| Gas-liquid two-phase flow atomising nozzles are the main atomising device for generating fine water mist and are already widely used in everyday life and modern industry.In order to reduce the droplet size of the nozzle,optimise the nozzle structure and enrich the application of two-phase flow nozzles in the field of environmental regulation.This paper designs a new gas-liquid two-phase flow three-stage atomisation nozzle based on the impingement flow atomisation technology and the Carmen vortex street atomisation mechanism.The atomisation breaking process of the internal and external flow fields of the nozzle under different operating pressures is studied,and the test scheme of the nozzle atomisation cooling is optimised by applying orthogonal tests.The main research contents are as follows.(1)This paper firstly conducts a theoretical study of the impinging flow atomisation mechanism and the vortex atomisation mechanism of the gas-liquid two-phase flow three-stage atomisation nozzle,followed by a brief introduction of the main influencing factors affecting the atomisation fragmentation of the nozzle and the main indicators for evaluating the good or bad atomisation effect of the nozzle,and finally a detailed introduction of the internal structure of the gas-liquid two-phase flow three-stage atomisation nozzle designed in this paper.(2)The atomisation characteristics and flow characteristics test platform is built,and the atomisation breaking mechanism and characteristics of the nozzle are studied experimentally under different operating pressures,and the liquid jet atomisation breaking process of the nozzle is observed under different working conditions.The results of the study show that the magnitude of the gas phase pressure has a significant effect on the nozzle atomisation and fragmentation mechanism.Gas-liquid two-phase flow three-stage atomisation nozzle external flow field spray pattern is not standard conical,in the XOZ cross-section and YOZ cross-section atomisation cone angle has a significant difference,and the nozzle atomisation cone angle,atomisation penetration distance,spray volume,flow rate,flow intensity distribution,with the change of operating pressure,a significant change.(3)A three-stage atomisation nozzle model for gas-liquid two-phase flow was established,and the VOF and VOF-to-DPM models in Fluent simulation software were used to simulate the internal and external atomisation breaking process of the nozzle under different operating pressures.Based on the vortex atomisation principle,three different types of vortex generators were installed in the external flow field of the nozzle and the atomisation performance of the original nozzle was compared and studied.The results show that: when Pair>0.3 MPa,the nozzle internal expansion type gas chamber structure can make the gas expansion accelerated to supersonic speed;when Pair≥0.2 MPa,the gas exit velocity on both sides of the nozzle also reached supersonic speed,indicating that the nozzle structure design is reasonable,the gas in the nozzle exit can produce a strong disturbance force on the liquid,so that it occurs atomization fragmentation.In addition,the VOF-to-DPM model and AMR technique can effectively capture the liquid atomisation breaking process and droplet flow.The original nozzle droplet D32 reached a minimum value of 9.89 μm when the gas-phase pressure was 0.6 MPa and the liquid-phase pressure was 0.2 MPa,while the improved nozzle reached 9.32 μm when the gas-phase pressure was 0.3 MPa and the liquid-phase pressure was 0.2 MPa,indicating that the nozzle structure improvement can effectively improve the nozzle atomisation performance.(4)A restricted space atomisation test platform was built to study the temperature and humidity variations in the test platform under different working conditions,and the optimal operation scheme was obtained through orthogonal tests.The results of the study show that the droplets produced by the gas-liquid two-phase flow secondary atomisation nozzle are large,the droplets are highly wetting,there is an obvious feeling of water droplets on the sprayed body,and water is easily formed on the ground.However,gas-liquid two-phase flow three-stage atomisation nozzle atomisation cooling effect is better than the traditional two-phase flow secondary atomisation nozzle.Dry mist cooling effectively improves the problem of water accumulation inside confined spaces,while improving the air quality inside the confined space.In addition,for the siphon type gas-liquid two-phase flow three-stage atomiser,the best atomisation cooling effect is achieved when the air pressure is 0.3MPa,mechanical ventilation(wind speed 3.4m/s),nozzle height 0.5m and spray angle 60°.(5)A three-dimensional model of the improved atomiser was established by Creo software,and the simulation clouds of the flow of gas and liquid in the three-layer flow channel of the new atomiser under different operating pressures were obtained by numerical simulation.The results show that the velocity and pressure distribution inside the three-layer flow channel of the new atomiser has good symmetry,and that the gas and water sources can be supplied to the eight nozzle connections quickly,uniformly and stably.The problems of unstable water supply and small pressure adjustment range of the original atomiser have been solved. |
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