Understanding the influencing mechanism of turbulent fluctuation on the ignition characteristics of millimeter coal particles is essential. In this work, to study the effect of turbulent fluctuation on ignition time, millimeter coal particles are subjected to a specific flow field, generated in a furnace with symmetric fans. A one-dimensional model with the new proposed correlation and the Ranz-Marshall (R-M) correlation for (Nusselt number) is established to simulate the coal ignition process. In addition, the effects of fan speed, temperature, particle diameter, particle distance and coal type on the ignition time are investigated. It is found that an increase in fan speed from 0 to 3000 rpm leads to a particle Reynolds number increase from 0 to 22.5, and a turbulent particle Reynolds number ∗ increase from 0 to 71.5. With a consideration of the fluctuation effect, the new correlation of gives a better prediction of ignition time compared to the R-M correlation. Moreover, the ignition time is revealed to decrease with an increasing fan speed and an elevating temperature. While the ignition time shows merely an initial boost with enlarging particle distance, it exhibits a linearity with the term of particle diameter and Reynolds numbers () ( is turbulent Nusselt number). Based on this relationship, the difference of predicted ignition time is calculated at different and ∗. It is shown that at low or high ∗ values, the new correlation should substitute for the R-M correlation.

中文翻译：

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湍流脉动对毫米粒子点火的影响：基于努塞尔数新相关性的实验研究和数值模拟

了解湍流脉动对毫米煤颗粒着火特性的影响机制至关重要。在这项工作中，为了研究湍流脉动对点火时间的影响，毫米煤颗粒受到具有对称风扇的炉子中产生的特定流场的影响。建立了具有新提出的相关性和（努塞尔数）的 Ranz-Marshall (RM) 相关性的一维模型来模拟煤的着火过程。此外，还研究了风机转速、温度、颗粒直径、颗粒间距和煤种对点火时间的影响。研究发现，风扇转速从 0 rpm 增加到 3000 rpm 导致粒子雷诺数从 0 增加到 22.5，湍流粒子雷诺数 * 从 0 增加到 71.5。考虑到波动效应，与 RM 相关性相比，新的相关性可以更好地预测点火时间。此外，点火时间随着风扇速度的增加和温度的升高而缩短。虽然点火时间仅显示随着颗粒距离的增大而初始增加，但它与颗粒直径和雷诺数（）（是湍流努塞尔数）项呈现线性关系。根据该关系，计算不同 和 时预测点火时间的差值。结果表明，在低或高 * 值时，新的相关性应该取代 RM 相关性。