March 10, 2022

The atomization process and principle of industrial nozzles

The atomization nozzles used by industrial nozzles in the field of atomization, and the atomization technologies of nozzles are also divided into many types. The working principles of atomizing nozzles cover almost all industrial fields. In industrial applications, we can understand how important the use of atomizing nozzles is, because atomizing nozzles can effectively dedust and purify the environment, humidify and cool industrial processes, etc. With the versatility of atomizing nozzle applications. The family of atomizing nozzles has gradually grown. This article introduces the differences and characteristics of the four types of atomizing nozzles that are often used in high pressure. Different atomizing nozzle characteristics lead to different industrial effects.

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First. The atomization process of industrial atomizing nozzles

The atomizing nozzle, as the name implies, is to pressurize the liquid to form a mist-like structure when the liquid passes through the nozzle. When the liquid is pressurized, the nozzle is shot into the static or low-speed airflow at a high speed. Due to the different nozzle structures, the atomization process is also somewhat different. It is usually atomized by the following process.

1. The atomization process of the direct nozzle

When the liquid pressure rises and the spray velocity increases, under the interaction of the liquid surface tension, stickiness and air resistance, the liquid transitions from dripping, smooth flow, and wavy flow to spray flow, and the spray velocity (that is, the flow rate) increases. The changing state of the length of the liquid column in the above-mentioned liquid flow state. The Reynolds number RE=1800-2400 for transition from migration flow to wavy flow to the turning point is consistent with the turning point of laminar flow and turbulent flow (turbulent flow). And the turning RE of viscous liquid is ≥ 3000 to form spray flow.

2. Centrifugal nozzle liquid film jet atomization process

The atomization process of swirl pressure atomizing nozzles (or centrifugal nozzles) under different oil pressures. Under low oil pressure, the injection speed is small, mainly due to surface tension and inertial force. Although the surface tension overcomes the inertial force, the liquid film shrinks into a bubble, but it is broken into large droplets under the action of aerodynamic force. As the pressure increases, the jet velocity increases, and the liquid film becomes unstable under the action of inertial force. Broken into a wire or ribbon, the relative movement with the air is violent, the effect of surface tension and viscous force is weakened, and the length of the liquid film is shortened. And twisted, broken into small mist droplets under the action of aerodynamic force. Under higher pressure (3.0MPa), the liquid jet velocity is larger, and the liquid film is atomized when it leaves the nozzle.
Generally, the centrifugal nozzle can be put into the combustion process when the pressure is 0.3-0.5MPa, that is, there is a part of the liquid film at the nozzle outlet. In the study of the above-mentioned atomization process, it was found that the smaller the surface tension of the liquid, the thinner the liquid film could be, to form fine filaments, ribbons, and to condense into fine droplets. The viscosity has the effect of hindering the crushing. It is also found that the viscosity of the liquid has an effect on the swirl tension of the liquid in the swirling flow. When the viscosity is low, the tangential and radial speed in the swirl chamber increase, and the atomization quality becomes better. In the middle stage of atomization, surface tension plays a major role, that is, affects the liquid film. In the later stage of atomization, the viscous force, surface tension, inertial force of oil droplets and air resistance interact to make the droplets further.

3. The atomization process of the rotary atomizing nozzle

The liquid is supplied to the center of the high-speed rotating part, and the liquid is thrown out to the periphery or the hole of the rotating part. It is a rotary atomization that atomizes the liquid with centrifugal force and aerodynamic force. When the liquid flow rate is very small, when the centrifugal force is greater than the surface tension of the liquid, a small amount of large droplets thrown from the edge of the turntable will directly become droplets at this time. When the flow rate and rotation speed increase, the liquid is pulled into a large number of filamentary jets, and the liquid flow is extremely unstable, and will separate into small droplets at a certain distance from the edge of the disk. This is the filamentary splitting into droplets. When the speed and flow increase again. The liquid filaments are connected to form a thin film, and as the liquid film expands outward into a thinner liquid film, it is ejected at a high speed, and is separated and atomized by friction with the surrounding air. From thin films into droplets. It can be seen from the above process that rotary atomization includes the interaction of centrifugal atomization and velocity atomization. The above two methods of atomizing liquid by means of external power (boosting the oil pump and increasing the motor speed) are collectively referred to as mechanical atomization. The centrifugal pressure atomization and rotary atomization both rely on centrifugal force. However, a small amount of atomizing air is also used on the rotating cup-type rotary atomizing device, which can further atomize the droplets.

4. The atomization process of the medium atomizing nozzle

With the help of high-speed coaxial or vertical high-speed jets of fluids such as air or steam, the liquid column or liquid film of the amnesty working medium is atomized. They are collectively referred to as dual-fluid atomizing nozzles, also known as hook pneumatic nozzles and air atomizing nozzles. Their atomization essence is similar to the aforementioned pressure atomization process, except that the effect of the surrounding airflow is enhanced. It uses high-speed, generally tens of meters per second, or even supersonic air or steam, and the liquid column or liquid film of low-speed liquid to collide and rub against each other, and break into fine droplets, that is, the external force (impact, friction) is greater than the oil. The internal force (surface tension and viscous force) to break the stream or liquid film.

Second. the working principle of industrial atomizing nozzle

The working principle of the industrial atomizing nozzle is to squeeze the internal liquid into the nozzle through the internal pressure, and a blade is placed inside the atomizing nozzle. To form a spray, the size of the nozzle blade is thin and thin. The diameter of the nozzle hole of the atomizing nozzle makes the liquid impact and rebound and split into atomized particles with a diameter of about 15-60 microns, which are sprayed through the outlet of the atomizing nozzle to form a fine atomized spray.

Third. the use of industrial atomizing nozzles

1. How to use the fan nozzle

The fan-shaped liquid is sprayed in a fan-shaped manner, and the impact force is larger than that of the hollow cone and the solid cone. In order to obtain a more even flow distribution when installing several fan-shaped nozzles, the distribution design is generally a mountain-shaped distribution. Flow distribution, spray height, distance between installation positions, spray pressure and the nature of the liquid are different. If there is an upstream error in the performance of multiple nozzles, the design value will not be consistent with the actual value. Therefore, the company has nozzles with sufficient accuracy to ensure a balanced traffic distribution.

2. How to use the hollow cone nozzle

Under the same nozzle pressure, spray flow rate and spray angle, the average particle size of the hollow cone nozzle is the smallest, and the average particle diameter is the smallest, which increases the surface area of ​​the workpiece and makes it more delicate. Movement has a greater impact, and hollow cone nozzles can produce good results in gas cooling, air humidification, metal processing, dust control, gas cleaning and chemical reactions. In the hollow conical nozzle, because the liquid is ejected through a single hole and several centrifugal action, it has the largest unobstructed diameter. It is an ideal choice for liquids that are prone to sedimentation, which can minimize the blocking phenomenon. produce.