Publication Date

2019-08-02

Availability

Embargoed

Embargo Period

2021-08-01

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Mechanical Engineering (Engineering)

Date of Defense

2019-06-21

First Committee Member

Emrah Celik

Second Committee Member

Victoria Coverstone

Third Committee Member

Ryan Karkkainen

Fourth Committee Member

Sedat Ballikaya

Abstract

Thermoelectric systems are energy conversion systems that are able to convert heat to voltage or vice versa, depending on the application. Albeit they lack sufficient efficiency for high scale applications, their silent, environmentally friendly, renewable nature along with no need of maintenance make them promising alternatives to mitigate lost heat. The parameters that need to be taken into consideration when assessing the thermoelectric efficiency are electrical conductivity, thermal conductivity and Seebeck coefficient. Since each variable is coupled to be dependent to another, enhancement of efficiency entails rigorous work that involves nanoengineering. Another drawback of thermoelectric materials is difficulty of fabrication, since conventional fabrication methods offer limited geometries and are considered high-energy methods that are open to production errors. This thesis addresses the aforementioned limitations of thermoelectric materials, by concentrating on introduction of a nano level dopant, carbon quantum dot, and additive manufacturing, which is also known as 3D printing. In this thesis, initially, background information on thermoelectric theory is provided to help understand the addressed issues. Subsequently, a widespread additive manufacturing method, fused filament fabrication is applied on a well-established thermoelectric compound, Bi2Te3 to fabricate intricate structures. Thermoelectric efficiency of these samples were characterized and compared with the previously printed thermoelectric materials in the literature broadly. Later, another highly innovative additive manufacturing method, Selective Laser Sintering is utilized, this time, for a different thermoelectric compound, MnSi1.75 to fabricate disks. Selective laser sintered sample was characterized for thermoelectric performance and microscopy was utilized to corroborate the thermoelectric efficiency, in terms of microstructure and a possible presence of secondary phases. As with the previous topic, the results were compared and contrasted with the previously fabricated thermoelectric materials using both conventional and additive techniques. Final chapter covers examination of a nano dopant, carbon quantum dots (CQDs), for enhancement of efficiency of Bi2Te3. CQD doped, cold-pressed Bi2Te3 disks are characterized to understand the nano effect of the CQD dopant, especially for thermal conductivity, which significantly benefits from the presence of nano particles that trigger phonon scattering effect. The novel method and dopants introduced in this thesis are aimed to help overcome the insufficient efficiency and laborious manufacturing of thermoelectric materials.

Keywords

Thermoelectrics; Additive Manufacturing; Energy Conversion; Nanoengineering

Available for download on Sunday, August 01, 2021

Share

COinS