Session: 07-02: Fluidized Bed Heat Exchangers

Paper Number: 169874

169874 - Significant Heat Transfer Enhancement With Extended Surfaces in Narrow-Channel Fluidized Beds for Particle-Based Csp Applications 

Abstract: 

Concentrating solar power (CSP) with high-temperature thermal energy storage (TES) in oxide particles is a promising approach for dispatchable solar electricity using high-efficiency thermal power cycles operating above 700 °C.  Realizing the full potential of particle-based TES requires both a scalable particle receiver design and a high-performance particle-to-fluid, primary heat exchanger.  Indirect particle receivers, which heat the particles through confining walls, must sustain high heat fluxes to reduce receiver costs and heat loss without exceeding the temperature limits of the wall materials, while particle-based heat exchangers face high costs due to low overall heat transfer coefficients.   Particle-wall heat transfer coefficients exceeding 1100 W m^-2 K^-1 in smooth-wall fluidized bed channels [1,2] have encouraged the adoption of fluidized beds for both particle receivers and particle-to-fluid heat exchangers in CSP applications. However, even with these improvements, particle-wall thermal resistance remains the dominant limitation in both receivers and primary heat exchangers. In this study, we explore the use of extended surfaces in narrow-channel (bed depths Δ𝑧_b = 12.0 mm and width Δ𝑥_b = 100 mm) fluidized particle flows to enhance particle-wall h_T,w while mitigating particle dispersion effects. By increasing the heat transfer surface area without compromising counterflow fluidization, extended surfaces offer a pathway to achieving higher particle-wall h_T,w and improving the overall efficiency of CSP systems. 

Heat transfer tests using finned heat transfer walls with an aligned fin strip fin arrangement (assembled by Brayton Energy) explores the impact of heating and cooling modes, mean bed temperatures and solid mass fluxes on effective particle-wall heat transfer coefficient h_T,w,eff. Unlike smooth-wall fluidized beds, where h_T,wshows no significant dependence on heat flux direction, measured h_T,w,eff for finned wall beds shows much higher values for receiver mode (wall heating) than heat exchanger mode (wall cooling). At a mean bed temperature of 450 °C in receiver mode, the finned plates achieved h_T,w,eff values approaching 2500 W m^-2 K^-1 while in heat exchanger mode at around 250 °C , h_T,w,eff  reached 1500 W m^-2 K^-1 for the smaller CARBOBEAD HTM 200 (d_p = 210 mm) under mild fluidization. The results demonstrated that aligned fins, which increase the wall area by 350%, enhanced h_T,w,eff by factors of 2 to 3 compared to smooth-wall beds. Additionally, no significant dependence of h_T,w,eff on solid mass flux  was observed, consistent with previous findings for smooth-wall fluidized bed [3]. For heat exchanger applications, fluidized beds introduce particle dispersion driven by rising gas bubbles which reduces the log mean temperature difference and thus overall heat transfer [3].  Experiments across a wide range of operating temperatures and particle mass fluxes confirmed that the finned walls effectively suppress vertical dispersion especially for larger CARBOBEAD HSP 40/70 (d_p = 408 mm), improving the log-mean temperature difference in fluidized bed heat exchangers.  These findings establish a foundation for leveraging extended surfaces to achieve higher particle-wall heat fluxes, reduce particle heat exchanger costs, and enhance solar receiver performance in particle-based TES systems.

References

[1] J.R. Fosheim, X. Hernandez, W.J. Arthur-Arhin, A.B. Thompson and C.P. Bowen, K.J. Albrecht, and G.S. Jackson. “Narrow-channel fluidized beds for particle-sCO₂ heat exchangers in next generation CSP plants.” AIP Conference Proceedings, 2445, 160007 (2022).

[2] K.J. Brewster, J.R. Fosheim, W.J. Arthur-Arhin, K.E. Schubert, M. Chen-Glasser, J.E. Billman, G.S. Jackson. “Particle-wall heat transfer in narrow-channel bubbling fluidized beds for thermal energy storage,” International Journal of Heat and Mass Transfer, Volume 224, 2024,125276.

[3] W.J. Arthur-Arhin, J.R. Fosheim, K.J. Brewster, D.A. Madden, K.J. Albrecht, G.S. Jackson. “Demonstration of a multi-channel fluidized bed particle–supercritical carbon dioxide heat exchanger for concentrating solar applications.” Applied Thermal Engineering, Volume 248, Part B, 2024,123242.

Presenting Author: Fuqiong Lei Colorado School of Mines

Presenting Author Biography: Dr. Fuqiong Lei is a postdoctoral researcher at the Colorado School of Mines where she is working with Dr. Greg Jackson's research team on high-temperature particle-based energy storage, solar reactors, and high-temperature electrochemical systems. Lei has a Ph.D. in Chemical Engineering from Oregon State University where she studies solar reactors for reforming and thermochemical energy storage. She earned a B.S. and M.S. in Chemical Engineering from Hunan University.