Design And Experimental Study Of Atomization Wide Spray Valve Based On The Gas-liquid Two-phase Mixing

With the continuous updating g and rapid development of electronic products,the traditional coating technology can not meet the technical requirements of modern technology.The selective coating process has obvious advantages over other processes: With a wide range of coating viscosity;Selective coating on demand;Controllable spraying width and thickness and other characteristics.Therefore,the world famous dispensing coMPanies have developed selective coating equipment.However,the existing selective coating equipment can only achieve narrow-range coating.At present,little research has been done to complete a wide-range of coating.A wide-range of coating operation can greatly improve production efficiency.The coating operation is required many times of back and forth coating by the original coating equipment.But now it can be completed only once.And the wide-range of coating operation,which can also be used in paper industry,phone box packaging industry and so on.It can solve the environmental pollution problems caused by the existing traditional dyeing spraying equipment.In order to achieve selective coating in different applications areas,which is narrow-range coating and wide-range coating,an atomizing spraying idea based on the principle of gas-liquid two-phase mixing is proposed in this paper.And according to the different principles of the internal and external atomization,the internal atomizing spraying valve with a spray nozzle,the external atomizing wide spraying valve and the internal atomizing wide spraying valve are designed and optimized.Finally,experimentally,the influence of the working parameters of the equipment on the atomization effect is discussed and particle size measurement is carried out under the internal and external atomization conditions.The main research contents as follows:1?Study on liquid atomization mechanismThrough the study of the principle of liquid atomization,it is known that when the liquid column breaks up and splits into smaller droplets,it needs to undergo the first-order atomization and the second-order atomization in the process of gas-liquid two-phase mixing.When the gas dynamic force from the outside world is greater than the viscous force and surface tension of the liquid itself,an unstable surface wave would be form on the surface of the liquid.The continuous action of gas dynamics force will make the fluctuation of the unstable surface wave more intensely,and eventually force the liquid column split into atomized particles.It is shown that the structure of the flow passage,the pressure difference between the gas and liquid and the physical properties of the gas and liquid are the key factors affecting the liquid atomization by an analysis of the atomizing principle.The formed atomized droplets will continue to collide due to the difference of their kinetic energy.Thus,the critical criterion for collision between droplets and three indexes for indicating atomization effect are established in this paper: an atomizing angle,an atomizing particle size(Sauter mean diameter SMD)and an atomizing uniformity.The mathematical model of SMD for indicating the atomization effect of liquid is established.Then,the relationship curves of gas flow rate,liquid flow rate,gas-liquid volumetric flow ratio and liquid viscosity with the SMD of atomized droplets were obtained.2?Design and development of atomizing spraying control systemA control system is designed and built to drive the coating operation of atomizing spraying valves by using single chip computer.For the three atomizing spray valves in the paper,three corresponding spray control schemes and response time sequence charts are proposed.Finally,the DC motor model which drives the motion of rotation axis is selected reasonably and the connection between the modules needed to drive the motion of rotation axis is established.3?Design and experimental test of the internal atomizing spraying valve with a spray nozzleThe nozzle structure of the internal atomizing spraying valve with a spray nozzle is optimized.The coordination mode of the gas-liquid passage was determined as the cone-cone way and the key parameters were determined,thus,ensure the uniformity of gas flow rate.Structurally,the response structure of a needle switch is used to design the selected coating internal atomizing spraying valve.And the experimental test system of this valve is established.Experimentally,the effects of working parameters such as supply gas pressure,supply liquid pressure,liquid viscosity and spraying height on spraying effect are tested and analyzed.The result show that with the increase of supply gas pressure,the coating width and thickness increase first,then decrease,and decrease continuously,respectively.With the increase of supply liquid pressure,the coating width and thickness increased first,then decreased,and gradually increased,respectively.With the increase of the liquid viscosity,the coating width and weight all decreased gradually.With the increase of spraying height,the coating width increased first,then gradually tends to a steady state.4?Design and experimental test of the external atomizing wide spraying valveIn order to realize wide-range coating and based on the spraying characteristics of larger atomization angle by the external atomization,a design scheme of the wide-range coating by the external atomization is proposed,and in order to achieve a wide-range coating,a design scheme of multi-nozzle is adopted.The structure model of the external atomizing nozzle and its key structure parameters are determined by software.At the same time,the uniform liquid plate and the uniform air plate are adopted in the structure design,which makes it easier for the equipment to obtain uniform liquid flow rate and gas flow rate at the every sprinklers head.The bottom-up way is used as the supply liquid way.Thus,the premise of precise atomization is guaranteed comprehensively.The experimental test system of this external wide-range coating valve is established.The effects of working parameters such as nozzle diameter,supply gas pressure and supply liquid pressure on external spraying effect are tested and analyzed.The result show that with the increase of nozzle diameter,the atomized particle diameter and coating width increased and increase first,then decreased,respectively.With the increase of supply gas pressure,the atomized particle diameter and coating width decreased,and increase first,then gradually tends to a steady state,respectively.With the increase of supply liquid pressure,the atomized particle diameter and coating width increased and decreased,respectively.At the same time,the coating test of this valve is carried out when the substrate is cloth.The experimental results show that the differences between dark and light colors and color difference of cloth under different conditions also can further prove the rationality of the previous experimental test and theoretical analysis.5?Design and experimental test of the internal atomizing wide spraying valveBecause the cross area of multi-nozzle atomization angle is easy to appear on the process of multi-nozzle external atomizing work,the atomized particles in the cross area overlap with each other,and the coating thickness at different positions on the same line is not uniform.However,internal atomization is easy to achieve good atomization effect because it is completed in its own atomization chamber.Therefore,an internal atomization wide spraying idea with better uniformity and wider coating width is proposed in this paper,and the structure of the liquid and gas chambers is determined to be ladder-shaped.The structure of rectifier plate is designed in the gas chamber.Thus,the consistency of liquid flow rate and gas flow rate at the outlet of each flow passage of the atomizing equipment is guaranteed comprehensively.The design of rotating shaft can make the gas-liquid two-phase mixing uniformly in the atomization chamber and form smaller droplets more easily.The experimental test system of this internal wide-range coating valve is established.The effects of working parameters such as supply gas pressure and supply liquid pressure on internal spraying effect are tested and analyzed.The result show that with the increase of supply gas pressure and supply liquid pressure,the atomized particle diameter decreased and increased,respectively.Finally,the PDPA test system is set up to test and coMPare the atomized particle diameter formed under the condition of internal and external atomizing wide spraying valves.The result shows that the internal atomizing wide spraying valves has smaller particle size and better coating uniformity than the external atomizing wide spraying valves.