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

Paper Number: 134640

134640 - Experimental Investigation of Granular Flows Under Concentrated Irradiation 

Abstract: 

Particulate-based solar thermal energy storage (TES) and transport media provide a pathway for sensibly storing solar energy to produce on-demand electricity in concentrated solar power applications. TES facilitates overcoming solar transients and enables nighttime operation. Particles have a distinct advantage over widely used molten salts, as they are capable ofoperating at elevated temperatures up to 1300 K and do not freeze at lower temperatures. Granular flows of sintered bauxite particles were examined along an inclined plane, directly exposed to concentrated irradiation from a high-flux solar simulator (HFSS). The goal of this work was to study the effects of large temperatures gradients in the flows and further inform the design of solar particle heating receivers/reactors.

An experiment apparatus to examine granular flow behaviors under concentrated irradiation was fabricated. The particles were placed in a storage hopper prior to experimentation at ambient temperature. Experimentation commenced when a particle valve located on the bottom of the hopper was remotely opened and the particles flowed along the incline plane with angle of 27° fabricated from high strength aluminosilicate boards. Concentrated irradiation from HFSS was introduced directly onto the granular flows with an exposed area of 200 × 80 mm². A high-speed camera and infrared radiation (IR) cameras (FLIR A655sc and FLIR A6261IR) were mounted normal to the inclined plane to capture the surface particle velocities and temperature gradients of the granular flows. An extensive calibration campaign of cameras was undertaken to filter out the reflected irradiation from the surface of the granular flow. Maximum surface temperatures of granular flows above 1100 K were observed at the central region of plane when exposed to average radiative heat fluxes of 600 kW/m². Overall, the particle surface velocities and mass flow rates decreased at elevated temperatures mainly due to increase inter-particle friction with temperature. The non-uniform irradiation induced a temperature gradient on the granular flow where the surface temperature decreased closer to the side of the plane. This resulted in unique flow behavior characteristics in which particles were guided to lower temperature spots where inter-particle friction was lower.

Transient two-dimensional numerical heat and mass transfer models were developed to predict temperatures of particles at both the surface and interior of granular flows. Experimentally measured particle surface velocities, mass flow rates of bed height and irradiation[LP1]   were adopted in the model. Particle velocity along the depth of the granular flow was modeled based on experimentally reported velocity profile observed in granular flows on inclined plane. Heat transfer within the granular flow was described by heat conduction with effective thermal conductivity calculated by Zehner, Bauer and Schlünder (ZBS) model. The  ZBS model requires particle volume fractions of the granular flow, which were obtained from the measured mass flow rates and modeled particle velocity profiles. The surface temperatures obtained from experiments and models showed good agreement. Particle velocity difference with change in depth were strongly correlated to changes in surface temperature, which increased rate with time. This study provides valuable insight into flow behaviors and relevant heat transfer of granular flows exposed to concentrated irradiation, which directly impact the efficiencies of particle-based solar receiver/reactors.

Presenting Author: Shin Young Jeong National Renewable Energy Laboratory

Presenting Author Biography: Dr. Jeong graduated PhD from Georgia Institute of Technology in Summer 2023. He was supervised by Dr. Zhuomin Zhang and Dr. Peter Loutzenhiser. He is currently a postdoctoral researcher at National Renewable Energy Laboratory working with Dr. Zhiwen Ma in various research projects related to concentrating solar power technologies.

Authors:

Shin Young Jeong National Renewable Energy Laboratory
Devesh Ranjan Georgia Institute of Technology
Zhuomin Zhang Georgia Institute of Technology
Peter Loutzenhiser Georgia Institute of Technology