An improved Global Rainbow Refractometry for spray droplets characterization based on five-point method and optimization process

• An improved reversion algorithm of Global Rainbow Refractometry is proposed.
• Some parameters in algorithm are initially estimated according to the global rainbow.
• The inversion result of refractive index is of the order of magnitude 10−4.
• The error of the inversion result of mean diameter is less than 3 μm.
• The reconstructed rainbow agrees with the captured rainbow well.

Atomization and spray is now widely used in many industrial fields. On-line measurement of the size distribution, temperature, and component concentration of the spray droplets is very important for the in-depth investigation into the mechanism and optimized control of the atomization and spraying process. Global Rainbow Refractometry (GRR) is an effective light scattering technique for the simultaneous measurement of the size distribution and refractive index of the spray droplets. In the paper, an improved reversion algorithm of GRR is proposed based on Nussenzveig theory, least square method and empirical formulas. Firstly five characteristic points are extracted from the intensity distribution of the pretreated global rainbow, and then the refractive index and diameter range of the droplets can be initially estimated. From the initially estimated values, the refractive index and diameter range of the droplets are determined by optimizing the angular deviation between the reconstructed and captured rainbows. Finally, both numerical simulations and experiments are carried out to evaluate the feasibility of the improved algorithm. The results show that the error of the inversion result of refractive index is of the order of magnitude 10−4, and the error of the mean diameter is better than 3 μm.

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