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Description
Many physical phenomena and industrial applications involve multiphase fluid flows and hence it is of high importance to be able to simulate various aspects of these flows accurately. The Dynamic Contact Angles (DCA) and the contact lines at the wall boundaries are a couple of such important aspects. In the past few decades, many mathematical models were developed for predicting the contact angles of the inter-face with the wall boundary under various flow conditions. These models are used to incorporate the physics of DCA and contact line motion in numerical simulations using various interface capturing/tracking techniques. In the current thesis, a simple approach to incorporate the static and dynamic contact angle boundary conditions using the level set method is developed and implemented in multiphase CFD codes, LIT (Level set Interface Tracking) (Herrmann (2008)) and NGA (flow solver) (Desjardins et al (2008)). Various DCA models and associated boundary conditions are reviewed. In addition, numerical aspects such as the occurrence of a stress singularity at the contact lines and grid convergence of macroscopic interface shape are dealt with in the context of the level set approach.
ContributorsPendota, Premchand (Author) / Herrmann, Marcus (Thesis advisor) / Rykaczewski, Konrad (Committee member) / Chen, Kangping (Committee member) / Arizona State University (Publisher)
Created2015
Description
The proposed research mainly focuses on employing tunable materials to achieve dynamic control of radiative heat transfer in both far and near fields for thermal management. Vanadium dioxide (VO2), which undergoes a phase transition from insulator to metal at the temperature of 341 K, is one tunable material being applied. The other one is graphene, whose optical properties can be tuned by chemical potential through external bias or chemical doping.
In the far field, a VO2-based metamaterial thermal emitter with switchable emittance in the mid-infrared has been theoretically studied. When VO2 is in the insulating phase, high emittance is observed at the resonance frequency of magnetic polaritons (MPs), while the structure becomes highly reflective when VO2 turns metallic. A VO2-based thermal emitter with tunable emittance is also demonstrated due to the excitation of MP at different resonance frequencies when VO2 changes phase. Moreover, an infrared thermal emitter made of graphene-covered SiC grating could achieve frequency-tunable emittance peak via the change of the graphene chemical potential.
In the near field, a radiation-based thermal rectifier is constructed by investigating radiative transfer between VO2 and SiO2 separated by nanometer vacuum gap distances. Compared to the case where VO2 is set as the emitter at 400 K as a metal, when VO2 is considered as the receiver at 300 K as an insulator, the energy transfer is greatly enhanced due to the strong surface phonon polariton (SPhP) coupling between insulating VO2 and SiO2. A radiation-based thermal switch is also explored by setting VO2 as both the emitter and the receiver. When both VO2 emitter and receiver are at the insulating phase, the switch is at the “on” mode with a much enhanced heat flux due to strong SPhP coupling, while the near-field radiative transfer is greatly suppressed when the emitting VO2 becomes metallic at temperatures higher than 341K during the “off” mode. In addition, an electrically-gated thermal modulator made of graphene covered SiC plates is theoretically studied with modulated radiative transport by varying graphene chemical potential. Moreover, the MP effect on near-field radiative transport has been investigated by spectrally enhancing radiative heat transfer between two metal gratings.
In the far field, a VO2-based metamaterial thermal emitter with switchable emittance in the mid-infrared has been theoretically studied. When VO2 is in the insulating phase, high emittance is observed at the resonance frequency of magnetic polaritons (MPs), while the structure becomes highly reflective when VO2 turns metallic. A VO2-based thermal emitter with tunable emittance is also demonstrated due to the excitation of MP at different resonance frequencies when VO2 changes phase. Moreover, an infrared thermal emitter made of graphene-covered SiC grating could achieve frequency-tunable emittance peak via the change of the graphene chemical potential.
In the near field, a radiation-based thermal rectifier is constructed by investigating radiative transfer between VO2 and SiO2 separated by nanometer vacuum gap distances. Compared to the case where VO2 is set as the emitter at 400 K as a metal, when VO2 is considered as the receiver at 300 K as an insulator, the energy transfer is greatly enhanced due to the strong surface phonon polariton (SPhP) coupling between insulating VO2 and SiO2. A radiation-based thermal switch is also explored by setting VO2 as both the emitter and the receiver. When both VO2 emitter and receiver are at the insulating phase, the switch is at the “on” mode with a much enhanced heat flux due to strong SPhP coupling, while the near-field radiative transfer is greatly suppressed when the emitting VO2 becomes metallic at temperatures higher than 341K during the “off” mode. In addition, an electrically-gated thermal modulator made of graphene covered SiC plates is theoretically studied with modulated radiative transport by varying graphene chemical potential. Moreover, the MP effect on near-field radiative transport has been investigated by spectrally enhancing radiative heat transfer between two metal gratings.
ContributorsYang, Yue (Author) / Wang, Liping (Thesis advisor) / Phelan, Patrick (Committee member) / Wang, Robert (Committee member) / Tongay, Sefaattin (Committee member) / Rykaczewski, Konrad (Committee member) / Arizona State University (Publisher)
Created2016
Description
This thesis gives a detailed design process for a pulsed type thruster. The thrust stand designed in this paper is for a Pulsed Plasma Thruster built by Sun Devil Satellite Laboratory, a student organization at Arizona State University. The thrust stand uses a torsional beam rotating to record displacement. This information, along with impulse-momentum theorem is applied to find the impulse bit of the thruster, which varies largely from other designs which focus on using the natural dynamics their fixtures. The target impulse to record on this fixture was estimated to be 275 μN-s of impulse. Through calibration and experimentation, the fixture is capable of recording an impulse of 332 μN-s ± 14.81 μN-s, close to the target impulse. The error due to noise was characterized and evaluated to be under 5% which is deemed to be acceptable.
ContributorsVerbin, Andrew Joseph (Author) / Takahashi, Timothy T (Thesis advisor) / White, Daniel B (Thesis advisor) / Rykaczewski, Konrad (Committee member) / Arizona State University (Publisher)
Created2017
Description
Advancements in thermal interface materials (TIMs) allows for the creation of new and more powerful electronics as they increase the heat transfer from the component to the heat sink. Current industrial options provide decent heat transfer, but the creation of TIMs with higher thermal conductivities is needed. In addition, if these TIMs are elastic in nature, their effectiveness can greatly increase as they can deal with changing interfaces without degradation of their properties. The research performed delves into this idea, creating elastic TIMs using liquid metal (LM), in this case galinstan, along with other matrix particles embedded in Polydimethylsiloxane (PDMS) to create an easy to use, relatively inexpensive, thermally conductive, but electrically insulative, pad with increased thermal conductivity from industrial solutions.
The pads were created using varying amounts of LM and matrix materials ranging from copper microspheres to diamond powder mixed into PDMS using a high-speed mixer. The material was then cast into molds and cured to create the pads. Once the pads were created, the difficulty came in quantifying their thermal properties. A stepped bar apparatus (SBA) following ASTM D5470 was created to measure the thermal resistance of the pads but it was determined that thermal conductivity was a more usable metric of the pads’ performance. This meant that the pad’s in-situ thickness was needed during testing, prompting the installation of a linear encoder to measure the thickness. The design and analysis of the necessary modification and proposed future design is further detailed in the following paper.
The pads were created using varying amounts of LM and matrix materials ranging from copper microspheres to diamond powder mixed into PDMS using a high-speed mixer. The material was then cast into molds and cured to create the pads. Once the pads were created, the difficulty came in quantifying their thermal properties. A stepped bar apparatus (SBA) following ASTM D5470 was created to measure the thermal resistance of the pads but it was determined that thermal conductivity was a more usable metric of the pads’ performance. This meant that the pad’s in-situ thickness was needed during testing, prompting the installation of a linear encoder to measure the thickness. The design and analysis of the necessary modification and proposed future design is further detailed in the following paper.
ContributorsKemme, Nicholas (Author) / Rykaczewski, Konrad (Thesis advisor) / Wang, Robert (Thesis advisor) / Wang, Liping (Committee member) / Arizona State University (Publisher)
Created2017
Description
District heating plays an important role in improving energy efficiency and providing thermal heat to buildings. Instead of using water as an energy carrier to transport sensible heat, this dissertation explores the use of liquid-phase thermochemical reactions for district heating as well as thermal storage. Chapters 2 and 3 present thermodynamic and design analyses for the proposed district heating system. Chapter 4 models the use of liquid-phase thermochemical reactions for on-site solar thermal storage. In brief, the proposed district heating system uses liquid-phase thermochemical reactions to transport thermal energy from a heat source to a heat sink. The separation ensures that the stored thermochemical heat can be stored indefinitely and/or transported long distances. The reactant molecules are then pumped over long distances to the heat sink, where they are combined in an exothermic reaction to provide heat. The product of the exothermic reaction is then pumped back to the heat source for re-use. The key evaluation parameter is the system efficiency.
The results demonstrate that with heat recovery, the system efficiency can be up to 77% when the sink temperature equals 25 C. The results also indicate that the appropriate chemical reaction candidates should have large reaction enthalpy and small reaction entropy. Further, the design analyses of two district heating systems, Direct District Heating (DDH) system and Indirect District Heating (IDH) system using the solvated case shows that the critical distance is 106m. When the distance is shorter than 1000,000m, the factors related to the chemical reaction at the user side and factors related to the separation process are important for the DDH system. When the distance is longer than 106m, the factors related to the fluid mechanic become more important. Because the substation of the IDH system degrades the quality of the energy, when the distance is shorter than 106m, the efficiency of the substation is significant. Lastly, I create models for on-site solar thermal storage systems using liquid-phase thermochemical reactions and hot water. The analysis shows that the thermochemical reaction is more competitive for long-duration storage applications. However, the heat recovery added to the thermochemical thermal storage system cannot help improving solar radiation absorption with high inlet temperature of the solar panel.
ContributorsZhang, Yanan (Author) / Wang, Robert (Thesis advisor) / Milcarek, Ryan (Committee member) / Parrish, Kristen (Committee member) / Phelan, Patrick (Committee member) / Rykaczewski, Konrad (Committee member) / Arizona State University (Publisher)
Created2022
Description
Deformable heat exchangers could provide a multitude of previously untapped advantages ranging from adaptable performance via macroscale, dynamic shape change (akin to dilation/constriction seen in blood vessels) to enhanced heat transfer at thermal interfaces through microscale, surface deformations. So far, making deformable, ‘soft heat exchangers’ (SHXs) has been limited by the low thermal conductivity of materials with suitable mechanical properties. The recent introduction of liquid-metal embedded elastomers by Bartlett et al1 has addressed this need. Specifically, by remaining soft and stretchable despite the addition of filler, these thermally conductive composites provide an ideal material for the new class of “soft thermal systems”, which is introduced in this work. Understanding such thermal systems will be a key element in enabling technology that require high levels of stretchability, such as thermoregulatory garments, soft electronics, wearable electronics, and high-powered robotics. Shape change inherent to SHX operation has the potential to violate many conventional assumptions used in HX design and thus requires the development of new theoretical approaches to predict performance. To create a basis for understanding these devices, this work highlights two sequential studies. First, the effects of transitioning to a surface deformable, SHX under steady state static conditions in the setting of a liquid cooling device for thermoregulation, electronics and robotics applications was explored. In this study, a thermomechanical model was built and validated to predict the thermal performance and a system wide analysis to optimize such devices was carried out. Second, from a more fundamental perspective, the effects of SHXs undergoing transient shape deformation during operation was explored. A phase shift phenomenon in cooling performance dependent on stretch rate, stretch extent and thermal diffusivity was discovered and explained. With the use of a time scale analysis, the extent of quasi-static assumption viability in modeling such systems was quantified and multiple shape modulation regime limits were defined. Finally, nuance considerations and future work of using liquid metal-silicone composites in SHXs were discussed.
ContributorsKotagama, Praveen (Author) / Rykaczewski, Konrad (Thesis advisor) / Wang, Robert (Committee member) / Phelan, Patrick (Committee member) / Herrmann, Marcus (Committee member) / Green, Matthew (Committee member) / Arizona State University (Publisher)
Created2020