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Title: FREQUENCY-DOMAIN FARADAY ROTATION SPECTROSCOPY (FD-FRS) FOR FUNCTIONALIZED PARTICLE AND BIOMOLECULE CHARACTERIZATION.
Creator: Murdock, Richard, Putnam, Shawn, University of Central Florida
Abstract / Description: In this study, the magnetically-induced vibrations of functionalized magnetic particle suspensions were probed for the development of a novel optical spectroscopy technique. Through this work (1) the frequency-dependence of the faraday rotation in ferrofluids and (2) the extension of this system to elucidating particle size and conformation as an alternative immunoassay to costly and labor/time intensive Western Blotting and ELISA has been shown. With its sensitivity and specificity, this...
Show moreIn this study, the magnetically-induced vibrations of functionalized magnetic particle suspensions were probed for the development of a novel optical spectroscopy technique. Through this work (1) the frequency-dependence of the faraday rotation in ferrofluids and (2) the extension of this system to elucidating particle size and conformation as an alternative immunoassay to costly and labor/time intensive Western Blotting and ELISA has been shown. With its sensitivity and specificity, this method has proven to be a promising multi-functional tool in biosensing, diagnostic, and therapeutic nanomedicine efforts. Due to its ubiquitous nature in all optically-transparent materials, the faraday rotation, or circular birefringence, was developed as a robust and sensitive nanoscale biomolecule characterization technique through Brownian relaxation studies of particle suspensions. Current efforts have shown the applicability of this phenomenon in solid, pure liquid, and colloidal samples as well as simultaneous advancements of magnetic nanoparticle research in the magnetometric and magneto-optical regimes. By merging these two fields, a clinically relevant spectroscopy (fd-FRS, Frequency Domain Faraday Rotation Spectroscopy) was developed based on a newly revised model stemming from Debye relaxation theory. Through this work, an optical bench with a variable permeability core electromagnet and a frequency-domain lock-in amplifier setup (DC to 20 kHz) have been used to distinguish between Fe3O4-core nanoparticles with functionalization layers of PEG4/PEG8 polymer with future applications involving the Anti-BSA/BSA antibody/antigen couple. Particle concentrations down to 500 nM (magnetic nanoparticles) and 0.01 Volume % (magnetic beads) were studied with diameters ranging from ~200 nm to 1 um. Currently, the characteristic peak corresponding to the out-of-phase relaxation of the suspended particles has been elusive, despite a wide particle size distribution and the use of a balanced photodetector. Future work will involve highly monodisperse samples, faster scan times, and thermal characterization applications of fd-FRS.
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Date Issued: 2015
Identifier: CFH0004813, ucf:45467
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004813

Title: EXPERIMENTAL AND NUMERICAL INVESTIGATIONS OF MICRODROPLET EVAPORATION WITH A FORCED PINNED CONTACT LINE.
Creator: Gleason, Kevin, Putnam, Shawn, University of Central Florida
Abstract / Description: Experimental and numerical investigations of water microdroplet evaporation on heated, laser patterned polymer substrates are reported. The study is focused on both (1) validating numerical models with experimental data, (2) identifying how changes in the contact line influences evaporative heat transfer and (3) determining methods of controlling contact line dynamics during evaporation. Droplets are formed using a bottom-up methodology, where a computer-controlled syringe pump supplies water...
Show moreExperimental and numerical investigations of water microdroplet evaporation on heated, laser patterned polymer substrates are reported. The study is focused on both (1) validating numerical models with experimental data, (2) identifying how changes in the contact line influences evaporative heat transfer and (3) determining methods of controlling contact line dynamics during evaporation. Droplets are formed using a bottom-up methodology, where a computer-controlled syringe pump supplies water to a ~200 um in diameter fluid channel within the heated substrate. This methodology facilitates precise control of the droplets growth rate, size, and inlet temperature. In addition to this microchannel supply line, the substrate surfaces are laser patterned with a moat-like trench around the fluid-channel outlet, adding additional control of the droplets contact line motion, area, and contact angle. In comparison to evaporation on non-patterned substrate surfaces, this method increases the contact line pinning time by ~60% of the droplets lifetime. The evaporation rates are compared to the predictions of a commonly reported model based on a solution of the Laplace equation, providing the local evaporation flux along the droplets liquid-vapor interface. The model consistently overpredicts the evaporation rate, which is presumable due to the models constant saturated vapor concentration along the droplets liquid-vapor interface. In result, a modified version of the model is implemented to account for variations in temperature along the liquid-vapor interface. A vapor concentration distribution is then imposed using this temperature distribution, increasing the accuracy of predicting the evaporation rate by ~7.7% and ~9.9% for heated polymer substrates at Ts = 50C and 65C, respectively.
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Date Issued: 2014
Identifier: CFH0004566, ucf:45212
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004566

Title: Investigation of Novel Fin Structures Enhancing Micro Heat Sink Thermal Performance.
Creator: Ismayilov, Fuad, Peles, Yoav, Kassab, Alain, Putnam, Shawn, Akturk, Ali, University of Central Florida
Abstract / Description: Operating temperature in electronics applications is continuously increasing. Therefore, for the past few decades, high heat flux removing micro heat sinks are investigated in terms of heat transfer effectiveness. This study generally concentrates on improving the passive heat transfer techniques. Micro heat sinks used in experiments are fabricated using MEMS techniques. Resistance temperature detectors, RTDs, were used for temperature measurements. The experimental data was obtained for...
Show moreOperating temperature in electronics applications is continuously increasing. Therefore, for the past few decades, high heat flux removing micro heat sinks are investigated in terms of heat transfer effectiveness. This study generally concentrates on improving the passive heat transfer techniques. Micro heat sinks used in experiments are fabricated using MEMS techniques. Resistance temperature detectors, RTDs, were used for temperature measurements. The experimental data was obtained for single and two phase flow regions; however, only single phase flow results were considered in numerical simulations. Numerical validations were performed on the micro heat sinks, including cylinder and hydrofoil shaped pin fins. Following the validation phase, optimization has been performed to further improve the hydraulic and thermal performance. DOE study showed that the chord length and leading edge size of the hydrofoil pin fin are significant contributors to the thermal performance. The ranges of geometrical variables were identified and fed into multi-objective optimization cycles implementing the multi-objective genetic algorithm. The optimization objectives were to minimize pumping requirements while enhancing the local and global heat transfer effectiveness over the surface of the heater in single phase flow environment. A broad range of geometries were obtained with an acceptable tradeoff between thermal and hydraulic performance for low Reynolds number. Additionally, tandem geometries were investigated and showed that higher heat transfer effectiveness could be obtained with acceptable pumping power requirements. The importance of such optimization studies before the experimental testing is highlighted, and novel geometries are presented for further experimental investigations. Thermal performance improvement of 28% was obtained via implementing proposed geometries with only a 12% pressure drop increase. Local heat transfer optimization, aiming to decrease the local temperatures were also performed using doublet pin fin configurations. Results showed that tandem hydrofoils could control the flow with minimum pressure drops while reaching the desired low local temperatures.
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Date Issued: 2019
Identifier: CFE0007821, ucf:52828
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007821

Title: Thermodynamic Modeling and Transient Simulation of a Low-Pressure Heat Recovery Steam Generator Using Siemens T3000.
Creator: Caesar, Andres, Das, Tuhin, Bhattacharya, Samik, Putnam, Shawn, University of Central Florida
Abstract / Description: With world energy consumption rising, and nonrenewable energy resources quickly depleting, it is essential to design more efficient power plants and thereby economically utilize fossil fuels. To that end, this work focuses on the thermodynamic modeling of steam power systems to enhance our understanding of their dynamic and transient behavior. This thesis discusses the physical phenomena behind a heat recovery steam generator (HRSG) and develops a mathematical description of its system...
Show moreWith world energy consumption rising, and nonrenewable energy resources quickly depleting, it is essential to design more efficient power plants and thereby economically utilize fossil fuels. To that end, this work focuses on the thermodynamic modeling of steam power systems to enhance our understanding of their dynamic and transient behavior. This thesis discusses the physical phenomena behind a heat recovery steam generator (HRSG) and develops a mathematical description of its system dynamics. The model is developed from fundamentals of fluid dynamics, phase change, heat transfer, conservation laws and unsteady flow energy equations. The resulting model captures coupled physical phenomena with acceptable accuracy while achieving fast, and potentially real-time, simulations. The computational HRSG model is constructed in the Siemens T3000 platform. This work establishes the dynamic modeling capability of T3000, which has traditionally been used for programming control algorithms. The validation objective of this project is to accurately simulate the transient response of an operational steam power system. Validation of the T3000 model is carried out by comparing simulation results to start-up data from the low-pressure system of a Siemens power plant while maintaining the same inlet conditions. Simulation results well correlate with plant data regarding transient behavior and equilibrium conditions. With a comprehensive HRSG model available, it will allow for further research to take place, and aid in the advancement of steam power system technology. Some future research areas include the extension to intermediate and high-pressure system simulations, combined simulation of all three pressure stages, and continued improvement of the boiler model. In addition to enabling model-based prediction and providing further insight, this effort will also lead to controller design for improved performance.
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Date Issued: 2018
Identifier: CFE0007562, ucf:52599
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007562

Title: Pressurized Metal Bellows Shock Absorber for Space Applications.
Creator: Trautwein, John, Kauffman, Jeffrey, Raghavan, Seetha, Putnam, Shawn, University of Central Florida
Abstract / Description: Numerous spacecraft designs exist for exploring the surfaces of planetary bodies and each have their own advantages and disadvantages. All successful landings have been made by stationary landers or wheeled rovers that rely on one-time use mechanisms, such as crushable aluminum honeycomb shock absorbers or inflatable airbags, to reduce shock loading to the spacecraft during landing. The stationary lander is the simplest type of lander, but can only take data from one location. Wheeled rovers...
Show moreNumerous spacecraft designs exist for exploring the surfaces of planetary bodies and each have their own advantages and disadvantages. All successful landings have been made by stationary landers or wheeled rovers that rely on one-time use mechanisms, such as crushable aluminum honeycomb shock absorbers or inflatable airbags, to reduce shock loading to the spacecraft during landing. The stationary lander is the simplest type of lander, but can only take data from one location. Wheeled rovers add complexity in exchange for mobility to explore different locations. Rovers are limited by the terrain they can traverse; rovers becoming stuck have ended missions. In contrast to rovers and stationary landers, hoppers explore by making multiple launch and landing hops. They have the advantage of being able to avoid terrain that would cause a rover to become stuck. A hopper may require a landing shock absorber that can reliably operate multiple times in harsh environments.Most terrestrial shock absorbers use hydraulic fluid, allowing for compact and inexpensive devices. Hydraulics have been used in space applications, but require thermal controls to maintain the proper fluid viscosity. They also require dynamic seals which, in the case of a leak, can degrade performance, shorten mission life, and contaminate sensitive science equipment. Leakage is also a concern in pressurized systems in space because missions can take decades from when a system is installed to when it actually is used.To address these issues, a pressurized metal bellows shock absorber is proposed. This shock absorber could operate at nearly any expected spacecraft environment. Metal bellows are designed to operate from cryogenic temperatures to several hundred degrees Celsius. A hermetically sealed system eliminates the risks of a system with seals. Metal bellows are in common use for terrestrial harsh environments and vacuum applications. Small metal bellows are used as dampers for pressure control systems with small displacements.Models for the dynamics of this device are developed and presented here. Starting from the ideal gas law, polytropic compression, and compressible flow through an orifice, differential equations of motion and pressure are derived. These equations are nonlinear for the displacements under consideration and are nondimensionalized to help provide insight. Equations for static equilibrium, maximum initial displacement bounds, and estimated natural frequency are presented.Metal bellows can operate as a passive damper with a simple orifice between the control volumes. Optimization is performed for the nondimensional model of a passive damper. Because the response is highly nonlinear, a method is developed to estimate a damping coefficient that is used as the objective function for this optimization. Feasibility of this concept is investigated through an example design problem using data from a metal bellows manufacturer as constraints. An optimal mass configuration is found that meets the design constraints. Performance can be improved over the passive system by adding control. The first control strategy involves a check valve, such that the effective orifice size varies between compression and extension. The next control strategy replaces the orifice with a control valve. Varying the valve opening and closing timing can achieve optimal performance. Finally, using the metal bellows as an actuator to help launch the hopper is investigated. While the valve is closed, the gas in the second volume is compressed. Then the valve is opened the hopper is launched.The results of this research show that a metal bellows device holds promise as a landing shock absorber and launch actuator to extend the range of hopper spacecraft.
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Date Issued: 2015
Identifier: CFE0006015, ucf:51022
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006015

Title: Characteristics of Hydrogel-Wetted Thin Films.
Creator: Owens, James, Putnam, Shawn, Chow, Louis, Xu, Yunjun, University of Central Florida
Abstract / Description: The meniscus region of a thin film is known to have high heat transfer properties due to high evaporation rates and activation of latent heat. The region known as the thin film meniscus (?_film(
Show moreThe meniscus region of a thin film is known to have high heat transfer properties due to high evaporation rates and activation of latent heat. The region known as the thin film meniscus (?_film(<)2 (&)#181;m ) can account for more than half of the total heat transfer of a droplet or film. This study focuses on the potential elongation and curvature amplification of the thin film meniscus region by the implementation of a layer of high hydrogen bonding (hydrogel) film on which the liquid meniscus is built. Forced wetting via liquid propagation though this hydrogel layer in the radial direction increases the surface area of the film. By analyzing the mass flux of liquid lost through evaporation and using both spectroscopic and optical methods to obtain the curvature of the film, relationships between hydrogel thickness and the resulting mass flux were made. Isothermal and steady state assumptions were used to relate hydrogel thickness layers to meniscus curvature, evaporative mass flux, and overall heat transfer coefficients. The experimental results demonstrate, that steady state conditions are achievable with small percentage change in film profile over time. These results are promising toward the addition of the hydrogel coatings and further advancements in heat piping and high heat flux cooling systems for micro electronic devices.
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Date Issued: 2017
Identifier: CFE0006634, ucf:51257
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006634

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: Implementation of Optical Interferometry and Spectral Reflectometry for High Fidelity Thin Film Measurements.
Creator: Arends-Rodriguez, Armando, Putnam, Shawn, Chow, Louis, Kauffman, Jeffrey, University of Central Florida
Abstract / Description: An in-house reflectometer/interferometer has been built to investigate the varying curvature and thickness profiles in the contact line region of air, acetone, iso-octane, ethanol, and water on various types of substrates. Light intensity measurements were obtained using our reflectometer/interferomter and then analyzed in MATLAB to produce thickness and curvature profiles. The apparatus is based on the principle of a reflectometer, consisting of different optical elements, probe, light...
Show moreAn in-house reflectometer/interferometer has been built to investigate the varying curvature and thickness profiles in the contact line region of air, acetone, iso-octane, ethanol, and water on various types of substrates. Light intensity measurements were obtained using our reflectometer/interferomter and then analyzed in MATLAB to produce thickness and curvature profiles. The apparatus is based on the principle of a reflectometer, consisting of different optical elements, probe, light source, and spectrometer. Our reflectometer/interferomter takes measurements in the UV-Vis-IR range (200nm-1000nm). This range is achieved by using a light source that has both a deuterium light (190nm-800nm), a tungsten halogen light (400nm-1100nm), a Metal-Core Printed Circuit Board LED (800nm-1000nm) and a Metal-Core Printed Circuit board cold white LED (400nm-800nm, 6500 K). A UV-VIS-IR spectrometer reads the light response after light is focused on the region of interest. Then a CCD camera (2448x2048) records the profiles for image analyzing interferometry. The readings were then validated based on results in the literature and studies with cylindrical lens samples.
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Date Issued: 2017
Identifier: CFE0006559, ucf:51328
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006559

Title: Analysis of steady state micro-droplet evaporation to enhance heat dissipation from tiny surfaces.
Creator: Voota, Harish, Putnam, Shawn, Kauffman, Jeffrey, Vasu Sumathi, Subith, University of Central Florida
Abstract / Description: Steady state droplet evaporation experiments are conducted to understand (1) Droplet contact line influence on evaporation rate and (2) Droplet contact angle correlation to evaporation rate. Experiments are performed on a polymer substrate with a moat like trench (laser patterned) to control droplet contact line dynamics. A bottom-up methodology is implemented for droplet formation on the patterned substrate. Droplet evaporation rates on substrate temperatures 22???T_Substrate?70? and contact...
Show moreSteady state droplet evaporation experiments are conducted to understand (1) Droplet contact line influence on evaporation rate and (2) Droplet contact angle correlation to evaporation rate. Experiments are performed on a polymer substrate with a moat like trench (laser patterned) to control droplet contact line dynamics. A bottom-up methodology is implemented for droplet formation on the patterned substrate. Droplet evaporation rates on substrate temperatures 22???T_Substrate?70? and contact angles 80(&)deg;???110(&)deg; are measured. For a pinned microdroplet (CCR), volumetric infuse rate influences droplet contact angle. Results illustrate droplet contact line impact on evaporation rate . Moreover, these results coincide with previously published results and affirm that evaporation rate efficiency reduces with contact line depinning. Additionally, from all the analyzed experimental cases, evaporation rate scales proportional to the microdroplet contact angle (i.e. ?_(LG )??). In conclusion, these experiments shed new light on steady state evaporation of a microdroplet and its corresponding observations. Vital research findings can be used to enhance heat dissipation from tiny surfaces.
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Date Issued: 2015
Identifier: CFE0006235, ucf:51067
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006235

Title: Local transient characterization of thermofluid heat transfer coefficient at solid-liquid nano-interfaces.
Creator: Mehrvand, Mehrdad, Putnam, Shawn, Peles, Yoav, Orlovskaya, Nina, Abdolvand, Reza, University of Central Florida
Abstract / Description: The demands for increasingly smaller, more capable, and higher power density technologies in microelectronics, energy, or aerospace systems have heightened the need for new methods to manage and characterize extreme heat fluxes (EHF). Microscale liquid cooling techniques are viewed as a promising solution for removing heat from high heat flux (HHF) systems. However, there have been challenges in physical understanding and predicting local thermal transport at the interface of micro and...
Show moreThe demands for increasingly smaller, more capable, and higher power density technologies in microelectronics, energy, or aerospace systems have heightened the need for new methods to manage and characterize extreme heat fluxes (EHF). Microscale liquid cooling techniques are viewed as a promising solution for removing heat from high heat flux (HHF) systems. However, there have been challenges in physical understanding and predicting local thermal transport at the interface of micro and nanoscale structures/devices due to ballistic effects and complex coupling of mass, momentum, and energy transport at the solid-liquid-vapor interfaces over multiple time and length scales. Moreover, it's challenging to experimentally validate new HHF models due to lack of high resolution techniques and measurements.This dissertation presents the use of a high spatiotemporal and temperature resolution measurement technique, called Time-domain Thermoreflectance (TDTR). TDTR is used to characterize the local heat transfer coefficient (HTC) of a water-cooled rectangular microchannel in a combined hot-spot heating and sub-cooled channel-flow configuration. Studies focused on room temperature, syringe-pumped single-and two-phase water flow in a ?480 ?m hydraulic diameter microchannel, where the TDTR pump heating laser induces local heat fluxes of ?0.5-2.5 KW/cm2 in the center of the microchannel on the surface of a 60-80 nm metal or alloy thin film transducer with hot-spot diameters of ?7-10 ?m. In the single-phase part, a differential measurement approach is developed by applying anisotropic version of the TDTR to predict local HTC using the measured voltage ratio parameter, and then fitting data to a thermal model for layered materials and interfaces. It's shown that thermal effusivity distribution of the water coolant over the hot-spot is correlated to the local HTC, where both the stagnant fluid (i.e., conduction and natural convection) and flowing fluid (i.e., forced convection) contributions are decoupled from each other. Measurements of the local enhancement in the HTC over the hot-spot are in good agreement with established Nusselt number correlations. For example, flow cooling results using a Ti metal wall support a maximum HTC enhancement via forced convection of ?1060(&)#177;190 kW/m2?K, where the well-established Nusselt number correlations predict ?900(&)#177;150 kW/m2?K.In the two-phase part, pump-probe beams are first used to construct the local pool and flow boiling curves at different heat fluxes and hot spot temperatures as a function of HTC enhancement. At a same heat flux level, it's observed that fluid flow enhances HTC by shifting heat transfer mechanism (or flow regime) from film boiling to nucleate boiling. Based on observations, it's hypothesized that beyond an EHF flow may reduce the bubble size and increase evaporation at the liquid-vapor interface on three-phase contact line, but it's unable to rewet and cool down the dry spot at the center due to the EHF. In the last part of two-phase experiments, transient measurements are performed at a specific heat flux to obtain thermal temporal fluctuations and HTC of a single bubble boiling and nucleation during its ebullition cycle. The total laser power is chosen to be between the minimum required to start subcooled nucleation and CHF of the pool boiling. This range is critical since within 10% change in heating flux, flow can have dramatic effect on HTC. Whenever the flow gets closer to the dry spot and passes through it (receding or advancing) HTC increases suddenly. This means that for very hot surfaces (or regions of wall dry-out), continuous and small bubbles on the order of thermal diffusion time and dry spot length scales respectively could be a reliable high heat flux cooling solution. This could be achieved by controlling the bubble size and frequency through geometry, surface structure and properties, and fluid's thermos-fluid properties.
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Date Issued: 2017
Identifier: CFE0006765, ucf:51832
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006765

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.
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Date Issued: 2015
Identifier: CFE0005903, ucf:50856
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005903

Reflectometry (2)	+ -
2d materials (1)	+ -
Boiling Dynamics (1)	+ -
Combined-Cycle Power Plant (1)	+ -
DOE (1)	+ -

Diffusion models (1)	+ -
Droplet (1)	+ -
Droplet constant contact angle (1)	+ -
Droplet constant contact radius (1)	+ -
Droplet evaporation (1)	+ -
Evaporation (1)	+ -
Evaporation rate to contact line correlation (1)	+ -
Faraday effect (1)	+ -
Heat Recovery Steam Generator (1)	+ -
Heat Transfer (1)	+ -
Heat Transfer Coefficient (1)	+ -
Heat flux (1)	+ -
Heat-transfer (1)	+ -
Hydrogel (1)	+ -
Interferometry (1)	+ -
Meniscus (1)	+ -
Microchannel (1)	+ -
Nanofilms (1)	+ -
Particles (1)	+ -
Solid-Liquid Interface (1)	+ -
Steady state droplet evaporation (1)	+ -
TDTR (1)	+ -
Thermodynamic Modeling and Simulation (1)	+ -
Thin-film (1)	+ -
Wicking Structures (1)	+ -

ETD Collection (9)	+ -
Honors Collection (2)	+ -

Putnam, Shawn (11)	+ -
University of Central Florida (11)	+ -
Kauffman, Jeffrey (3)	+ -
Chow, Louis (2)	+ -
Deng, Weiwei (2)	+ -

Gleason, Kevin (2)	+ -
Peles, Yoav (2)	+ -
Abdolvand, Reza (1)	+ -
Akturk, Ali (1)	+ -
Arends-Rodriguez, Armando (1)	+ -
Bhattacharya, Samik (1)	+ -
Caesar, Andres (1)	+ -
Chen, Ruey-Hung (1)	+ -
Das, Tuhin (1)	+ -
Ismayilov, Fuad (1)	+ -
Kassab, Alain (1)	+ -
Mehrvand, Mehrdad (1)	+ -
Murdock, Richard (1)	+ -
Orlovskaya, Nina (1)	+ -
Owens, James (1)	+ -
Raghavan, Seetha (1)	+ -
Trautwein, John (1)	+ -
Vasu Sumathi, Subith (1)	+ -
Voota, Harish (1)	+ -
Wei, Yan (1)	+ -
Wu, Thomas (1)	+ -
Xu, Yunjun (1)	+ -
Zhai, Lei (1)	+ -

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