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建立带有玻璃窗的由“煮黑”工艺完成的矩形通道实验装置,对已有的颗粒动态分析(particle dynamicsanalyzer,PDA)测量技术进行了改进,并以此方法对矩形通道内的不均匀温度场中近壁区的亚微米颗粒的运动情况进行了测量。改进的PDA测量方式可更有效地了解近壁面颗粒运动状况。利用实验数据对在温度场中亚微米颗粒的受力情况和运动情况进行了分析。研究表明:亚微米颗粒在湍流温度场中运动,既有湍流和热泳的沉积效应,也存在较小颗粒的团聚效应。热泳力对较小粒子的作用强于较大粒子,但如果粒径太小,粒子在主流中的跟随性变强。热泳力对亚微米颗粒作用较强,湍流对较大颗粒作用较强。由于亚微米颗粒能够跟随气流运动,对沉积也带来不利的影响。当温度较高时,在边界层内,热泳力超过由于速度梯度造成的横向沙夫曼力,是使细颗粒发生热泳沉积的重要原因。布朗扩散可能对亚微米颗粒运动起到主导作用。
A rectangular channel experiment device with glass window, which is completed by “Boiling Black” process, is established to improve the existing measurement technology of particle dynamics analyzer (PDA). In this way, The submicron particle motion near the wall in a uniform temperature field was measured. Improved PDA measurements allow for a more efficient understanding of near-surface particle motion. The experimental data were used to analyze the force and movement of submicron particles in the temperature field. The results show that submicron particles move in the turbulent temperature field, and have the effect of sedimentation of turbulent flow and thermophoresis as well as agglomeration of smaller particles. The effect of thermophoretic force on smaller particles is stronger than that of larger particles, but if the particle size is too small, the particle’s followability in the mainstream becomes stronger. The effect of thermophoretic force on sub-micron particles is stronger and turbulence is stronger on larger particles. As sub-micron particles can follow the air movement, the deposition also adversely affected. At higher temperatures, the thermophoretic forces in the boundary layer exceed the transverse Schaffer forces due to the velocity gradient, which is an important reason for the thermophoretic deposition of fine particles. Brownian diffusion may play a dominant role in submicron particle motion.