Investigation Of Self-calibrated Global Rainbow Technique And On-line Measuring Probe Development

Liquid atomization is a widespread phenomenon in the fields of energy and chemical industry.In many industrial applications,spray droplets play a leading role in the process of heat and mass transfer.Accurate measurements and controls of key parameters of droplets in the gas-liquid two-phase flow play an instructive role in the mechanism study of multiphase flows and in the optimization of a specific industrial process.Among the advanced optical measurement techniques for characterizing droplets,rainbow refractometry has been shown to be a powerful tool for its advantages in simultaneously measuring the size distribution and temperature or concentration.In recent years,a lot of important achievements in combustion,pollutant removal and other aspects of application research has been made by using rainbow refractometry.In this paper,the global rainbow refractometry is taken as the research subject.A self-calibration method based on dual-wavelength lasers for global rainbow refractometry is proposed.And a portabal global rainbow measuring probe with variable working distances is designed.In order to match the probe,an online measurement software is developed by conbining the online measurement and data management functions.In this paper,the following three aspects were studie。According to the deviation of the refractive index of the medium at different wavelengths corresponding to the deviation of the rainbow angle,a high-precision self-calibration method for scattering angle of global rainbow based on dual-wavelength lasers is presented.The specific processing steps and the algorithm flow are aloso given.Based on a hypothetical calibration medium temperature T and value of RI,the final calibration equation is determined by continuously iterating to find the minimum RMS deviation between the two wavelength refractive indexes and the inversion refractive index at the hypothetical temperature.The simulation results show that the RMS error between inverse refractive indices and hypothetical refractive indices is significantly decreased when the tested temperature T and the value of RI are close to the target ones.The dual-wavelength global rainbow measurement system was set up and deionized water was used as the calibration medium.The mean temperature and calibration parameters were measured.The refractive index of ethanol-water solution with gradient concentration of 10%～60%was measured by the dual-wavelength self-calibrated rainbow system.The results were compared with those of the inversed results by conventional mirror calibration method and the theoretical data for yellow light.The results of simulation and experiments show that the accuracy of self-calibration rainbow system can reach the precision of rainbow inversion algorithm.The self-calibration method spares the rainbow refractometry from extra angle or temperature measuring instrument.It enables the rainbow refractometry to be implemented in a more powerful and convenient way,and it may even be extended to calibration for one-dimensional rainbow technique.Based on the geometrical optics,this paper analyzes the principle of several rainbow scattering measurement systems and explores further.A double-lens portable global rainbow on-line measuring probe was designed and developed.The design of the optical path of the double lens combining a camara shot is a simple optical system with nearly fixed axial position of all the optical components.In order to achieve the purpose of multi-object distances measurement,the rainbow measuring probe can change the object distance by changing the front lens with different focal length.The positions of other components and the overall length of the probe is unchanged.By adjusting the multi-function rotary regulator,variety of operating modes can be quickly switched.It is beneficial to on-line engineering measurement applications by using the flexible adjustment of layout.The multi-range measurement system of the rainbow probe was set up,and a complete rainbow optical path adjustment,constant focal length of the fixed-focus lens,position of the laser,and scattering angle calibration were all carried out.The advice on the optimal working distance less than 30cm was givin by repeated tests and spray measurements under different object distances.The binary component spray of ethanol and water was measured by this probe system.The obtained rainbow curve coincided well with the fitting curve obtained from the inversion calculation.The measured values were in accordance with the literature values.For the supporting software of rainbow measuring probe,the problems that need to be solved during the actual field measurement and software operation were analyzed.The whole experimental process of the global rainbow measurement method and the follow-up data process were figured out.The MVC software architecture was detailed illustrated with business processes,functional modules,and other forms.The signal processing flow and the inversion algorithm were briefly introduced,and the related functions and performance are optimized for online measurement.The software requirements of the two scenarios of laboratory and industrial field measurement are considered synthetically.CCD control,the data real-time processing,the highly effective and easy to use operation flow,and the unified document management mechanism are integrated.Under Windows platform,Qt Creator is used to design and develop a full-featured,high-availability,high-precision and high-stability rainbow probe measurement software.The welcome and main interfaces and the page jump logic were analyzed,and the eight core functions were introduced in detail,such as the CCD control,signal acquisition,signal processing,parameter adjustment,data manipulation,file management,real-time inversion,and off-line processing.After several online and offline software testing,the real-time online measurement results of rainbow measurement probe have been verified.The measurement error,the main functions and the performance of the software are also analyzed.