纳米流体的激光自混频功率谱密度研究

Research on Power Spectral Density of Self-Mixing Signal in Nanofluid

纳米流体运动特性和颗粒参数的测量对纳米流体换热效率的研究具有重要意义。本文将激光自混频技术应用于纳米流体测量中,给出了自混频信号功率谱密度函数的表达式并实验研究其变化规律。研究结果表明,功率谱密度展宽具有佛克脱函数的形式。激光垂直入射流动样品池时,功率谱密度得到展宽,展宽程度随着定向流速的增大或束腰半径的减小而增大。激光倾斜入射流动样品池时,功率谱密度在展宽的同时还伴随多普勒峰移,其位置随着定向流速的增大或散射矢量与定向流速之夹角的减小而迁移至高频。

Measurement of motion characteristics and parameters of nanofluid is of very importance on the research of heat transfer of nanofluid.In this paper,the laser self-mixing technique is employed to research the characteristics of nanofluid.The power spectral density（PSD）of self-mixing signal is derived theoretically and studied experimentally.It is showed that the power spectral density is in the profile of Voigt function.While the laser beam propagates along the direction perpendicular to the flow velocity,the PSD becomes wider due to the increase of the flow velocity and/or the decrease of the beam waist.If the laser beam is oblique to the flow velocity,besides the broadening of the spectrum,the PSD displays a Doppler peak whose position shifts to higher frequency as the translational flow velocity increases and/or the angle between scattering vector and flow velocity decreases.