高速圆射流中典型非球形颗粒的扩散特性  

Dispersion characteristics of typical non-spherical particles in a high-speed round jet

作　　者：黄文仕 吴玉新[1] 冯乐乐 张缦[1] 张扬[1] HUANG Wenshi;WU Yuxin;FENG Lele;ZHANG Man;ZHANG Yang(Key Laboratory for Thermal Science and Power Engineering of Ministry of Education,Department of Energy and Power Engineering,Tsinghua University,Beijing 100084,China)

机构地区：[1]清华大学能源与动力工程系,热科学与动力工程教育部重点实验室,北京100084

出　　处：《清华大学学报（自然科学版）》2020年第6期485-492,共8页Journal of Tsinghua University(Science and Technology)

基　　金：国家自然科学基金资助项目(51761125011);国家质检总局科技项目(2017QK178-02)。

摘　　要：低氧稀释(moderate and intense low-oxygen dilution,MILD)燃烧具有传热均匀、NO_x污染物排放低的特点。新一代MILD煤粉燃烧技术主要通过高速射流引起强烈的湍流混合来实现。其中,煤颗粒在高速射流中的扩散行为非常关键。目前对球形颗粒在气固射流中扩散行为的研究已非常深入,然而化石燃料属于典型的非球形颗粒,其在射流中的扩散行为与球形颗粒具有一定的差异,该类非球形颗粒在高速射流下的扩散特性值得进一步研究。为此,该文采用玻璃珠、玻璃渣和煤粉等颗粒开展了宽Re范围下的高速两相圆射流实验,通过激光Doppler相位分析技术(phase-Doppler anemometry,PDA)获取并分析了颗粒的质量浓度、速度及湍动能分布随球形度、粒径以及射流速度的变化规律。结果表明:非球形颗粒在射流中的质量浓度、速度、湍动能分布与粒径较小的球形颗粒具有一定相似性,但其扩散行为不能仅通过Stokes数进行定量表征,除曳力之外,升力对非球形颗粒扩散也具有一定影响;与球形颗粒相比,非球形颗粒的扩散更为显著,其主要原因是其径向湍动能显著增强所致;射流速度的增加促进了颗粒的剪切层集聚和径向扩散,对非球形颗粒的促进作用更强。Moderate and intense low-oxygen dilution(MILD)combustion is appealing due to its uniform heat flux profile and low NOx emissions.The new generation of MILD coal combustion burners use high-speed jets with strong turbulent mixing.The dispersion of the coal particles in the high-speed jet is a key issue in such systems.There are many studies of the dispersion of spherical particles in particle-laden jets in the literature.However,the dispersion of fossil fuel particles,which are typically not spherical,differs from that of spherical particles,so the dispersion characteristics of these non-spherical particles in high-speed jets still deserves further study.This study used glass beads,glass powder and pulverized coal as the solid phase in a high-speed two-phase round jet for a wide range of Reynolds numbers.The particle concentrations,velocities and turbulent kinetic energy distributions were measured for various particle sphericities,sizes and jet velocities using laser phase-Doppler anemometry(PDA).The results show that the concentration,velocity and turbulent kinetic energy distribution characteristics of non-spherical particles are similar to those of smaller spherical particles.However,the non-spherical particle dispersion cannot be accurately characterized by just the Stokes number since the lift can strongly affect the particle dispersion.Non-spherical particles are more easily dispersed than spherical particles,mainly due to a significant increase in the radial turbulent kinetic energy.Increasing the jet velocity promotes the shear layer growth and radial dispersion of the particles and more strongly influences the non-spherical particle dispersion than the particle size or sphericity.

关 键 词：气固两相流 高速射流 颗粒扩散 球形度 

分 类 号：O359[理学—流体力学]