Date of Award

6-2017

Degree Name

Doctor of Philosophy

Department

Mechanical and Aerospace Engineering

First Advisor

Dr. HoSung Lee

Second Advisor

Dr. Chris Cho

Third Advisor

Dr. Kristina Lemmer

Fourth Advisor

Dr. Abraham Engeda

Abstract

Fossil fuels are the major energy sources that are used in the world today, even though these kinds of sources create significant and harmful impacts on our health, our environment, and our climate. Another disadvantage of fossil fuels is that they often cost more than other forms of energy, such as solar energy. Photovoltaic cells and solar thermal generation are types of renewable energy that promote a clean atmosphere and reduce the cost of energy. Photovoltaic solar cells and solar thermal generation are the basic techniques used to convert sunlight into electricity.

This study explores thermoelectrics as a viable option for small-scale solar thermal applications. Thermoelectric technology is based on the Seebeck effect, which states that a voltage is induced when a temperature gradient is applied to the junctions of two differing materials. In the case of a solar thermoelectric generator (STEG), the hot side is the solar absorber, and the cold side is the heat sink. This research proposes to analyze, validate, simulate, optimize, and design a prototype STEG in order to increase efficiency. The intent is to further develop solar thermoelectric generators as a viable and productive energy source that limits pollution and reduces the cost of energy production.

Best practice review in the field of STEGs determined that typical efficiencies are relatively low compared to other renewable energy devices. Many research efforts today explore increasing overall performance using material optimization, experimentation, analytical approaches, and numerical simulations of an STEG system. The spectral analyses for thermal radiation, glass, and solar absorbers are studied in order to predict behavior of the thermal properties, such as absorptivity, transmissivity, reflectivity, and emissivity. The analytical approach for the thermoelectric generator includes testing performance of the device using ideal and exact solutions, as well as a thermodynamic property called the “compatibility factor”.

A recent empirical study (Kraemer, 2011) on the solar thermoelectric generator reported a high efficiency performance of 4.6%. The system had a vacuum glass enclosure, a flat panel (absorber), thermoelectric generator and water circulation for the cold side. The theoretical and numerical approach of this current study validated the experimental results from Kraemer's study to a high degree.

The numerical simulation process utilizes a two-stage approach in ANSYS software for Fluent and Thermal-Electric systems. The solar load model technique uses solar radiation under AM 1.5G conditions in Fluent. This analytical model applies Dr. HoSung Lee’s theory of optimal design to improve performance of the STEG system by using dimensionless parameters.

Considering all of the above studies and works, a new and optimum design of a STEG has been developed for attaining an increased efficiency of 21.6 %. The new design consists of three cascaded thermoelectric materials. In addition, it includes two glass panes, a selective solar absorber, two radiation shields, and forced air cooling system. The design is modeled theoretically and numerically using ANSYS software.

Access Setting

Dissertation-Abstract Only

Restricted to Campus until

6-2027

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