Nano Particles In The Fluid Motion Feature Laser Self-mixing Measuring Methods

The coexistence of Brownian motion and translational motion in nanoparticledispersions has an important impact in some areas such as the heat transfer of thenanofluid, the size measurement of nanoparticle and so on. Thus, it is necessary toresearch the characteristics of these two motions using the appropriate measurementmethod. Up to now, the lack of relevant measurement method remains. This makes iturgent to develop the suitable measurement methods. The self-mixing technique ishopeful to be used as an online measurement method because of its single structure,self-alignment, avoidance of multiple scattering, avoidance of the disturbances fromscattering by large particle and from stray light, and so on. Thus, in the thesis, asystemic research on the self-mixing technique in the flowing Brownian motion systemis made on the basis of previous works.In theory, with the aid of the dynamic light scattering theory and Lang-Kobayashirate equation, a novel theory is developed for the laser-diode self-mixing technique inthe flowing Brownian motion system. Both the time autocorrelation function of theself-mixing signal and the power spectral density of the self-mixing signal are obtainedanalytically. The power spectral density is composed of two Voigt function. Numericalcalculation of the Voigt function is very important and is difficult in the engineeringfield. In order to evaluate the Voigt function fast and accurately, the series summationmethod (SSM) proposed by Limandri et al. is improved. The numerical computationsare made in different cases including nanosolution (i.e. pure Brownian motion), fluidwith large particles (i.e. pure translation motion) and nanofluid (i.e. Brownian motionand translation motion). The numerical results are analyzed, which establish thefoundation of experiment.The experimental setup is designed including the sample cell, the driver for laserdiode, and the AC-coupled transimpedance amplifier. The sample cell is such designedthat the type of flow occurring in a fluid is the laminar flow. The driver makes the laserdiode work in the constant operating current. The amplifier is designed for amplifyingthe small self-mixing signal and filtering the large DC signal. Both the timeautocorrelation and the power spectral density are measured in different cases. Theexperimental results agree with the numerical results. The obvious asymmetry of the Doppler peak is reasonably explained by using the theoretical analysis and numericalcomputation.The online equipment of self-mixing technique is researched. It is proventheoretically to be feasible that the power spectrum of self-mixing signal is obtainedusing an analog processing system which includes a series of channels. Each channelincludes a band-pass filter and a true root mean square (RMS) chip. The circuit based onmicrocontroller unit (MCU) is designed for the asynchronous serial communication ofsignals. The experimental results are in agreement with the numerical results.Finally the inversion method is studied so as to extract the parameters of particles.The well-known Kaczmarz inversion algorithm is improved. The particle size in thenanosolution is successfully extracted. When the flow velocity is low, the particle sizein the nanofluid can be extracted although the information of flow velocity is unknown.In the fluid with big particles, the ratio of flow velocity to beam waist radius can bederived although the information of particle size is unknown..