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- Title
- Developing surface engineered liquid crystal droplets for sensing applications.
- Creator
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Bera, Tanmay, Fang, Jiyu, Suryanarayana, Challapalli, Huo, Qun, Cho, Hyong, Deng, Weiwei, Wu, Shintson, University of Central Florida
- Abstract / Description
-
Diagnosis plays a very crucial role in medicine and health care, which makes biosensors extremely important in modern technological context. Till date, various types of biosensors have been developed that are capable of detecting a wide range of biologically important species with great sensitivity and selectivity. However, most of these sensing units require highly sophisticated instrumentation and often lack the desired portability. Liquid crystal (LC) droplets, on the other hand, are a new...
Show moreDiagnosis plays a very crucial role in medicine and health care, which makes biosensors extremely important in modern technological context. Till date, various types of biosensors have been developed that are capable of detecting a wide range of biologically important species with great sensitivity and selectivity. However, most of these sensing units require highly sophisticated instrumentation and often lack the desired portability. Liquid crystal (LC) droplets, on the other hand, are a new type of functional material that are finding increasing research attention as a new sensing unit due to their tunable optical property, high surface area, portability and cost-effectiveness. In this dissertation, functionalized LC droplets for biosensing at aqueous-LC interface are highlighted. Chemically functionalized LC droplets dispersed in aqueous solution were prepared by the self-assembly of amphiphilic molecules at the aqueous/LC interface. These functionalized LC droplets showed a well-defined director of configuration and a specific optical pattern when observed with a polarizing light microscope. It was discovered that the interaction of chemically functionalized LC droplets with an analyte triggers transition of the director of configuration of the LC within the droplets, providing a simple and unique optical sign for the detection of the analyte. Moreover, the director of configuration transition happened in a concentration dependent manner, allowing both qualitative and quantitative detection of the analyte. The sensitivity of chemically functionalized LC droplets depends not only on the nature of amphiphilic molecules but also the size and number of the droplets.The dissertation essentially deals with the application of these chemically functionalized LC droplets in detecting several biologically important species. It was observed that the adsorption of charged macromolecules (dendrimers, proteins, and viruses) on polyelectrolyte functionalized LC droplets triggered a bipolar-to-radial configuration transition based on the polar verses non-polar interaction. By using a simple optical microscope, microgram per milliliter concentrations of bovine serum albumin, cowpea mosaic virus, and tobacco mosaic virus could be detected in aqueous solution. The detection limit of Mastoparan X polypeptide decorated LC droplets in detecting E. coli could reach to approximately 10 bacteria per milliliter. In this case, the high affinity of the polypeptide towards the bacterial causes the former to detach from the LC droplets, triggering the director of configuration transition of the LC inside the droplets. Finally, surfactant decorated LC droplets were used to detect lithocholic acid (LCA), a toxic bile acid used as a specific biomarker for colon cancers. In this case, the director of configuration transition of the LC inside the droplets is a result of the replacement of the surfactant from the aqueous/LC interface by LCA. The microgram per milliliter concentration of LCA, a clinically significant concentration, could be easily detected by changing the length of surfactants. These studies highlight the novel use of surface functionalized LC droplets to detect biologically important species. Due to their tunable optical property, coupled with high surface area and portability, surface functionalized LC droplets have great potentials in the design of next generation biosensors.
Show less - Date Issued
- 2012
- Identifier
- CFE0004307, ucf:49471
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004307
- Title
- Laser Spark Ignition of Counter-flow Diffusion Flames: Effects of diluents and diffusive-thermal properties.
- Creator
-
Sime Segura, Fidelio, Deng, Weiwei, Chen, Ruey-Hung, Kapat, Jayanta, University of Central Florida
- Abstract / Description
-
A pulsed Nd:YAG laser is used to study laser spark ignition of methane counter-flow diffusion flames with the use of helium and argon as diluents to achieve a wide range of variations in transport properties. The global strain rate and Damk(&)#246;hler number on successful ignition were investigated for the effects of Lewis number and transport properties, which are dependent on the diluent type and dilution level. A high-speed camera is used to record the ignition events and a software is...
Show moreA pulsed Nd:YAG laser is used to study laser spark ignition of methane counter-flow diffusion flames with the use of helium and argon as diluents to achieve a wide range of variations in transport properties. The global strain rate and Damk(&)#246;hler number on successful ignition were investigated for the effects of Lewis number and transport properties, which are dependent on the diluent type and dilution level. A high-speed camera is used to record the ignition events and a software is used for pre-ignition flow field and mixing calculations. It is found that the role of effective Lewis number on the critical global strain rate, beyond which ignition is not possible, is qualitatively similar that on the extinction strain rate. With the same level of dilution, the inert diluent with smaller Lewis number yields larger critical global strain rate. The critical Damk(&)#246;hler number below which no ignition is possible is found to be within approximately 20% for all the fuel-inert gas mixtures studied. When successful ignition takes place, the ignition time increases as the level of dilution of argon is increased. The ignition time decreases with increasing level of helium dilution due to decreases in thermal diffusion time, which causes rapid cooling of the flammable layer during the ignition process. However, the critical strain for ignition with helium dilution rapidly decreases as the dilution level is increased. The experimental results show that with the increase of strain rate the time to steady flame decreases, and that with the increase of dilution level time for the flame to become steady increases. For the same level of dilution, the time for steady flame is observed to be longer for He-diluted flames than for Ar-diluted flames due to its thermal diffusivity being larger than that of Ar.
Show less - Date Issued
- 2012
- Identifier
- CFE0004295, ucf:49467
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004295
- Title
- Development of Polymer Derived SiAlCN Ceramic and Its Applications for High-Temperature Sensors.
- Creator
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Shao, Gang, An, Linan, Fang, Jiyu, Xu, Chengying, Chow, Lee, Deng, Weiwei, University of Central Florida
- Abstract / Description
-
Polymer-derived ceramic (PDC) is the name for a class of materials synthesized by thermal decomposition of polymeric precursors which excellent thermomechanical properties, such as high thermal stability, high oxidation/corrosion resistance and high temperature multifunctionalities. Direct polymer-to-ceramic processing routes of PDCs allow easier fabrication into various components/devices with complex shapes/structures. Due to these unique properties, PDCs are considered as promising...
Show morePolymer-derived ceramic (PDC) is the name for a class of materials synthesized by thermal decomposition of polymeric precursors which excellent thermomechanical properties, such as high thermal stability, high oxidation/corrosion resistance and high temperature multifunctionalities. Direct polymer-to-ceramic processing routes of PDCs allow easier fabrication into various components/devices with complex shapes/structures. Due to these unique properties, PDCs are considered as promising candidates for making high-temperature sensors for harsh environment applications, including high temperatures, high stress, corrosive species and/or radiation. The SiAlCN ceramics were synthesized using the liquid precursor of polysilazane (HTT1800) and aluminum-sec-tri-butoxide (ASB) as starting materials and dicumyl peroxide (DP) as thermal initiator. The as-received SiAlCN ceramics have very good thermal-mechanical properties and no detectable weight loss and large scale crystallization. Solid-state NMR indicates that SiAlCN ceramics have the SiN4, SiO4, SiCN3, and AlN5/AlN6 units. Raman spectra reveals that SiAlCN ceramics contain (")free carbon(") phase with two specific Raman peaks of (")D(") band and (")G(") band at 1350 cm-1 and 1600 cm-1, respectively. The (")free carbon(") becomes more and more ordered with increasing the pyrolysis temperature. EPR results show that the defects in SiAlCN ceramics are carbon-related with a g-factor of 2.0016(&)#177;0.0006. Meanwhile, the defect concentration decreases with increasing sintered temperature, which is consistent with the results obtained from Raman spectra.Electric and dielectric properties of SiAlCN ceramics were characterized. The D.C. conductivity of SiAlCN ceramics increases with increasing sintered temperature and the activation energy is about 5.1 eV which higher than that of SiCN ceramics due to the presence of oxygen. The temperature dependent conductivity indicates that the conducting mechanism is a semiconducting band-gap model and follows the Arrhenius equation with two different sections of activation energy of 0.57 eVand 0.23 eV, respectively. The temperature dependent conductivity makes SiAlCN ceramics suit able for high temperature sensor applications. The dielectric properties were carried out by the Agilent 4298A LRC meter. The results reveal an increase in both dielectric constant and loss with increasing temperature (both pyrolysis and tested). Dielectric loss is dominated by the increasing of conductivity of SiAlCN ceramics at high sintered temperatures.SiAlCN ceramic sensors were fabricated by using the micro-machining method. High temperature wire bonding issues were solved by the integrity embedded method (IEM). It's found that the micro-machining method is a promising and cost-effective way to fabricate PDC high temperature sensors. Moreover IEM is a good method to solve the high temperature wire bonding problems with clear bonding interface between the SiAlCN sensor head and Pt wires. The Wheatstone bridge circuit is well designed by considering the resistance relationship between the matching resistor and the SiAlCN sensor resistor. It was found that the maximum sensitivity can be achieved when the resistance of matching resistor is equal to that of the SiAlCN sensor. The as-received SiAlCN ceramic sensor was tested up to 600 degree C with the relative output voltage changing from -3.932 V to 1.153 V. The results indicate that the relationship between output voltage and test temperature is nonlinear. The tested sensor output voltage agrees well with the simulated results. The durability test was carried out at 510 degree C for more than two hours. It was found that the output voltage remained constant for the first 30 min and then decreased gradually afterward by 0.02, 0.04 and 0.07 V for 1, 1.5 and 2 hours.
Show less - Date Issued
- 2013
- Identifier
- CFE0004937, ucf:49602
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004937
- Title
- Effect of particles on evaporation of droplet containing particles.
- Creator
-
Wei, Yan, Chen, Ruey-Hung, Deng, Weiwei, Putnam, Shawn, Wu, Thomas, University of Central Florida
- Abstract / Description
-
The evaporation of droplet containing insoluble particles has grown into an active area of research due to the needs for nanofluids for applications in heat transfer, combustion, and manufacturing desired micro/nano particles in the pharmaceutical industry. The evaporation of droplets containing particles involves complicated multiphase heat and mass transport. The evaporation process consists of two stages: the first stage consists of evaporation until a shell of particle forms or when the...
Show moreThe evaporation of droplet containing insoluble particles has grown into an active area of research due to the needs for nanofluids for applications in heat transfer, combustion, and manufacturing desired micro/nano particles in the pharmaceutical industry. The evaporation of droplets containing particles involves complicated multiphase heat and mass transport. The evaporation process consists of two stages: the first stage consists of evaporation until a shell of particle forms or when the solid to liquid ratio is sufficiently large and the second stage, where the droplet size is commonly assumed to be unchanged. The dissertation investigates the evaporation kinetics in the first stage. An experimental setup based on electrodynamic balance (EDB) is built to allow the observation of evaporation of a free standing micro size droplet. Besides experimental design, a novel theoretical model is developed to first describe the morphological evolution process in the absence of internal convection. The model accounts for the effect of particles at the droplet surface on the diffusion of liquid vapor. The gradually increasing particle number at the droplet surface reduces the area for evaporation, leading to reduction in evaporation rate in the first drying stage, contrary to previous assumptions. The evaporation in the first stage is controlled by Pe (defined as the ratio of droplet evaporation rate to the particle diffusion rate) and particle properties such as wettability. For large values of Pe, the particles concentration is high near the droplet surface, leading to the change of evaporation rate. For small values of Pe, the effect of particles on the evaporation rate of droplet in the first drying stage is small because particles are allowed sufficient time to redistribute within the droplet. The model analysis also reveals that particle wettability is an important factor affecting the first drying stage. For hydrophilic particles, the contact angle of the particles at the droplet surface is small, leading to small change of evaporation in the first stage. For the hydrophobic particles that have large contact angles, the change of evaporation rate in the first drying stage is larger. The evaporation model that accounts for the internal convection is also used to describe the evaporation process. In this model, the evaporation behavior during the first stage is controlled by the particle mobility, initial particle concentration, and droplet recession/evaporation rate. For particles with high mobility, the particle distribution within the droplet tends to be smooth. The effect of convection flow on the particles distribution becomes stronger as particle mobility decreases. Once the particles mobility is decreased to a limit at which the surface particle density is only controlled by the internal flow and the evaporation process is independent of the particles mobility. For a given internal flow field and a specific particles mobility, the duration of the first stage and the final dry particle size are both controlled by the initial particle concentration. A smaller/larger initial particle concentration results in a longer/shorter first stage and smaller/larger dry particle.
Show less - Date Issued
- 2015
- Identifier
- CFE0005903, ucf:50856
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005903
- Title
- Thermally induced motion, collision and mixing of levitated droplets.
- Creator
-
Davanlou, Ashkan, Kumar, Ranganathan, Cho, Hyoung Jin, Deng, Weiwei, Mansy, Hansen, Shivamoggi, Bhimsen, University of Central Florida
- Abstract / Description
-
This dissertation investigates the motion of a levitated droplet experimentally and analytically against the Marangoni flow in an immiscible outer fluid at higher speeds than is possible currently. Based on our earlier experiments, when a droplet is released from a height of 1.5 (-) 4 times its diameter from the liquid surface, it can overcome the impact and stay levitated at the liquid-air interface due to the existence of an air gap between the droplet and the liquid film. In order to...
Show moreThis dissertation investigates the motion of a levitated droplet experimentally and analytically against the Marangoni flow in an immiscible outer fluid at higher speeds than is possible currently. Based on our earlier experiments, when a droplet is released from a height of 1.5 (-) 4 times its diameter from the liquid surface, it can overcome the impact and stay levitated at the liquid-air interface due to the existence of an air gap between the droplet and the liquid film. In order to explain this behavior of droplet traveling against the counter-current motion, we propose a simple approach: first, the Marangoni convection inside the thin film is considered without the droplet floating on the surface. By using a level-set method and solving the Navier-Stokes equation, the free surface velocity and deformation are calculated. Then, these quantities are used to solve for droplet velocity and drag coefficient simultaneously using a force balance. In order to compare the simulation results, experiments with levitated water droplets on an immiscible carrier liquid, FC-43, were conducted for various temperature gradients, and droplet velocities were measured at different locations using high-speed imaging. The experimental results are in good agreement with the developed theoretical model. For a Reynolds number range of 2-32, it is shown that the drag coefficients are up to 66% higher than those for the fully immersed sphere at the same Reynolds numbers. A correlation is proposed to calculate the drag coefficient of levitated droplets for various temperature drops across the channel.For the first time, it is shown that it is possible to realize the natural coalescence of droplets through Marangoni effect without any external stimulation, and deliver the coalesced droplet to a certain destination through the use of surface tension gradients. The effects of the various shapes and sizes upon collision are studied. Regions of coalescence and stretching separation of colliding droplets are delineated based on Weber number and impact number. The existence of the transition line between coalescence and stretching separation in this passive mode of transport is similar to what was observed in the literature for forced coalescence at significantly higher Weber numbers. It is also found that a thermocapillary environment improves the mixing process. In order to illustrate and quantify the mixing phenomenon, the dispensed droplets were made of potassium hydroxide and phenolphthalein which is used as a pH indicator. The experiments show the possibility to reach mixing rates as high as 74% within 120 ms. This study offers new insight to thermo-coalescence and demonstrates how natural coalescence could be used to transport, mix and collect biochemical assays more efficiently. The results of this research can be engineered to enhance the performance of self-cleaning surfaces and micro-total analysis systems ((&)#181;TAS), where sample transport, filtration, chemical reactions, separation and detection are of great interest.
Show less - Date Issued
- 2015
- Identifier
- CFE0006213, ucf:51106
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006213
- Title
- Combustion Instability Mechanism of a Reacting Jet in Cross Flow at Gas Turbine Operating Conditions.
- Creator
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Pent, Jared, Kapat, Jayanta, Deng, Weiwei, Gordon, Ali, Vasu Sumathi, Subith, Martin, Scott, University of Central Florida
- Abstract / Description
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Modern gas turbine designs often include lean premixed combustion for its emissions benefits; however, this type of combustion process is susceptible to self-excited combustion instabilities that can lead to damaging heat loads and system vibrations. This study focuses on identifying a mechanism of combustion instability of a reacting jet in cross flow, a flow feature that is widely used in the design of gas turbine combustion systems. Experimental results from a related study are used to...
Show moreModern gas turbine designs often include lean premixed combustion for its emissions benefits; however, this type of combustion process is susceptible to self-excited combustion instabilities that can lead to damaging heat loads and system vibrations. This study focuses on identifying a mechanism of combustion instability of a reacting jet in cross flow, a flow feature that is widely used in the design of gas turbine combustion systems. Experimental results from a related study are used to validate and complement three numerical tools that are applied in this study (-) self-excited Large Eddy Simulations, 3D thermoacoustic modeling, and 1D instability modeling. Based on the experimental and numerical results, a mechanism was identified that included a contribution from the jet in cross flow impedance as well as an overall jet flame time lag. The jet impedance is simply a function of the acoustic properties of the geometry while the flame time lag can be separated into jet velocity, equivalence ratio, and strain fluctuations, depending on the operating conditions and setup. For the specific application investigated in this study, it was found that the jet velocity and equivalence ratio fluctuations are important, however, the effect of the strain fluctuations on the heat release are minimal due to the high operating pressure. A mathematical heat release model was derived based on the proposed mechanism and implemented into a 3D thermoacoustic tool as well as a 1D instability tool. A three-point stability trend observed in the experimental data was correctly captured by the 3D thermoacoustic tool using the derived heat release model. Stability maps were generated with the 1D instability tool to demonstrate regions of stable operation that can be achieved as a function of the proposed mechanism parameters. The relative effect of the reacting jet in cross flow on the two dominant unstable modes was correctly captured in the stability maps. While additional mechanisms for a reacting jet in cross flow are possible at differing flow conditions, the mechanism proposed in this study was shown to correctly replicate the stability trends observed in the experimental tests and provides a fundamental understanding that can be applied for combustion system design.
Show less - Date Issued
- 2014
- Identifier
- CFE0005687, ucf:50154
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005687
- Title
- A COUPLED CFD-LUMPED PARAMETER MODEL OF THE HUMAN CIRCULATION: ELUCIDATING THE HEMODYNAMICS OF THE HYBRID NORWOOD PALLIATIVE TREATMENT AND EFFECTS OF THE REVERSE BLALOCK-TAUSSIG SHUNT PLACEMENT AND DIAMETER.
- Creator
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Ceballos, Andres, Kassab, Alain, Bai, Yuanli, Deng, Weiwei, DeCampli, William, Divo, Eduardo, University of Central Florida
- Abstract / Description
-
The Hybrid Norwood (HN) is a relatively new first stage procedure for neonates with Hypoplastic Left Heart Syndrome (HLHS), in which a sustainable univentricular circulation is established in a less invasive manner than with the standard procedure. A computational multiscale model of such HLHS circulation following the HN procedure was used to obtain detailed hemodynamics. Implementation of a reverse-BT shunt (RBTS), a synthetic bypass from the main pulmonary to the innominate artery placed...
Show moreThe Hybrid Norwood (HN) is a relatively new first stage procedure for neonates with Hypoplastic Left Heart Syndrome (HLHS), in which a sustainable univentricular circulation is established in a less invasive manner than with the standard procedure. A computational multiscale model of such HLHS circulation following the HN procedure was used to obtain detailed hemodynamics. Implementation of a reverse-BT shunt (RBTS), a synthetic bypass from the main pulmonary to the innominate artery placed to counteract aortic arch stenosis, and its effects on local and global hemodynamics were studied.A synthetic and a 3D reconstructed, patient derived anatomy after the HN procedure were utilized, with varying degrees of distal arch obstruction, or stenosis, (nominal and 90% reduction in lumen) and varying RBTS diameters (3.0, 3.5, 4.0 mm). A closed lumped parameter model (LPM) for the peripheral or distal circulation coupled to a 3D Computational Fluid Dynamics (CFD) model that allows detailed description of the local hemodynamics was created for each anatomy. The implementation of the RBTS in any of the chosen diameters under severe stenosis resulted in a restoration of arterial perfusion to near-nominal levels. Shunt flow velocity, vorticity, and overall wall shear stress levels are inverse functions of shunt diameter, while shunt perfusion and systemic oxygen delivery correlates positively with diameter. No correlation of shunt diameter with helicity was recorded.In the setting of the hybrid Norwood circulation, our results suggest: (1) the 4.0mm RBTS may be more thrombogenic when implemented in the absence of severe arch stenosis and (2) the 3.0mm and 3.5mm RBTS may be a more suitable alternative, with preference to the latter since it provides similar hemodynamics at lower levels of wall shear stress.
Show less - Date Issued
- 2015
- Identifier
- CFE0005772, ucf:50068
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005772
- Title
- Modeling and Spray Pyrolysis Processing of Mixed Metal Oxide Nano-Composite Gas Sensor Films.
- Creator
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Khatami, Seyed Mohammad Navid, Ilegbusi, Olusegun, Deng, Weiwei, Kassab, Alain, Coffey, Kevin, Divo, Eduardo, University of Central Florida
- Abstract / Description
-
The role of sensor technology is obvious in improvement and optimization of many industrial processes. The sensor films, which are considered the core of chemical sensors, have the capability to detect the presence and concentration of a specific chemical substance. Such sensor films achieve selectivity by detecting the interaction of the specific chemical substance with the sensor material through selective binding, adsorption and permeation of analyte. This research focuses on development...
Show moreThe role of sensor technology is obvious in improvement and optimization of many industrial processes. The sensor films, which are considered the core of chemical sensors, have the capability to detect the presence and concentration of a specific chemical substance. Such sensor films achieve selectivity by detecting the interaction of the specific chemical substance with the sensor material through selective binding, adsorption and permeation of analyte. This research focuses on development and verification of a comprehensive mathematical model of mixed metal oxide thin film growth using spray pyrolysis technique (SPT). An experimental setup is used to synthesize mixed metal oxide films on a heated substrate. The films are analyzed using a variety of characterization tools. The results are used to validate the mathematical model. There are three main stages to achieve this goal: 1) A Lagrangian-Eulerian method is applied to develop a CFD model of atomizing multi-component solution. The model predicts droplet characteristics in flight, such as spatial distribution of droplet size and concentration. 2) Upon reaching the droplets on the substrate, a mathematical model of multi-phase transport and chemical reaction phenomena in a single droplet is developed and used to predict the deposition of thin film. The various stages of droplet morphology associated with surface energy and evaporation are predicted. 3) The processed films are characterized for morphology and chemical composition (SEM, XPS) and the data are used to validate the models as well as investigate the influence of process parameters on the structural characteristics of mixed metal oxide films. The structural characteristics are investigated of nano structured thin films comprising of ZnO, SnO2, ZnO+In2O3 and SnO2+In2O3 composites. The model adequately predicts the size distribution and film thickness when the nanocrystals are well-structured at the controlled temperature and concentration.
Show less - Date Issued
- 2014
- Identifier
- CFE0005817, ucf:50048
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005817
- Title
- Experimental Investigation of Breakup and Coalescence Characteristics of a Hollow Cone Swirling Spray.
- Creator
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Lee, Joshua, Kumar, Ranganathan, Deng, Weiwei, Kapat, Jayanta, Basu, Saptarshi, Shivamoggi, Bhimsen, University of Central Florida
- Abstract / Description
-
Atomization can be achieved by discharging liquid at relative high velocities into a slow moving environment (hydraulic nozzles) or by discharging liquid at low velocities into a fast moving gas flow (air-blast nozzles). These two types of injector nozzles are featured in majority of the industry applications such as power generation, food or pharmaceutical powder formation, spray painting, petroleum refining, and thermal sprays. The most common atomizer used in combustion engines is the...
Show moreAtomization can be achieved by discharging liquid at relative high velocities into a slow moving environment (hydraulic nozzles) or by discharging liquid at low velocities into a fast moving gas flow (air-blast nozzles). These two types of injector nozzles are featured in majority of the industry applications such as power generation, food or pharmaceutical powder formation, spray painting, petroleum refining, and thermal sprays. The most common atomizer used in combustion engines is the pressure-swirl nozzle (Simplex nozzle) to obtain a homogenous mixture at different equivalence ratios. The experimental studies performed with pressure-swirl nozzles have reported contradictory results over the last few years. Thus, the fundamentals of spray dynamics, such as spray formation, liquid breakup length, droplet breakup regimes, and coalescence still need to be understood for a pressure-swirl nozzle.An experimental study of the breakup characteristics of various liquids and fuels with different thermal physical properties emanating from hollow cone hydraulic injector nozzles induced by pressure-swirling was investigated. The experiments were conducted using two nozzles with different orifice diameters 0.3mm and 0.5mm and injection pressures (0.3-4MPa) which correspond to Rep = 7,000-31,000 depending on the liquids being tested. Three laser-based techniques, i.e., Shadowgraph, Particle Image Velocimetry (PIV) and Phase Doppler Particle Anemometry (PDPA) were utilized in this study. Although each technique had its limitation in different flow regimes, the results were cross-validated, and generally showed correct trends in axial and radial measurements of velocity and diameter for different nozzles, Weber and Reynolds numbers.The spatial variation of diameter and velocity arises principally due to primary breakup of liquid films and subsequent secondary breakup of large droplets due to aerodynamic shear. Downstream of the nozzle, coalescence of droplets due to collision is also found to be significant. Different types of liquid film break up was considered and found to match well with the theory. The spray is subdivided into three zones: near the nozzle, a zone consisting of film and ligament regime, where primary breakup and some secondary breakup take place; a second zone where the secondary breakup process continues, but weakens, and the centrifugal dispersion becomes dominant, and a third zone away from the spray where coalescence is dominant. Each regime has been analyzed in detail to understand the effect of surface tension and viscosity. Surface tension and viscosity were engineered to mimic fuels, which were then compared with real fuels such as Ethanol, Jet-A and Kerosene. Results show similarity in the diameter in the beginning stages of breakup but in the coalescence regime, the values deviate from each other, indicating that the vapor pressure also plays a major role in this regime.
Show less - Date Issued
- 2013
- Identifier
- CFE0005021, ucf:50014
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005021
- Title
- Agglomeration, Evaporation and Morphological Changes in Droplets with Nanosilica and Nanoalumina Suspensions in an Acoustic Field.
- Creator
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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
