Session: 07-04: Modeling of Thermal Energy Storage and Receiver Systems

Paper Number: 170041

170041 - Two-Fluid Modeling of Narrow-Channel Fluidized Bed Heat Transfer for Particle Heat Exchangers and Receiver 

Abstract: 

Emerging Gen3 concentrating solar power (CSP) uses oxide particles as both the heat transfer medium for the capture of solar energy and the thermal energy storage (TES) material for enabling hot storage temperatures of 800 ^◦C or higher. Optimizing particle-based CSP systems with TES requires accurate modeling of components like particle receivers for capturing solar energy and primary particle heat exchangers for extracting thermal energy to power cycles.  Narrow-channel fluidized beds, which offer high bed-wall heat transfer coefficients, have been explored for Gen3 CSP heat exchangers [1] and for indirect particle receivers [2]. To assess the viability of fluidized beds for Gen3 CSP applications, reliable models are needed to assess component design and performance at the length scale and high-temperature and flow conditions characteristic of actual applications. For fluidized bed simulations, Eulerian-Eulerian two-fluid multi-phase flow models provide the ability to simulate fluidized bed dynamics at length and time scales that are necessary for performing component level analysis. However, semi-empirical terms for transport within these two-fluid models have not been calibrated for narrow-channel fluidized beds that have
been proposed for CSP-TES applications.

This study adopts two fluid models within ANSYS Fluent to explore the heat transfer behavior of narrow-channel beds with net-downward flowing fluidized particles (CARBOBEAD HSP 40/70) and upward flowing gas. The present work delves into how variations in bed width and particle inlet mass fluxes affect the fluidization dynamics and the bed-wall heat transfer, which is critical for optimizing CSP systems. Initial studies have revealed that the two-fluid model can be adjusted to fit how measured heat transfer coefficients vary with excess fluidization velocities for CARBOBEAD HSP 40/70 (mean d_p = 408 μm) . The fits were enabled by adjusting critical particle-wall interaction sub-models, but it has not been tested over a broad range of particle flow conditions. The study expands those initial studies by exploring how continuous downward particle flows in the 10-mm wide narrow-channel bed, with particle inlet mass fluxes up to 50 kg m⁻² s⁻¹ designed to replicate lab-scale experimental tests reported in previous studies [2].  A parametric study on fluidized bed channel width explores how bubble growth and associated thermal energy dispersion as well as bed-wall heat transfer vary with the channel width. Narrower bed widths for a fixed mass flow results in higher mass fluxes that tend to reduce heat transfer coefficients, but narrower beds impact particle dispersion that lowers particle heat exchanger log mean temperature differences, which drive heat transfer rates [3]. The reduction in
predicted wall heat transfer coefficients with increased particle mass fluxes has not been clearly observed in experimental studies [2], and efforts are ongoing to assess what aspects of the two-fluid transport models impact these predictions. The continued development of these models is critical to develop confidence in two-fluid models for use in fluidized bed heat exchanger and receiver design at scales relevant for CSP applications.

References
[1] K.J. Brewster, J.R. Fosheim, W.J. Arthur-Arhin, K.E. Schubert, M. Chen-Glasser, J.E. Billman, G.S. Jackson.  International Journal of Heat and Mass Transfer, 224:125276, 2024.

[2] K.J. Brewster, J. Martinek, F. Municchi, W.J. Arthur-Arhin, J.R. Fosheim, Z. Ma, G.S. Jackson. Solar Energy, 289:113322, 2025.

[3] W.J. Arthur-Arhin, J.R. Fosheim, K.J. Brewster, D.A. Madden, K.J. Albrecht, G.S. Jackson. Applied Thermal Engineering, 248:123242, 2024.

Presenting Author: Yahya Bokhary Colorado School of Mines

Presenting Author Biography: Yahya Bokhary is a Ph.D. candidate in the Department of Mechanical Engineering at the Colorado School of Mines. His research is on two-fluid modeling of fluidized bed heat transfer for CSP and high-temperature TES applications. Yahya has an M.S. in Mechanical Engineering from the School of Mines and B.S. in Mechanical Engineering from King Fahd University of Petroleum and Minerals.