Rainbow Technique For Measurement Of Droplets Parameters

Atomization spray technology is widely used in industrial process and daily life.The spray process plays a leading role in many industrial applications,including spray burning,spray cooling,spray drying,and spray dust.Accurate measurement of spray parameters is useful for improvement of the efficiency and control of industrial processes.Therefore,it is of great importance to develop measurement techniques for spray droplet parameters.Rainbow technique is one of droplet parameter measurement methods based on light scattering.Compared with traditional scattering technology,it has the advantages of being real-time,non-intrusiveness,and high precision.In this thesis,the rainbow technique for droplet parameters are investigated numerically and experimentally.The basic principles of Geometrical Optics theory,Airy theory,Lorenz-Mie theory,Debye series decomposition theory and Nussenzveig theory are introduced.The accuracy and calculation efficiency of these theories are studied and compared under various droplet parameters.Mie theory is used to simulate rainbow signal of uniform droplet.The influences of droplet parameters on the scattering intensity distribution are systematically analyzed.An inversion algorithm of droplet parameters is proposed based on Mie theory.At the initial stage of droplet evaporation,the internal temperature distribution of the droplet is inhomogeneous.Debye series decomposition is used to simulate rainbow signal of inhomogeneous droplet.The evaporation equations of droplet produce an effect on scattering intensity distribution.The numerical results show that the temperature distribution curve in the cubic polynomial model concides with the experimental curve.There is no need to measure the droplet surface temperature with the supplementary temperature meter.Rainbow refractometry in combination with the cubic polynomial model is of high inversion accuracy and can correctly achieve the internal temperature distribution of evaporated droplet.On the basis of Nussenzveig theory,Quantum-behaved Particle Swarm Optimization(QPSO)is used to optimize the droplet refractive index and particle size distribution,and the algorithm is validated by the simulated full rainbow signal.The numerical results show that Nussenzveig theory is more efficient than Mie theory.The improved algorithm has high inversion accuracy and strong anti-noise ability.It can accurately achieve the size distribution of droplet.To validate the feasibility of the proposed inversion algorithms,the experiments are carried out.A monochrome laser is used to illuminate liquid column and spray droplets,the rainbow scattered by the measured objects are captured by a CCD.The inversion algorithm is used to measure the particle size and refractive index of the above objects.The experimental results show that,rainbow refractometry in combination with QPSO is of high inversion accuracy,the refractive index calculation error is less than o× 10-4.The error of particle size calculation is less than 9%.