Study On Effects Of Nozzle Internal Thread Structure On The Jet

In this paper,the influence of nozzle internal thread structure on jet breakup process is studied by using the laser dynamic gas-liquid interface fluctuation analyzer,high-speed camera and Malvern laser particle size analyzer,etc.The fluctuation characteristics of the gas-liquid interface of the nozzle with internal thread structure are revealed,and the prediction model of the jet breakup length of the nozzle with internal thread structure is established.The specific contents are as follows:1.The laser dynamic gas-liquid interface fluctuation analyzer and high-speed camera were used to study the characteristics of the unsteady fluctuation of the jet interface of the threaded nozzle,such as amplitude and frequency.Within the range of this experiment,the Strouhal number Sr of liquid jet fluctuation of smooth nozzle changes little with Reynolds number Re,and the Sr of threaded nozzle increases significantly with the increase of Re,and the thread structure has a strong disturbance to the jet.This is because the boundary layer thickness gradually decreases with the increase of Re,and the thread structure extends out of the viscous bottom layer,causing disturbance to the jet flow and increasing the instability of the liquid jet flow.2.The high-speed camera and Malvin laser particle size analyzer were used to study the jet breakup length of smooth nozzle and threaded nozzle.The disturbance exerted by the thread structure on the jet will increase with the development of the jet,which will promote the jet break and shorten the jet breakup length.According to the experimental results,the trend of jet breakup length was divided into laminar flow region,transition region and turbulent region according to the magnitude of Re.The jet breakup length of the threaded nozzle could be significantly reduced under the condition of high turbulence,and the prediction model of the jet breakup length of the threaded nozzle in the corresponding region was proposed.At the same time,the flow atomization process of smooth nozzle and threaded nozzle was studied.K-H instability and R-T instability induced by aerodynamics was stronger than that of thread structure,and the average diameter of atomized droplet was more affected by the gas flow.3.The high-speed camera and dynamic surface tensiometer were used to study the process of jet break of surfactant solution.Under the experimental conditions,there is little difference in the jet morphology between smooth nozzle and threaded nozzle when the jet is located in the transition zone.In the turbulent region,there are obvious morphological differences.The solution smaller than the critical micelle concentration is affected by the Marangoni effect,and the jet surface is more smooth.However,for the solution larger than the critical micelle concentration,due to the dispersion of the surfactant in the form of micelles in the solution,the Marangoni effect of the jet is weakened,and the shape of the jet is similar to that of pure water,and the jet surface disturbance is very strong.