Graduation Semester and Year

2015

Language

English

Document Type

Thesis

Degree Name

Master of Science in Aerospace Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Donghyun Shin

Abstract

Recent studies have shown that using a single fluid for Heat Transfer and Thermal Energy Storage, improves the working and efficiency of a CSP. It improves the conversion efficiency (thermal energy to electrical) and also reduce the thermal losses due to heat exchangers by eliminating them. Other methods of storage are thermo chemical TES or phase change TES, but they require heat exchanger between HTF and TES medium, due to which the thermal losses between them are significant. CSP works on a conventional thermodynamic cycle (Rankine Cycle, Brayton Cycle) indicating that higher operating temperature are required to achieve higher efficiency. Higher temperature would also help us to use these materials in other applications like Oil refineries, molten salt reactors. However, lack of available fluids at higher temperatures are a hindrance towards raising the temperature. Conventional materials used as storage material are not thermally stable at higher temperature. The critical temperature of water 374.15°C at 221.2 bar and organic storage fluid such as oil, ethylene glycol well below 400°C. Molten salts can be an effective alternate material due to its stability at higher temperatures and cheap availability. The upcoming solar thermal plants use eutectic fluid system (eg solar salt, NaNO3-KNO3) as TES material at higher temperature. This can raise the operating temperature from 300°C to 500°C as they start to decompose around that temperature. In order to further increase the operating temperature to around 700°C, we need to look out for other materials. Alkali chlorides provide a suitable alternative as they are stable at this temperature. Along with low vapor pressure and good heat transfer characteristics, we can use them to store energy at higher temperature. The disadvantage of using them at higher temperature are its corrosion effect and its poor thermal properties. At higher temperatures ceramic or high-temperature alloys should be used as the structure materials due to the creep of stainless steel and therefore corrosion may not be an issue. Thermal properties can be enhanced by doping the base salt with nano particles. In this study, we have developed a binary eutectic chloride mixture (Lithium Chloride and Potassium Chloride) with addition of silicon oxide nanoparticles (2% weight addition) which show around 15% enhancement in its thermal heat capacity. This study would help in commercialization of these HTF and also effectively reduce the cost of production of electricity.

Disciplines

Aerospace Engineering | Engineering | Mechanical Engineering

Comments

Degree granted by The University of Texas at Arlington

Download

Share

COinS