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Volume 115
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Settling dynamics of micro-sized char and coal powders: An experimental study
Wenyu Tu a 1, Peilin Tian a 1, Liang-Liang Fan b *, Liang Zhao a *
a State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Xi'an, 710049, China
b School of Instrument Science and Technology, Xi'an Jiaotong University, Xi'an, 710049, China
10.1016/j.partic.2026.05.022
Volume 115, August 2026, Pages 356-365
Received 3 February 2026, Revised 17 May 2026, Accepted 29 May 2026, Available online 6 June 2026, Version of Record 19 June 2026.
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Highlights

• Drag coefficients for char particles are derived for the first time.

• Stokes and Schiller drag formulations are revised for coal and char particles.

• Rough char surfaces from pyrolysis yield higher drag coefficients.

• The model modified by this work refines char pneumatic conveying simulations.


Abstract

Char particles from coal pyrolysis exhibit unique settling dynamics, such as terminal velocity and drag coefficient. Accurate quantification of drag characteristics is essential for pneumatic conveying. Current simulations adopting spherical drag models suffer large deviations for irregular char particles. To fill this gap, we built a visual platform to investigate free settling of coal and char particles (<200 μm). Terminal velocities were measured for individual particles and aggregates. Based on statistical analysis, we revised Stokes and Schiller drag formulations. In the Stokes form, the fitted coefficients for individual coal particles and coal aggregates are 26.04 ± 3.5 and 52.15 ± 4.8, respectively; for individual char particles and char aggregates, they are 41.05 ± 3.2 and 112.4 ± 4.3, respectively. In the Schiller form, the fitted coefficients for individual coal particles and coal aggregates are 26.19 ± 3.4 and 53.88 ± 4.2, respectively; for individual char particles and char aggregates, they are 40.94 ± 3.2 and 111.1 ± 4.2, respectively. These correlations can be directly employed in drag model for numerical simulation of char pneumatic conveying. Validation shows significantly improved accuracy. This work presents the first experimentally derived drag coefficient correlations for char particles, addressing the lack of quantitative data and offering a more precise tool for char transport design.

Graphical abstract
Keywords
Settling dynamics; Char powder; Coal powder; Drag coefficient; Settling velocity
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