Investigation On Bubbles And Pulverized Coal Particles Measurement With Interferometric Particle Imaging

Multiphase flows widely exist in natural environment and industrial production.The quantification of particle parameters in multiphase flow is of great significance in understanding the mechanism of multiphase flow and optimizing equipment and production process.After years of development of interferometric particle imaging(IPI),the type identification and parameter measurement of spherical transparent particles and irregular particles in the fluid field have been realized,which has scientific significance and practical value for the study of multiphase flow.With interferometric particle imaging,the size and transient size change of spherical transparent bubbles,and the size and morphology of irregular opaque pulverized coal particles are measured and studied.The main research contents of the paper are as follows.For the measurement of spherical transparent particles with refractive index smaller than 1,a technique called phase critical angle scattering(PCAS)is proposed to measure the transient nanoscale size change of micron-sized particles.The theoretical derivation shows that the phase of the high-frequency fine structures in the critical scattering signals is highly sensitive to,and shifts linearly with,the change of particle size.Based on the Debye series expansion model,the critical scattering signals of bubbles with different refractive indexes and sizes are calculated and analyzed,and the feasibility of the PCAS technique is verified by simulation.A single-bubble generator was designed,and the size and size change of the single rising bubble were measured with PCAS.Simulation and experimental results show that the phase critical angle scattering technique can measure the size growth of micron-sized bubbles down to tens of nanometers,providing a powerful tool for the study of bubble dynamics.For irregular particle measurement,a dual-beam interferometric particle imaging(DIPI)system is proposed for opaque particles.The system illuminates the side of the particle facing to the camera with dual-view beam illumination,and the obtained interferogram contains more accurate size and morphology information than the traditional one beam illumination.In order to investigate the accuracy of dual-beam interferometric particle imaging,a digital inline holography(DIH)system was introduced in the experimental system.The red and green channels of the color camera were used to record the DIH signal and the DIPI signal respectively,and the same projection of the same pulverized coal particle was measured simultaneously with DIH and DIPI.The results show that the two-dimensional Fourier transform of the DIPI interferogram and the two-dimensional autocorrelation of the corresponding DIH reconstructed in-focus image have good consistency in shape,and the relative deviation of the size is within 9%.Thus,the accuracy of the dual-beam interferometric particle imaging system for the measurement of micron-sized opaque particles was verified by experiments.In addition,the backward arrangement of the interferometric particle imaging system facilitates the subsequent instrumental development and practical application.This work develops the phase critical angle scattering technique for the measurement of bubble size and transient size change,and proposes a dual-beam interferometric particle imaging system for the measurement of irregular opaque particles.It provides new ideas for the expanded application and instrumental development of interferometric particle imaging,and provides new tools for particle measurement in multiphase flow.