Study On Atomization Stability Of Two-fluids Based On High Speed Image-laser Diffraction Data Processing Technology

With the advancement and development of science and technology,modern industry has higher requirements for nozzles.Two-fluid nozzles,due to their ability to overcome the shortcomings of traditional nozzles and further improve spray quality,have emerged as a promising option.However,due to the introduction of gas phase and its interaction with the liquid phase in the mixing chamber,two-fluid nozzles inherently exhibit instability in atomization.In this study,experimental data and data processing techniques were combined to systematically investigate the influence of different operating conditions on spray stability for two-fluid nozzles,which has significant practical implications for the development of two-fluid nozzles.This article focuses on a typical two-fluid nozzle with internal mixing as the experimental research object.High-speed cameras were used to capture the liquid fragmentation morphology near the nozzle outlet,and the stability of the spray in the symmetric morphology was analyzed based on the average image and root mean square image of the spray.The spray average image is the image obtained by averaging the corresponding pixel points of multiple images,while the spray root mean square image is the image obtained by solving the root mean square.The results show that when the liquid flow rate is low,the stability of the spray increases with the increase of air-liquid mass ratio（ALR）,but the opposite is true when the liquid flow rate is high.Similarly,when ALR is low,the stability of the spray increases with the increase of liquid flow rate,but the opposite is true when ALR is high.In addition,the spectral analysis of the average grayscale sequence and grayscale centroid sequence was combined to analyze the stability of the spray in the axial and radial fluctuation morphologies.The results show that when the liquid flow rate is low,the axial and radial fluctuations of the liquid increase first and then decrease with the increase of ALR,and the same trend is observed at high liquid flow rate conditions.Under small and medium ALR conditions,the axial fluctuation of the liquid increases with the increase of liquid flow rate,while the radial fluctuation shows the opposite trend.Under large ALR conditions,the axial fluctuation of the liquid increases first and then decreases with the increase of liquid flow rate,while the radial fluctuation decreases continuously.The study also found that the axial fluctuation frequency of the liquid at different axial distances is almost the same,and the same is true for the radial fluctuation frequency,but the amplitude increases with the increase of axial distance.When ALR is large,the main frequency of axial and radial fluctuations of the liquid is almost the same,but the amplitude of axial fluctuation is significantly larger than that of radial fluctuation.In this study,a Malvern laser particle size analyzer was used for high-frequency sampling to obtain spray droplet size data,and several indicators for evaluating data stability and dispersion were compared and analyzed.In the time domain,the coefficient of variation was chosen to process the experimental data,and in the frequency domain,fast Fourier transform was used to analyze the experimental data,in order to explore the effects of different operating conditions and axial positions on spray stability.The results show that,overall,small droplets had the best stability,followed by medium-sized droplets,and large droplets had the poorest stability.The spray stability was strongest at medium liquid flow rate and medium to large air-to-liquid ratio（ALR）conditions.With increasing axial distance,the stability of small and medium-sized droplets gradually increased,while the stability of large droplets decreased.The fast Fourier transform results of droplet size data show that,when keeping the liquid flow rate and changing the ALR condition,the change in the magnitude of the main frequency amplitude in the frequency spectrum was relatively large,while the change in the main frequency was relatively small.When keeping the ALR condition and changing the liquid flow rate,the frequency of the main frequency always increased with increasing liquid flow rate,while the amplitude of the main frequency did not show a clear pattern of change.The frequency spectrum shapes obtained from fast Fourier transform of D_0.1 and SMD（Sauter Mean Diameter）data were very similar,but the amplitudes corresponding to each frequency were different.When the spectrum shapes were similar,the influence of the amplitude of the main frequency was greater than the influence of the frequency,and greater than the influence of other frequencies.