The Research On The Measurement Of Micrometer-Size Droplet Diameter Using Electrodynamic Balance

In the process of microchemical engineering, the research on the transfer phenomena on the surface concerning micrometer-size particle and droplet is of important basic significance. The kinematic and mass transfer experimental data obtained by microparticle localized observation and measurement in the condition of process indicate that the combined use of electrodynamic balance and light scattering technique can realize the on-line follow of microparticle mass transfer kinetic phenomena in the gas-droplet two-phase flow. In the mass transfer experiment of this thesis, using the improved octopole double-ring electrodynamic balance to suspend the dodecanol microdroplet, the author uses a He-Ne laser source to produce perpendicularly polarized laser beam. And according to the light scattering data recorded by a 512 element linear photodiode array, the author measures the change of droplet diameter by the curve fitting of phase function and calculates the change of droplet weight based on it, with the final result correct to 1 ×10~7mg.Based on Lorenz-Mie theory, the author realizes the fast and correct measurement of droplet diameter by comparing the theoretical curve with the experimental one of phase function. During data processing, theauthor uses computer advanced programming language LabVIEW to conduct the curve fitting of phase function, improving its extent of automatization.The author uses Lorenz-Mie theory to analyze the sensitivity of the peak characteristics of phase function to the change of droplet diameter. The larger droplet diameter is, the more phase function reflects the characteristics of nn and in functions of high order, i.e., the denser its peaks are. The curve fitting of phase function lies on the peak characteristics of the two curves, including the number, position, shape and relative amplitude of peaks. It is proved by this thesis that there is a linear relation between the peak number of phase function and droplet diameter in certain condition.Using frequency spectrum analysis of phase function to calculate its auto power spectrum can reflect its frequency structure. The auto power spectrum of phase function commonly has two extreme frequencies, and the corresponding frequency components decide the peak characteristics of phase function. There is also a linear relation between the main oscillation extreme frequency and droplet diameter.During the elementary curve fitting of phase function, the author produces standard curve with the help of theoretical curve of phase function, reflecting the linear relation between the peak number of phase function and droplet diameter. When using direct method of finding extremum and indirect method of frequency spectrum analysis to calculate the peak number of phase function, the relative errors of droplet diameter estimation are respectively <20% and <2%. So, frequency spectrum analysis of phase function helps to improve the precision of droplet diameter estimation.During the concrete curve fitting of phase function, based on the theory of least-squares analysis, the author replaces equidistantly selecting data by purposefully doing it, enabling the choice of data toreflect more influence of the peak characteristics of phase function on its curve fitting. The final determination of droplet diameter can be correct to 0.01μm, and the peak characteristics of the two curves fit very well.