燃料在强湍流中的燃烧广泛存在于实际工业装置中，研究湍流脉动对燃料传热及着火的作用对准确理解燃烧过程具有重要意义。目前，对于气体燃料和液滴在湍流脉动条件下的蒸发着火等过程已经有了非常详细的研究，而对于固体颗粒受热和着火的研究，大多数试验方法，如落管炉、单颗粒炉和平焰燃烧器等，是在层流条件下进行的。湍流条件下的研究方法主要包括高速射流、一维炉和旋流燃烧器，但普遍存在着光学可视性较差以及湍流强度难以调控等问题。为此，通过搭建能够在高温下运行的四风扇对冲实验装置，建立起湍流强度可调的近均匀各向同性湍流场，研究了湍流脉动对毫米级单颗粒升温及着火的作用。通过在不同风扇转速及环境温度下测量流场的瞬态速度分布以及颗粒温升曲线，获得了不同环境温度及湍流强度下颗粒的传热特性。基于粒径为4.4 mm的铜球传热试验结果提出了考虑湍流脉动作用的颗粒传热模型，并利用粒径为2.0 mm的铜球升温试验数据进行模型验证。研究结果表明，所建立试验台测量区域流场的脉动速度具有各向同性特征，且远大于时均速度，脉动速度大小随着风扇转速线性增加。脉动速度的增大使得煤颗粒着火提前、铜球颗粒升温速率加快，说明湍流对颗粒传热的强化作用不可忽略。通用的Ranz-Marshall公式会明显低估强湍条件下颗粒的升温历程，进而造成计算的颗粒着火延迟时间偏大。通过在Ranz-Marshall公式中引入附加的湍流作用项，并根据强湍流场中的试验结果拟合其中的系数，可以准确地表征湍流对大颗粒传热的强化作用。

The combustion of fuel in strong turbulent field widely exists in actual industrial devices. It is very important to study the effect of turbulence fluctuation on the heat transfer and ignition of fuel for accurately understanding combustion process. At present, there have been some very detailed studies on the evaporation and ignition of gaseous fuels and droplets in turbulent flow field, while for the study of heating and ignition of solid particles, most experimental methods, such as drop tube furnace, single particle furnace, and flat flame burner, etc., are laminar flow field. Research methods with turbulent flow filed mainly include high speed jet, one dimensional furnace and swirl burner, but there are some problems such as poor optical visibility and difficulty in controlling turbulent intensity. To this end, by establishing a four fan counter turbulence test rig that can operate at high tem peratures, a near homogeneous and isotropic turbulent flow field with adjustable turbulence intensity was estab lished, and the effect of turbulence intensity on the heating and ignition of single particles in millimeter scale was studied. By measuring the transient velocity distribution of the flow field and the heating curve of particle at different fan speeds and temperatures, the heat transfer characteristics of the particles at different temperatures and turbulence intensities were obtained. Based on the experiment results of the heating of a copper particle with a diameter of 4.4 mm, a particle heat transfer model considering turbulence fluctuation was proposed, and the model was validated using the experimental data of a copper particle with a diameter of 2 mm. The research results show that the flow field of the measurement area is isotropic and the fluctuation velocity is much larger than the time average velocity. The fluctuation velocity increases linearly with the fan speed. With the increase of fluctuation velocity, the ignition of coal particles is advanced and the heating rate of a copper particle is accelerated, indicating that the effect of turbulence on the enhancement of heat transfer cannot be ignored. The general Ranz Marshall correlation will obviously underestimate the heating history of the particles under strong turbulence conditions, thus causing the calculated particle ignition delay time to be too large. By introducing an additional turbulent effect term into the Ranz Marshall correlation and fitting its coefficients according to the experimental results in a strong turbulent flow field, the enhancement effect of turbulence on the heat transfer of large particles can be accurately characterized.

1 试验

   1.1 试验台与测量装置

2 试验结果与分析

   2.1 湍流流场特性分析

   2.2 湍流强度对铜球颗粒升温的影响

   2.3 湍流强化颗粒传热模型

   2.4 湍流强度对煤颗粒着火的影响

3 结论