Session: 05-09 Particles for Thermal Storage in CSP 2

Paper Number: 116863

116863 - Enhanced Heat Transfer in Indirect Particle Receivers With Bubbling Fluidization 

Particle-based thermal energy storage (TES) has been identified by the DOE to meet cost targets for next-generation (Gen-3) concentrating solar power (CSP) plants[1]. One outstanding challenge for high-temperature particle TES for CSP involves the design of robust and efficient particle receivers. Designs include falling particle-curtains[2],[3], rotary kilns[4], and indirect particle cavity receivers[5]. Low particle-wall heat transfer coefficients h_T,w in indirect receivers limit the allowable incident wall solar fluxes to protect structural walls from thermomechanical failure.  Recent experimental studies by our team exploring particle-wall heat transfer in narrow-channel fluidized beds between 12 and 18 mm deep have shown that mild bubbling fluidization can increase local h_T,w in excess of 1000 W m^-2 K^-1 [6] for small particles below 250 um in diameter. These measurements are largely from batch mode experiments, where a fixed volume of fluidized particles are heated on one wall with external near-IR lamps and cooled on the opposite with external convective air cooling. This presentation extends that work with extensive continuous flow experiments simulating an indirect particle receiver flow path, where downward flowing particles are heated with external lamps on both walls as they fall through the narrow channel test section. Continuous flow enables study of dispersion due to reversal of some particles flowing against the net bulk flow with counterflowing gas bubbles rising through the bed. Dispersion flattens bed temperature profiles, which can reduce thermal stresses on indirect receiver walls and lower maximum wall temperatures. In this work we discern whether or not mass flux impacts local particle-wall heat transfer and investigate the influence of particle and gas flow rates, particle properties, and temperature on axial dispersion, which cannot be ascertained from batch mode experiments.

The continuous flow experiments were performed on multiple particle types including various CARBOBEAD particles (HSP 40/70 and CP 40/100) and sands (olivine LE120 and silica W7020). The dependence of h_T,w on particle diameter and local bed temperature follow the trends of the past measurements of our group and Molerus[7]. An empirical correlation[8] of the maximum Nusselt Number Nu_max based on the laminar Archimedes number Ar_lam and dimensionless excess fluidization velocity Û fits the measurements extremely well. Dependence of particle type is captured in the Ar_lam correlation and shows increased h_T,w with decreased particle size d_p. Tests to-date have studied particles up to 500 ^oC and observed local h_T,w above 1100 W m² K^-1 with olivine sand. Particle flow rates of 5-30 kg m^-2 s^-1 and excess gas flow rates up to Û = 80 have been explored.

[1] Mehos, et al. 2017. Concentrating solar power gen3 demonstration roadmap. NREL Technical Report .

[2] Ho, C., et al., 2017. Journal of Solar Energy Engineering 139.

[3] Kim, J.S., Kumar, A., Corsi, C., 2017. Design boundaries of large-scale falling particle receivers. AIP Conference

Proceedings 1850, 030029. URL: https://aip.scitation.org/doi/abs/10.1063/1.4984372 , doi:10.1063/1.4984372,

arXiv: https://aip.scitation.org/doi/pdf/10.1063/1.4984372.

[4] Miriam Ebert, et al, "Operational experience of a centrifugal particle receiver prototype", AIP Conference Proceedings 2126, 030018 (2019) https://doi.org/10.1063/1.5117530

[5] Martinek, J., Ma, Z., 2015. Granular Flow and Heat-Transfer Study in a Near-Blackbody Enclosed Particle

Receiver. Journal of Solar Energy Engineering 137. URL:https://doi.org/10.1115/1.4030970, doi:10.1115/1.4030970,arXiv:https://asmedigitalcollection.asme.org/solarenergyengineering/article-pdf/137/5/051008/6327573/sol_137_05_051008.pdf.051008.

[6] Jesse R. et al, "Narrow-channel fluidized beds for particle-sCO2 heat exchangers in next generation CPS plants", AIP Conference Proceedings 2445, 160007 (2022) https://doi.org/10.1063/5.0085934

[7] Molerus, O., 1992. Heat transfer in gas fluidized beds part 2. dependence of heat transfer on gas velocity. Powder Technology 70,15–20.

[8] Jesse R. Fosheim et al, G.S. Jackson. Design of a 40-kWth Counterflow Particle-Supercritical Carbon Dioxide Narrow-Channel Fluidized Bed Heat Exchanger. accepted for publicaion in AIP Proceedings 2022

Presenting Author: Keaton Brewster Colorado School of Mines

Presenting Author Biography: I am a 2nd year PhD student of Mechanical Engineering at the Colorado School of Mines. I am focused on narrow channel fluidized bed solid particle receivers for concentrating solar power. I primarily perform experiments here at mines simulating receiver-like conditions, but also do reduced order modeling of fluidized beds.