Digital Particle Holography For3D Measurement And Its Applications

Multiphase flows are widely applied to various industrial productions, such as energy engineering. The comprehensive understanding of the machanism of multiphase flow relies on the quantantitive3D measurement of the particles. Holography is a real3D imaging technique, and has shown great protential in3D measurement. Applications of digital holography for the3D measurement of particle flow are of significant scientifical importance and practical value. By employing theoretical analysis, numerical simulation and experiments, the simultaneous measurements of the3D position, morphology,3D velocity and even rotation of a transient particle flow were systematically investigated.On the particle holography theory, particle hologram with multi-particle, at arbibrary angle and under an elliptical Gaussian beam illumination was modeled in the framework of generalized Lorenz-Mie theory, and results show that the particle hologram can have four typical fringes:concentric ellipses, concentric rings, hyperbolic curves and parallel lines. The formation of two systems of rings for the transparent particle in the near field was revealed by Debye series. A model for the particle inline holography system with imaging lens system was built in the framework of light diffraction, and the features of holograms with infocus or defocus partile, or even with astigmatism, can be obtained. This model can characterize the particle holography in a container with curved suface. A joint model combining the light scattering and diffraction was proposed to characterize particle hologram at arbitrary direction and with lens system.On the particle hologram processing, by introducing the reconstruction coeffecient to the class symetric reconstruct kenerls for phase compensation, the modified convolution method, asymetric wavelet method were proposed to reconstruct the particle hologram with elliptical Gaussian beam illunimation. Comparision between various locating method shows that the local variance of intensity gradient in wavelet domain can accurately locate bubbles, droplets and opaque particles. The focus metric curve of a particle in the two frames in DHPTV presents spatial correlation, and the depth displacement can be directly evaluated from the crosscorrelation of the two focus metric curves, which has the advantage of avoid of the depth displacement error propagated from the depth location error. The relationship of particle size, velocity and ratation speed was formulated for accurate rotation measurement of nonspherical particle with DHPTV, which could be retrieved by feature matching of the reconstructed infocus image.A digital particle holography system for3D particle measurement was established. Calibration results show that the system can accurately measure the particle morphology. The absolute error in particle locating is less than500μm from80.0mm to240.0mm, with the relative error less than2.5%. The average of depth displacement error is about50μm, with the relative error less than10%. By heterogeneous parallel programming with CPU+GPU, the hologram processing can speed up to15times.The digital particle holography system was applied to various real particle flows, including the burning coal particles in a pulverized coal jet flame, bubbles in an electrolysis cell, glass particles in a pipe, microchannel flow and boudary flow near the wall, and the particle size and shape,3D position and velocity of the intorregated flows were obtained.This work positively contributes to the development of digital holography for the3D measurement of particle flow, and offers experimental tools for the intensive investigation of particle dynamics.