Session: 07-01: Experimental Characterization of Particle Flows

Paper Number: 169985

169985 - Particle Flowability Diagnostic Tool and Evaluation of Hopper Performance for Concentrating Solar Power Relevant Temperatures and Granular Media Including Ratios of Entrained Fines 

Abstract: 

Solid particle media for generation three (Gen3) concentrating solar power (CSP) has desirable characteristics above those of conventional molten salts: stability at higher operation temperatures and self-insulating properties for thermal storage to name two. A primary challenge with the new Gen3 approach is material handling and the associated novel heat exchanger (HX) designs that can accommodate granular media as the heat source. To support the efforts to address these challenges Sandia National Laboratories has expanded on a previously defined [1, 2] experimental procedure. This procedure was used to evaluate the flowability of Gen3 concentrating solar power (CSP) particle components described as hoppers or feeders. Additions to this procedure included custom image processing to estimate a channel-by-channel mass flow estimate through the HX to diagnose a designed hopper’s ability to regulate mass flow through a heat exchanger. Deviations from ideal mass flow rate may lead to temperature differentials outside allowable specification, suboptimal performance, or reduced service life for critical and expensive components in any power cycle.

This diagnostic approach has been applied to two different hopper geometries, a commercially designed mass flow (first in first out) hopper and a custom hopper that has a shorter overall height. These hoppers have been experimentally evaluated for qualitative and quantitative flow differences at three different temperatures (ambient, 500C, and 700C). Further, a single hopper was tested at 700C with three mass ratios of fresh particles and dust/crushed fines (5, 10, and 15% mass). The experimental methodology previously defined has been expanded upon to include custom image processing. This image processing method compared differential images across a fixed analysis window for a raw video to programmatically calculate start of flow, residence time, and estimated the mass flow rate of each channel. A Monte Carlo process estimated errors for the residence time and mass flow estimates.

Between the hoppers, there were a few trends across temperature testing. The commercial mass flow hopper exhibited consistent performance at all temperatures with an apparent difference in residence time temperatures. The custom hopper exhibited some flow maldistribution that was apparent in all tests. Flow through the hopper with different mass ratios of dust varied wildly. Evidence of bridging or ratholing was present as flow stopped altogether at times at the higher two mass ratios. The number of trials conducted limited the conclusions that could be drawn, but the new analysis methods and inclusion of dust/debris/fines into the granular media have value for future work to evaluate the flowability of particles at relevant CSP conditions through critical components. The experimental and analysis procedure as well as results and proposed future improvements will be discussed.

[1]          A. J. Spieles, K. Ji, J. N. Khalaf, H. Laubscher, H. Gahkani, and B. H. Evan, "Flowability and Attrition Characterization in Generation 3 Particle CSP Media," in Solar Paces, Rome, Italy, 2024. [Online]. Available: https://cdn.fourwaves.com/static/media/formdata/96da93e3-ad01-4b0b-9c17-7308bfaf5b58/00446622-5e95-4868-acba-c84c4e4dfc3f.pdf.

[2]          K. J. Albrecht and C. K. Ho, "High-temperature flow testing and heat transfer for a moving packed-bed particle/sCO2 heat exchanger," AIP Conference Proceedings, vol. 2033, no. 1, 2018, doi: 10.1063/1.5067039.

Presenting Author: Aaron Spieles Sandia National Laboratories

Presenting Author Biography: Aaron attended the University of Dayton as an undergraduate and to complete his Master of Science in Mechanical Engineering. While attending graduate school Aaron designed, built, and tested a lab scale heated falling particle experiment for use with a solar simulator to experimentally validate and improve Discrete Element Method (DEM) models of particle flow. After graduate school Aaron transitioned to the concentrated solar technologies group at Sandia National Laboratories and has been supporting many of the ongoing missions of the group since then. These include experimental and modeling efforts supporting CSP particle technology development and implementation, heliostats, barriers to heliostat field deployment, and many others. His current presentation is focused on evaluating granular media flow in critical material handling components at relevant CSP temperatures.