What Is a Fog Nozzle?

Nozzles are one of the most important components of combustion equipment. Generally, nozzles are used for the combustion of liquid fuel. The quality of the nozzle design has a great influence on the combustion of liquid fuel. The function of the nozzle is to atomize the liquid fuel and form a liquid mist with a small diameter, so as to increase the contact area between the liquid fuel and the surrounding medium, and achieve the purpose of rapid evaporation, mixing and combustion. ^[1]

The methods of nozzle research are mainly test methods and numerical methods.

The cold simulation test method is currently the most important test method. Under cold conditions, water, air and other simulated media are used for testing, and optical instruments such as PDA are used for spray measurement. The flow characteristics, atomization characteristics and mixing characteristics of the nozzle are measured. research. The nozzle characteristics research under thermal test conditions is to visually observe the combustion flow field downstream of the nozzle through a transparent window, and to obtain the image of the nozzle atomization process and the droplet movement and component distribution in the combustion flow field through optical shooting.

With the development of CFD technology, numerical simulation of the atomization process has become an important emerging research method. Using

The research shows that the nozzle atomization process is mainly controlled by 4 kinds of forces, namely, aerodynamic resistance,

Atomization characteristics refer to the influence of nozzle structure, working parameters, physical properties of the atomizing agent and the atomizing medium on the atomizing performance of the nozzle. In order to comprehensively evaluate the atomization performance of the nozzle, a number of index parameters are proposed, mainly including: atomization fineness, atomization uniformity, and atomization cone angle. ^[4]

Classification by mist flow shape

According to the shape of the mist flow formed by the nozzles, the nozzles can be divided into two categories: cone-shaped solid nozzles and cone-shaped hollow nozzles. Solid nozzles are mainly for dust reduction, and hollow nozzles are for dust prevention.

The flow velocity of the cone-shaped solid mist column sprayed by the solid nozzle is relatively large,

Pressure nozzle

When using pressure-type atomizing nozzles (direct and centrifugal) to implement spray dust reduction, the dust reduction efficiency is mainly determined by the water supply pressure for certain applications. The dust pressure of different particle sizes is different, and the finer the dust pressure The higher. The high pressure of water supply can not only obtain the fine water mist, but also make the water mist particles move at a high speed and the water content in the space is large, which is extremely advantageous for the dust reduction method mainly based on the collision mechanism. According to the actual dust particle dispersion and dust reduction efficiency requirements, and referring to the corresponding graph to select the appropriate water pressure can achieve good results and the best economic benefits. This conclusion is applicable to any workplace where pressure-type atomizing nozzles are used to settle coal dust. ^[2]

According to the atomization mechanism and experimental research, and combined with the experience of coal mine field use, the main ways to improve the atomization of the nozzle are as follows:

(1) Increasing the relative velocity difference between the gas and liquid phases to increase the aerodynamic force, so that the droplets will be broken more finely under the action of a larger aerodynamic force.

(2) Increase the exit speed of the liquid nozzle to enhance the collision, so that the relatively discharged liquid droplets can be further broken during the collision. The experiment found that if the droplet exit velocity is small, it will aggregate into large droplets, and if the droplet exit velocity is large, the degree of atomization can be improved. However, this will reduce the gas-liquid relative velocity and make the aerodynamic atomized droplets worse.

(3) The experimental results show that the geometry and size of the nozzle and the mixing tube have a great influence on the atomization performance. Therefore, when designing the model, in addition to considering their impact on fogging separately, they should also consider the overall performance changes after they are combined.

(4) Investigate the relationship between the flow and pressure of the spray water supply system, the geometric size and the shape of the nozzle, and improve the atomization effect. In particular, the water pressure of the water supply system has a greater impact on the atomization effect. The higher the water pressure, the finer the water mist particles. However, the problems caused by higher water pressure are: large energy consumption; all parts in the water supply system are subject to high pressure, which is prone to failure and short life, especially the internal spray system on mining equipment. This brings us to another research topic: how to improve the pressure-type atomizing nozzle structure to obtain fine water mist particles under the limited water supply pressure. ^[2]

By analyzing the classification of nozzles and their characteristics, the applicable range of various nozzles is pointed out, and on the basis of analyzing the factors affecting the atomization ability of nozzles, a way to improve the atomization effect of nozzles is proposed. In order to improve the atomization effect of the nozzle, it is necessary to match the characteristics of the nozzle and the water supply system, and at the same time improve the water quality and the filtration accuracy of the spray water. ^[2]

The main difficulties of nozzle research

The predicament of nozzle research is mainly that the governing law of the nozzle atomization process is unclear. The physical model describing the atomization process is difficult to establish because it involves the process of continuous phase liquid transforming into a large number of discrete droplets. In addition, because the size is generally small, the flow process of the liquid medium inside the nozzle is complicated, which has a significant impact on the working performance of the nozzle. In addition, the actual nozzle atomization process often occurs in the combustion flow field, which brings great difficulties to experimental measurement. So far, the atomization characteristics of the nozzle under real combustion conditions have not been understood. ^[4]