Calculation and Numerical Analysis of the Nozzle Orifice Flow Model in the Process of Vacuum Jet Atomization
In the process of preparing the thin film by the vacuum jet method, the jet effect mainly depends on the structure of the nozzle. Different nozzles have different effects on the atomization of liquid jets, and their effects mainly depend on the shape of the nozzle in the nozzle. The flow model and numerical analysis of the three different nozzle nozzle shapes show that the volume of water vapor in the cone-shaped nozzle The score change is small, the atomization effect is the best and the quality of the film formation is the highest.
The vacuum jet atomization process is the main film forming process of the vacuum jet method to prepare polymer films. This method mainly uses the large pressure difference between the vacuum chamber and the outside to make the polymer solution sprayed and atomized through the nozzle and dispersed into countless high-speed motions The fine droplets reach the substrate to form a polymer film. The quality of the film formation mainly depends on the quality of the spray. The primary factor that affects the spray quality is the nozzle. Different nozzles have different droplet spray characteristics depending on the structural parameters and spray environment.
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In the study of the numerical simulation of the preparation of polymer thin film spray by vacuum jet, the flow analysis inside the nozzle provides the initial conditions for the jet atomization after the liquid exits the nozzle, such as the spray velocity distribution, the spray cone angle and the droplet diameter distribution. Due to the complexity of the flow inside the nozzle, it is difficult to measure it experimentally. Due to the occurrence of cavitation and backflow in the process of liquid flowing through the nozzle, it has a greater impact on the flow state of the nozzle outlet, so it is very necessary to analyze and simulate the internal flow of the nozzle.
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Nozzle nozzle flow model
Existing models of the internal flow state of the nozzle that have been widely proven and recognized by everyone are summarized on the basis of the experimental observations of the enlarged and real nozzle internal flow by Soteriou and Chaves, etc., mainly including single-phase flow, cavity flow and hydraulic The three flow states of reverse flow are schematic diagrams of the flow states in the nozzle. In the single-phase flow state, the ejected liquid fills the entire nozzle without any gaps. At this time, the flow is laminar or turbulent. The flow loss of the liquid mainly comes from the friction with the nozzle wall and the contraction caused by the sudden change of the interface at the nozzle. And later expansion. The liquid initially flows out in the form of a single-phase flow, and on the basis of its full development, with the increase of the jet speed, when the Reynolds number reaches a certain value, the static pressure in the nozzle contraction area decreases, and when the static pressure in this area drops to the liquid saturation When the vapor pressure is below, cavities will be generated on the nozzle wall. When the cavities fill the entire nozzle wall area, it is a cavitation flow.
Cavitation flow is the most common flow state that occurs when the nozzle flows. With the further increase of the jet speed, if the nozzle is an ideal nozzle with a smooth wall and axial symmetry, the cavities in the downstream continue to develop until it shrinks to the upstream of the nozzle, and the cavity area is connected with the outside air out of the nozzle to form a hydraulic force. Backflow. When the hydraulic backflow occurs, the liquid flows out smoothly in the form of a liquid column, and the jet liquid does not break until it is far from the nozzle. In actual spraying, the hydraulic backflow phenomenon can be ignored because the nozzle is not ideal. Cavitation flow is the most common flow state inside the nozzle.
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Calculation and Numerical Analysis of the Nozzle Orifice Flow Model in the Process of Vacuum Jet Atomization
Different flow conditions will determine different spray boundary conditions. Correctly judging the nozzle flow state has an important influence on the research of the liquid jet atomization process. The determination of the flow state needs to consider the following parameters: the number of holes (K), the flow coefficient (Cd) and the shrinkage coefficient (Cc) where the holes occur. The specific calculation formula is as follows:
Calculation and Numerical Analysis of the Nozzle Orifice Flow Model in the Process of Vacuum Jet Atomization
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Through the above analysis of the establishment of the model of the three different nozzles at the nozzle, the numerical analysis and simulation, and the determination of the nozzle parameters, it can be seen that among the three nozzle structures, the volume fraction of water vapor at the nozzle of the conical nozzle has the smallest change. . This will make the jet velocity and pressure distribution of the liquid ejected from the nozzle less change, the jet will atomize more fully under the disturbance of turbulence, and can form uniform small droplets to make the polymer solution on the substrate more distributed. It is easy to form a dense polymer film with stable chemical properties evenly.
Founded in 2015,Zunhua Baorui Titanium Equipment Co.,Ltd. is a manufacturer specializing in pvd vacuum ion coating equipment. The company’s products mainly include large plate coating machine, large tube collating machine, tool coating machine and LOW-E glass production line. Mr.Wang baijiang ,general manager of the company ,has been engaged in vacuum coating industry for more than 30 years. He continuously improve production technology, improve product performance and devote himself to provide customers with better product experience and higher production efficiency.