Theses and Dissertations
This collection includes both ASU Theses and Dissertations, submitted by graduate students, and the Barrett, Honors College theses submitted by undergraduate students.
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- Creators: Phelan, Patrick
Description
Understanding and predicting climate changes at the urban scale have been an important yet challenging problem in environmental engineering. The lack of reliable long-term observations at the urban scale makes it difficult to even assess past climate changes. Numerical modeling plays an important role in filling the gap of observation and predicting future changes. Numerical studies on the climatic effect of desert urbanization have focused on basic meteorological fields such as temperature and wind. For desert cities, urban expansion can lead to substantial changes in the local production of wind-blown dust, which have implications for air quality and public health. This study expands the existing framework of numerical simulation for desert urbanization to include the computation of dust generation related to urban land-use changes. This is accomplished by connecting a suite of numerical models, including a meso-scale meteorological model, a land-surface model, an urban canopy model, and a turbulence model, to produce the key parameters that control the surface fluxes of wind-blown dust. Those models generate the near-surface turbulence intensity, soil moisture, and land-surface properties, which are used to determine the dust fluxes from a set of laboratory-based empirical formulas. This framework is applied to a series of simulations for the desert city of Erbil across a period of rapid urbanization. The changes in surface dust fluxes associated with urbanization are quantified. An analysis of the model output further reveals the dependence of surface dust fluxes on local meteorological conditions. Future applications of the models to environmental prediction are discussed.
ContributorsTahir, Sherzad Tahseen (Author) / Huang, Huei-Ping (Thesis advisor) / Phelan, Patrick (Committee member) / Herrmann, Marcus (Committee member) / Chen, Kangping (Committee member) / Clarke, Amanda (Committee member) / Arizona State University (Publisher)
Created2019
Description
Durable, cost-effective, and environmentally friendly anti-icing methods are desired to reduce the icing hazard in many different industrial areas including transportation systems, power plants, power transmission, as well as offshore oil and gas production. In contrast to traditional passive anti-icing surfaces, this thesis work introduces an anti-icing coating that responds to different icing conditions by releasing an antifreeze liquid. It consists of an outer porous superhydrophobic epidermis and a wick-like underlying dermis that is infused with the antifreeze liquid. This bi-layer coating prevents accumulation of frost, freezing fog, and freezing rain, while conventional anti-icing surfaces typically work only in one of these conditions. The bi-layer coating also delays condensation on the exterior surface at least ten times longer than identical system without antifreeze.
It is demonstrated that the significant delay in condensation onset is due to the integral humidity sink effect posed by the hygroscopic antifreeze liquid infused in the porous structure. This effect significantly alters the water vapor concentration field at the coating surface, which delays nucleation of drops and ice. It was demonstrated that with a proper design of the environmental chamber the size of the region of inhibited condensation and condensation frosting around an isolated pore, as well as periodically spaced pores, filled by propylene glycol can be quantitatively predicted from quasi-steady state water vapor concentration field. Theoretical analysis and experiments revealed that the inhibition of nucleation is governed by only two non-dimensional geometrical parameters: the pore size relative to the unit cell size and the ratio of the unit cell size to the thickness of the boundary layer. It is demonstrated that by switching the size of the pores from millimeters to nanometers, a dramatic depression of the nucleation onset temperature, as well as significantly greater delay in nucleation onset can be achieved.
It is demonstrated that the significant delay in condensation onset is due to the integral humidity sink effect posed by the hygroscopic antifreeze liquid infused in the porous structure. This effect significantly alters the water vapor concentration field at the coating surface, which delays nucleation of drops and ice. It was demonstrated that with a proper design of the environmental chamber the size of the region of inhibited condensation and condensation frosting around an isolated pore, as well as periodically spaced pores, filled by propylene glycol can be quantitatively predicted from quasi-steady state water vapor concentration field. Theoretical analysis and experiments revealed that the inhibition of nucleation is governed by only two non-dimensional geometrical parameters: the pore size relative to the unit cell size and the ratio of the unit cell size to the thickness of the boundary layer. It is demonstrated that by switching the size of the pores from millimeters to nanometers, a dramatic depression of the nucleation onset temperature, as well as significantly greater delay in nucleation onset can be achieved.
ContributorsSun, Xiaoda (Author) / Rykaczewski, Konrad (Thesis advisor) / Lin, Jerry (Committee member) / Phelan, Patrick (Committee member) / Wang, Robert (Committee member) / Herrmann, Marcus (Committee member) / Wang, Liping (Committee member) / Arizona State University (Publisher)
Created2017
Description
Many defense, healthcare, and energy applications can benefit from the development of surfaces that easily shed droplets of liquids of interest. Desired wetting properties are typically achieved via altering the surface chemistry or topography or both through surface engineering. Despite many recent advancements, materials modified only on their exterior are still prone to physical degradation and lack durability. In contrast to surface engineering, this thesis focuses on altering the bulk composition and the interior of a material to tune how an exterior surface would interact with liquids. Fundamental and applied aspects of engineering of two material systems with low contact angle hysteresis (i.e. ability to easily shed droplets) are explained. First, water-shedding metal matrix hydrophobic nanoparticle composites with high thermal conductivity for steam condensation rate enhancement are discussed. Despite having static contact angle <90° (not hydrophobic), sustained dropwise steam condensation can be achieved at the exterior surface of the composite due to low contact angle hysteresis (CAH). In order to explain this observation, the effect of varying the length scale of surface wetting heterogeneity over three orders of magnitude on the value of CAH was experimentally investigated. This study revealed that the CAH value is primarily governed by the pinning length which in turn depends on the length scale of wetting heterogeneity. Modifying the heterogeneity size ultimately leads to near isotropic wettability for surfaces with highly anisotropic nanoscale chemical heterogeneities. Next, development of lubricant-swollen polymeric omniphobic protective gear for defense and healthcare applications is described. Specifically, it is shown that the robust and durable protective gear can be made from polymeric material fully saturated with lubricant that can shed all liquids irrespective of their surface tensions even after multiple contact incidences with the foreign objects. Further, a couple of schemes are proposed to improve the rate of lubrication and replenishment of lubricant as well as reduce the total amount of lubricant required in making the polymeric protective gear omniphobic. Overall, this research aims to understand the underlying physics of dynamic surface-liquid interaction and provides simple scalable route to fabricate better materials for condensers and omniphobic protective gear.
ContributorsDamle, Viraj (Author) / Rykaczewski, Konrad (Thesis advisor) / Phelan, Patrick (Committee member) / Lin, Jerry (Committee member) / Herrmann, Marcus (Committee member) / Wang, Robert (Committee member) / Wang, Liping (Committee member) / Arizona State University (Publisher)
Created2017
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
Description
Gas Dynamic Virtual Nozzles (GDVN) produce microscopic flow-focused liquid jets and are widely used for sample delivery in serial femtosecond crystallography (SFX) and time-resolved solution scattering. Recently, 2-photon polymerization (2PP) made it possible to produce 3D-printed GDVNs with submicron printing resolution. Comparing with hand- fabricated nozzles, reproducibility, and less developing effort, and similarity of the performance of different 3D printed nozzles are among the advantages of using 3D printing techniques to develop GDVN’s. Submicron printing resolution also makes it possible to easily improve GDVN performance by optimizing the design of nozzles. In this study, 3D printed nozzles were developed to achieve low liquid and gas flow rates and high liquid jet velocities. A double-pulsed nanosecond laser imaging system was used to perform Particle Tracking Velocimetry (PTV) in order to determine jet velocities and assess jet stability/reproducibility. The testing results of pure water jets focused with He sheath gas showed that some designs can easily achieve stable liquid jets with velocities of more than 80 m/s, with pure water flowing at 3 microliters/min, and helium sheath gas flowing at less than 5 mg/min respectively. A numerical simulation pipeline was also used to characterize the performance of different 3D printed GDVNs. The results highlight the potential of making reproducible GDVNs with minimum fabrication effort, that can meet the requirements of present and future SFX and time-resolved solution scattering research.
ContributorsNazari, Reza (Author) / Adrian, Ronald (Thesis advisor) / Kirian, Richard (Thesis advisor) / Herrmann, Marcus (Committee member) / Phelan, Patrick (Committee member) / Weierstall, Uwe (Committee member) / Arizona State University (Publisher)
Created2020