretical equivalence shows good agreement with experiments for a range of droplet sizes.
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Date Issued: 2012
Identifier: CFE0004436, ucf:49346
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004436

electrospray (5)	+ -
Acoustic Levitation (2)	+ -
Droplet (2)	+ -
Evaporation (2)	+ -
fluid dynamics (2)	+ -

heat transfer (2)	+ -
self-assembly (2)	+ -
2d materials (1)	+ -
5CB (1)	+ -
8CB (1)	+ -
AFM (1)	+ -
Acoustic Streaming (1)	+ -
Acoustically Levitated Droplet (1)	+ -
Aerodynamics (1)	+ -
Aerosol (1)	+ -
Agglomeration (1)	+ -
Alumina (1)	+ -
Biofluids (1)	+ -
Biosening (1)	+ -
Breakup (1)	+ -
CATER (1)	+ -
CNC Micro-Machining (1)	+ -
COMSOL (1)	+ -
Carbon foam (1)	+ -
Cell encapsulation (1)	+ -
Chemical spray pyrolysis (1)	+ -
Coalesecence (1)	+ -
Combustion Instabilities (1)	+ -
Computational fluid dynamics (1)	+ -
Damkohler number (1)	+ -

ETD Collection (28)	+ -
Honors Collection (2)	+ -

University of Central Florida (30)	+ -
Deng, Weiwei (29)	+ -
Kapat, Jayanta (8)	+ -
Kumar, Ranganathan (7)	+ -
Chen, Ruey-Hung (5)	+ -

Chow, Louis (4)	+ -
Fang, Jiyu (4)	+ -
An, Linan (3)	+ -
Basu, Saptarshi (3)	+ -
Gordon, Ali (3)	+ -
Huo, Qun (3)	+ -
Kassab, Alain (3)	+ -
Shivamoggi, Bhimsen (3)	+ -
Divo, Eduardo (2)	+ -
Ilie, Marcel (2)	+ -
Liang, Wenlang (2)	+ -
Mansy, Hansen (2)	+ -
Putnam, Shawn (2)	+ -
Yang, Weiwei (2)	+ -
Aboelsoud, Walid (1)	+ -
Bai, Yuanli (1)	+ -
Behal, Aman (1)	+ -
Bera, Tanmay (1)	+ -
Bernier, Bryan (1)	+ -
Besana, Patrick (1)	+ -
Ceballos, Andres (1)	+ -
Challapalli, Suryanarayana (1)	+ -
Chen, Quanfang (1)	+ -
Cho, Hyong (1)	+ -
Cho, Hyoung (1)	+ -

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