UC San Diego

According to the Second Law of Thermodynamics, the Carnot engine gives the highest possible efficiency of a power cycle, which is defined as the ratio between the temperature difference between the hot reservoir and the cold reservoir and the hot reservoir temperature. Operating a power cycle at high temperatures is the key to increasing the overall efficiency of a power plant. Concentrating solar power (CSP) is one of the emerging solar-thermal technologies that utilizes the collected concentrated sunlight for generating electricity with zero carbon emission. In the 3rd generation (Gen 3) CSP plants, the target operating temperature is at least 700 oC to achieve higher thermal efficiency and lower levelized cost of electricity (LCOE). In light of this, it is necessary to elucidate our fundamental understanding of the high-temperature materials being used in next-generation CSP plants, including HTFs, thermal energy storage (TES) materials, thermochemical materials, and thermal barrier materials. Chapter 1 is a review of CSP technology and the current research opportunities and challenges at measurement and materials levels. Chapter 2 presents the thermal conductivity measurement of molten salts, including molten nitrate and chloride salts, using novel optical-based thermal characterization, namely, modulated photothermal radiometry (MPR). Chapter 3 presents the first in-situ thermal conductivity measurement for flowing molten salt using MPR. The relative thermal conductivity enhancement due to the forced convection and the heat transfer coefficient (HTC) of flowing molten salts are measured for the first time using MPR. Chapter 4 presents the first in-situ monitoring of thermochemical reactions of hydroxides and perovskites using MPR. The thermal characterization results are correlated to the kinetics of the thermochemical reactions. Chapter 5 presents the surface modification of quartz sand using black spinel oxide nanoparticles for low-cost solar-absorbing and TES applications. Chapter 6 presents the realization of ultra-low thermal conductivity and diffusivity using high-entropy spinel oxide nanoparticles (HESONPs) at high temperatures. Chapter 7 is the conclusion and outlook of the dissertation, providing future research directions related to thermal evaluations of energy devices using non-contact characterization techniques and the design of high-entropy ceramics (HECs) for catalytic, carbon capture, and thermal barrier applications.