ASU Electronic Theses and Dissertations
This collection includes most of the ASU Theses and Dissertations from 2011 to present. ASU Theses and Dissertations are available in downloadable PDF format; however, a small percentage of items are under embargo. Information about the dissertations/theses includes degree information, committee members, an abstract, supporting data or media.
In addition to the electronic theses found in the ASU Digital Repository, ASU Theses and Dissertations can be found in the ASU Library Catalog.
Dissertations and Theses granted by Arizona State University are archived and made available through a joint effort of the ASU Graduate College and the ASU Libraries. For more information or questions about this collection contact or visit the Digital Repository ETD Library Guide or contact the ASU Graduate College at gradformat@asu.edu.
Filtering by
- Creators: Zhang, Wenlong
- Creators: Rykaczewski, Konrad
ure of merit (zT) due to quantum connement eects. Improving the eciency of
thermoelectric devices allows for the development of better, more economical waste
heat recovery systems. Such systems may be used as bottoming or co-generation
cycles in conjunction with conventional power cycles to recover some of the wasted
heat. Thermal conductivity measurement systems are an important part of the char-
acterization processes of thermoelectric materials. These systems must possess the
capability of accurately measuring the thermal conductivity of both bulk and thin-lm
samples at dierent ambient temperatures.
This paper discusses the construction, validation, and improvement of a thermal
conductivity measurement platform based on the 3-Omega technique. Room temperature
measurements of thermal conductivity done on control samples with known properties
such as undoped bulk silicon (Si), bulk gallium arsenide (GaAs), and silicon dioxide
(SiO2) thin lms yielded 150 W=m􀀀K, 50 W=m􀀀K, and 1:46 W=m􀀀K respectively.
These quantities were all within 8% of literature values. In addition, the thermal
conductivity of bulk SiO2 was measured as a function of temperature in a Helium-
4 cryostat from 75K to 250K. The results showed good agreement with literature
values that all fell within the error range of each measurement. The uncertainty in
the measurements ranged from 19% at 75K to 30% at 250K. Finally, the system
was used to measure the room temperature thermal conductivity of a nanocomposite
composed of cadmium selenide, CdSe, nanocrystals in an indium selenide, In2Se3,
matrix as a function of the concentration of In2Se3. The observed trend was in
qualitative agreement with the expected behavior.
i
Next, a fundamental study is presented on the phase stability and solid-liquid transformation of metallic (In, Sn and Bi) colloidal nanocrystals. Although the phase change of nanoparticles has been a long-standing research topic, the melting behavior of colloidal nanocrytstals is largely unexplored. In addition, this study is of practical importance to nanocrystal-based applications that operate at elevated temperatures. Embedding colloidal nanocrystals into thermally-stable polymer matrices allows preserving nanocrystal size throughout melt-freeze cycles, and therefore enabling observation of stable melting features. Size-dependent melting temperature, melting enthalpy and melting entropy have all been measured and discussed.
In the next two chapters, focus has been switched to developing colloidal nanocrystal-based phase change composites for thermal energy storage applications. In Chapter 4, a polymer matrix phase change nanocomposite has been created. In this composite, the melting temperature and energy density could be independently controlled by tuning nanocrystal diameter and volume fractions. In Chapter 5, a solution-phase synthesis on metal matrix-metal nanocrytal composite is presented. This approach enables excellent morphological control over nanocrystals and demonstrated a phase change composite with a thermal conductivity 2 - 3 orders of magnitude greater than typical phase change materials, such as organics and molten salts.
In this research, the additive manufacturing technology and the heat exchanger design are explored to find a unique solution to improve the efficiency of heat exchangers. This includes creating a Triply Periodic Minimal Surface (TPMS) geometry, Schwarz-D in this case, using Mathematica with a flexibility to control the cell size of the models generated. This model is then encased in a closed cubical surface with manifolds for fluid inlets and outlets before 3D printed using the polymer nylon for thermal evaluation.
In the extent of this study, the heat exchanger developed is experimentally evaluated. The data obtained are used to derive a relationship between the heat transfer effectiveness and the Number of Transfer Units (NTU).The pressure loss across a fluid channel of the Schwarz D geometry is also studied.
The data presented in this study are part of initial experimental evaluation of 3D printed TPMS heat exchangers.Among heat exchangers with similar performance, the Schwarz D geometry is 32% smaller compared to a shell-and-tube heat exchanger.
that would otherwise exist only on paper. An excellent example of such designs
are the Triply Periodic Minimal Surface (TPMS) structures like Schwarz D, Schwarz
P, Gyroid, etc. These structures are self-sustaining, i.e. they require minimal supports
or no supports at all when 3D printed. These structures exist in stable form in
nature, like butterfly wings are made of Gyroids. Automotive and aerospace industry
have a growing demand for strong and light structures, which can be solved using
TPMS models. In this research we will try and understand some of the properties of
these Triply Periodic Minimal Surface (TPMS) structures and see how they perform
in comparison to the conventional models. The research was concentrated on the
mechanical, thermal and fluid flow properties of the Schwarz D, Gyroid and Spherical
Gyroid Triply Periodic Minimal Surface (TPMS) models in particular, other Triply
Periodic Minimal Surface (TPMS) models were not considered. A detailed finite
element analysis was performed on the mechanical and thermal properties using ANSYS
19.2 and the flow properties were analyzed using ANSYS Fluent under different
conditions.
One of the ways in which we can improve the efficiency of heat exchangers is by applying ultrasonic energy to a heat exchanger. This research explores the possibility of introducing the external input of ultrasonic energy to increase the efficiency of the heat exchanger. This increase in efficiency can be estimated by calculating the parameters important for the characterization of a heat exchanger, which are effectiveness (ε) and overall heat transfer coefficient (U). These parameters are calculated for both the non-ultrasound and ultrasound conditions in the heat exchanger.
This a preliminary study of ultrasound and its effect on a conventional shell-and-coil heat exchanger. From the data obtained it can be inferred that the increase in effectiveness and overall heat transfer coefficient upon the application of ultrasound is 1% and 6.22% respectively.
The experience gained is the understanding of how a cost function of a system works, including the tracking error, speed of the system, the robot’s effort, and the human’s effort. Also, this two-agent system, results into a two-agent adaptive impedance model with an input for each agent of the system. This leads to a nontraditional linear quadratic regulator (LQR), that must be separated and then added together. Thus, creating a traditional LQR. This new experience can be used in the future to help build better safety protocols on manufacturing robots. In the future the knowledge learned from this research could be used to develop technologies for a robot to allow to adapt to help counteract human error.