Date of Graduation

12-2011

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering (MSCE)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

Selvam, R. Panneer

Committee Member

Hale, W. Micah

Second Committee Member

Heymsfield, Ernest

Keywords

Applied sciences; Concrete; High temperatures; Modeling; Molten solar salt; Thermocline

Abstract

The past couple of decades have shown a concern when considering the way the world obtains its power. The focus has been switching from fossil fuels that have been used for hundreds of years to renewable energy sources, such as the sun. Solar energy is readily and infinitely available for harnessing. One problem with solar energy, though, is its inability to be used during the night time and during cloud covered weather. A solution to this problem is the use of energy storage mechanisms. For solar plants that use solar thermal energy (concentrating solar power plants), thermal energy storage (TES) has been the focus. Single tank thermocline TES systems have been used on a limited basis with packed beds as the filler material to lower costs compared to traditional two tank storage options. In this type of system, a thermal gradient is maintained inside of the tank in order to keep the hot and the cold fluid within the same tank without thermal mixing. The problem with packed beds is that settling of the filler material during thermal cycling causes thermal ratcheting on the tank from increased wall hoop stresses. This could ultimately cause a catastrophic failure of the tank wall. This research focuses on concrete being used in a thermocline type TES system with nitrate solar salt as the heat transfer fluid. The goal of this research is to use modeling based on finite difference method to design a structured concrete thermocline TES system. A structure concrete thermocline replaces the packed bed filler material with concrete structures, eliminating the issue of thermal ratcheting. Also this research covers testing of proprietary concrete mixtures designed at the University of Arkansas to determine their compatibility with nitrate solar salt heat transfer fluid at an operating temperature of 585° C. Discharge efficiencies were found for structured concrete filler material geometries that reached a maximum of 65.59 percent. Proprietary mixes created by the University of Arkansas were found to be adequate for long term use in the solar salt environment.

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