Session: 17-05: Symposium Steinfeld - Concentrated solar power and thermal/thermochemical energy storage

Paper Number: 137198

137198 - Characterization of Particulate Media for Solar Thermal Energy Storage and Transport 

Abstract: 

Thermal energy storage (TES) utilizes concentrated solar irradiation as process heat for sensible energy storage, enabling the storage of sunlight for use during non-diurnal periods. Particulate media for heat transfer and TES medium (e.g., sand, sintered bauxite particles, etc.) are appealing in Gen3 in concentrated solar power (CSP) systems due to high thermal capacity, mechanical strength, inertness, and temperature resilience  >1000 °C.  Dense granular flows have been shown as promising heat transfer media due to high thermal absorptivity and durability at elevated temperatures, which further improves the system thermal efficiency. A new suite of particles have been identified, synthesized, and tested with high performing optical an physical properties coupled to durability that potentially reduces the levelized cost of electricity for particle-based CSP. The focus of this work was to investigate black particles (BP) properties, including coefficients of restitution between particles and wall, coefficients of static sliding and static rolling frictions at temperatures up to 800 °C. Understanding particle-particle and particle-wall interactions is crucial for accurately predicting granular flow properties at elevated temperatures and further informing subsequent dense granular flow modeling effort.

Measurements to investigate cofficient of restitution were performed for SiO₂ particles and BP using drop tests. SiO₂ are lowcost translucent particles with effective diameters of 602.6 ± 84.1 μm and low circularity of 0.84 ± 0.03. BP are spinel iron oxide coated SiO­₂ particles with extremely high solar absobtivity, effecitive diameters of  537.42 ± 129.0 μm, and circulatities of 0.83 ± 0.03. The coefficient of restitution was employed to quantify momentum losses between the particles and stainless steel (304) and Inconel 625 plates. Drop tests were performed for particles in air condition at temperatures at ~20 (ambient), 200, 400, 600 and 800 °C with particles velocity vectors before and after impact with metal plates captured using a high-speed camera. Results showed BP having lower coefficient of restitution compared to SiO₂ particles for all temperatures. Significant changes in coefficeint of restitution  as a function of temperature were observed. Particles to Inconel collisions showed the coefficeint of restition generally increased with tempertature up to 600 °C and then drastically decreased from 600 to 800 °C. Particles – stainless steel collisions showed the opposite and undesirable trend with the coefficient of restitution decreasing as temperature increased. Digital microscopy was utilized to elucidate particles and metal plates surface changes in morphologies from thermal cycles, showing slight decrease in surface roughness and increase surface oxidation of Inconel 625 at > 400 °C, likely impacted  the coefficient of resitution changing with surface compostions. The findings suggest mainting operating temperatures of < 800 °C for applications with Inconel 625 to preserve mechanical integrity.  

Particles static friction plays a critical role in Gen3 CSP system as it directly effects flow properties, heat transfer, energy efficiency and mechanical longevity of components. Friction coefficients were measured using similar methods described in previous works.  Static rolling friction was measured using the slip-stick method for four different particles type: (1) BP, (2) SiO₂, (3) Al₂O₃ beads and (4) SiO₂ beads, where the beads features a high circularity of  ≥0.9 and were used for comparison. A translating stage was used to provide motion at 8 μm/s, and an inline force transducer was used to measure the maximum force before slips. Measurements at ambient condition showed BP and SiO₂ particles exibited comparable coefficients of rolling friction. Interaction with Inconel 625 plates yielded higher coefficients of rolling friction compared to stainless steel plates across all particles, likely due to higher surface roughness. Particles circularity played a pivitol role in decreasing the coefficient of rolling friction as higher circular Al₂O₃ beads and SiO₂ beads were significantly lower. Additional measurements of static rolling and sliding friction at elevated temperatures up to 800 °C for particle-particle and particle-Inconel 625 are ongoing to investigate high temperature and thermal cycling impacts.

Presenting Author: Nhu P. Nguyen Georgia Institute of Technology

Presenting Author Biography: Nhu “Ty” Nguyen is a PhD candidate and Graduate Research Assistant in the Woodruff School of Mechanical Engineering at Georgia Institute of Technology. Ty works with Prof. Peter Loutzenhiser at the Solar Fuels and Technology lab, where her work focuses on investigating and characterizing materials for Thermochemical Energy Conversion and Storage.

Authors:

Nhu P. Nguyen Georgia Institute of Technology
Kyu Bum Han Advanced Materials Scientia LLC
Peter G. Loutzenhiser Georgia Institute of Technology