Particle convective heat transfer near the wall in a supercritical water fluidized bed by single particle model coupled with CFD-DEM--颗粒学报PARTICUOLOGY

Zhang, T., Wan, Z., & Lu, Y. (2023). Particle convective heat transfer near the wall in a supercritical water fluidized bed by single particle model coupled with CFD-DEM. Particuology, 73, 47-58. https://doi.org/10.1016/j.partic.2022.03.005

Particle convective heat transfer near the wall in a supercritical water fluidized bed by single particle model coupled with CFD-DEM

Tianning Zhang ^{a b}, Zhen Wan ^a, Youjun Lu ^a *

a State Key Laboratory of Multiphase Flow in Power Engineering (SKLMFPE), Xi'an Jiaotong University, Xi'an, 710049, Shaanxi, China
b Xi'an Electronic Engineering Research Institute, Xi'an, 710100, Shaanxi, China

10.1016/j.partic.2022.03.005

Volume 73, February 2023, Pages 47-58

Received 16 January 2022, Revised 14 March 2022, Accepted 28 March 2022, Available online 4 May 2022, Version of Record 17 May 2022.

E-mail: yjlu@mail.xjtu.edu.cn

Highlights

• Particle convective heat transfer (h_pc) in supercritical water fluidized bed is studied by single particle model.

• Particle residence time increases with thermal gradient layer thickness (λ).

• Particle residence time distribution near the wall follows a gamma function.

• h_pc first decreases and then increases with rising λ at higher velocity.

Abstract

Supercritical water fluidized bed (SCWFB) is a promising reactor to gasify biomass or coal. Its optimization design is closely related to wall-to-bed heat transfer, where particle convective heat transfer plays an important role. This paper evaluates the particle convective heat transfer coefficient (h_pc) at the wall in SCWFB using the single particle model. The critical parameters in the single particle model which is difficult to get experimentally are obtained by the computational fluid dynamics-discrete element method (CFD-DEM). The contact statistics related to particle-to-wall heat transfer, such as contact number and contact distance, are also presented. The results show that particle residence time (τ), as the key parameter to evaluate h_pc, is found to decrease with rising velocity, while increase with larger thermal boundary layer thickness. τ follows a gamma function initially adopted in the gas–solid fluidized bed, making it possible to evaluate hpc in SCWFB by a simplified single particle model. The theoretical predicted hpc tends to increase with rising thermal gradient thickness at a lower velocity (1.5 U_mf), while first decreases and then increases at higher velocity (1.75 and 2 U_mf). hpc occupies 30%–57% of the overall wall-to-bed heat transfer coefficient for a particle diameter of 0.25 mm. The results are helpful to predict the overall wall-to-bed heat transfer coefficient in SCWFB combined with a reasonable fluid convective heat transfer model from a theoretical perspective.

Graphical abstract

Keywords

Supercritical water; Fluidized bed; Particle residence time; Discrete element method; Single particle model

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