Micrometer-sized graphite particles are widely found in nature and industry. Particularly, the graphite dust is an important problem for the pebble-bed high temperature gas-cooled reactor (HTGR), regarding the coupling with the fission products (FPs). Due to the highly irregular disk-like shape, a great gap still exists for understanding the transport-related behaviors of real graphite particles, including the settling velocity and drag coefficient. To address this issue, we present an experimental investigation on the free settling of micrometer-sized natural, IG-110, NG-CT-10 and A3-3 graphite particles. The steady settling process is filmed using a high-speed camera together with a microscope. Both the terminal settling velocity and the drag coefficient are measured. In the Stokes region, although the shape is highly irregular and diverse, the statistical results show that the drag coefficient still follows the form of Stokes law and scales inversely proportional to the particle Reynolds number. Adopting the Stokes form and modifying the coefficient, a new correlation is proposed for the drag coefficient. The fitted value is 30.7 ± 10.2 for natural graphite, 26.2 ± 7.5 for IG-110, 28.1 ± 8.4 for NG-CT-10 and 32.7 ± 8.3 for A3-3 particles, which are larger than 24 of the classical spherical Stokes solution. In a wide range of particle Reynolds number from 10⁻⁴ to 3, the Bagheri and Bonadonna's correlation well represents the drag coefficient of graphite particles. The results of this work can be easily incorporated into Eulerian-Lagrangian simulations and aerosol models in system analysis codes, and helps to improve the understanding and modelling of irregular disk-like graphite particles.

微米级的石墨颗粒在自然界和工业界广泛发现。特别地，关于与裂变产物（FPs）的耦合，石墨粉尘对于卵石床高温气冷反应器（HTGR）而言是重要的问题。由于高度不规则的盘状形状，在理解真实石墨颗粒的运输相关行为（包括沉降速度和阻力系数）方面仍然存在很大的差距。为了解决这个问题，我们提出了对微米级天然IG-110，NG-CT-10和A3-3石墨颗粒的自由沉降的实验研究。使用高速相机和显微镜拍摄稳定的沉降过程。测量终端沉降速度和阻力系数。在斯托克斯地区，尽管形状高度不规则且多种多样，统计结果表明，阻力系数仍然遵循斯托克斯定律的形式，并且与粒子雷诺数成反比。采用斯托克斯形式并修改系数，提出了一种新的阻力系数相关性。天然石墨的拟合值为30.7±10.2，IG-110的拟合值为26.2±7.5，NG-CT-10的拟合值为28.1±8.4，A3-3颗粒的拟合值为32.7±8.3，大于经典球形斯托克斯溶液的24。雷诺数范围广泛，从10起 IG-110为5，NG-CT-10为28.1±8.4，A3-3颗粒为32.7±8.3，大于经典球形Stokes解决方案的24。雷诺数范围广泛，从10起 IG-110为5，NG-CT-10为28.1±8.4，A3-3颗粒为32.7±8.3，大于经典球形Stokes解决方案的24。雷诺数范围广泛，从10起^-4至3，Bagheri和Bonadonna的相关性很好地表示了石墨颗粒的阻力系数。这项工作的结果可以轻松地纳入系统分析代码的欧拉-拉格朗日模拟和气溶胶模型中，并有助于增进对不规则盘状石墨颗粒的理解和建模。