1. Pressure type nozzle
When using pressure atomizing nozzle (direct and centrifugal) to carry out spray dustfall, the dust removal efficiency depends mainly on the water supply pressure, and the water pressure of different particle sizes is different for the definite use occasions. The higher the pressure of the finer dust is, the higher the pressure is. High water supply pressure can not only obtain fine water mist, but also make the water mist particles move faster and contain more water in the space, which is very beneficial to the dust reduction method based on collision mechanism. According to the actual dust particle dispersion and dust reduction efficiency requirements, referring to the corresponding curve to select the appropriate water pressure can achieve good results and good economic benefits. The conclusion is applicable to any workplace where pressure atomizing spray nozzle is used to spray and settle coal dust.
2. Two phase nozzle
For the two-phase nozzle, the atomization ability is affected by the following factors:
(1) Influence of mixing pipe diameter and length
Smaller inner diameter of mixing tube can increase the relative velocity of gas-liquid two-phase, which is conducive to atomization, but it will affect the re aggregation of atomized particles. Because the mixing pipe is too long, the gas energy loss is too much, so the liquid flow atomization will become worse; if the mixing pipe is too short, the gas energy can not be fully utilized, resulting in insufficient liquid flow atomization.
(2) Influence of nozzle
Because reducing the outlet area will increase the outlet pressure drop, the acceleration effect of gas-liquid mixture will be significantly enhanced, and the relative velocity of gas-liquid mixture will increase, which will also make the liquid phase break finer. However, the increase of the outlet pressure drop will inevitably increase the pressure in the mixing pipe, resulting in the decrease of the relative velocity of the gas-liquid two-phase in the mixing pipe, which will make the atomization worse.
(3) Relationship between gas liquid ratio and atomization particle size
With the increase of gas-liquid ratio, the atomization particle size decreases. Therefore, increasing the gas-liquid ratio can increase the relative velocity of gas-liquid two phases and make the liquid film break more finely. However, when the gas-liquid ratio increases to a certain extent, the change of particle size is not obvious.
(4) Variation of droplet concentration with gas-liquid ratio
With the increase of gas-liquid ratio, the particle concentration of water decreases, which is caused by the decrease of water mass fraction in air.
3. Ways to improve atomization of nozzle
According to the atomization mechanism and experimental research, combined with the coal mine field experience, the main ways to improve the atomization are as follows:
(1) By increasing the relative velocity difference of gas-liquid two-phase, the aerodynamic force is increased, and the droplets are broken more finely than the atmospheric force.
(2) In order to enhance the collision, the exit velocity of the liquid nozzle is increased, so that the relatively ejected droplets can be further broken during the collision. It is found that if the droplet outlet velocity is small, it will converge into large droplets. If the droplet outlet velocity is large, it can improve the degree of atomization. However, this will reduce the relative velocity of gas and liquid and make the aerodynamic atomization droplets worse.
(3) The experimental results show that the geometry and size of nozzle and mixing tube have great influence on the atomization performance. Therefore, in the design of the model, in addition to considering their influence on the atomization, we should also consider the change of the overall performance after they are combined.
(4) to study the relationship between the flow and pressure of the spray water supply system and the nozzle geometry and the shape of the structure, so as to improve the atomization effect. The higher the water pressure, the finer the water mist particles. However, the problems caused by higher water pressure are: a. large energy consumption; b. all parts in the water supply system are subjected to high pressure, easy to break down and short life span, especially the internal spraying system on the mining equipment. This brings us another research topic: how to improve the structure of pressure atomizer to obtain fine water mist particles under limited water supply pressure.
Through the analysis of the classification and characteristics, the application scope of various types of nozzles is pointed out. Based on the analysis of the factors affecting the atomization ability of nozzles, the ways to improve the atomization effect of nozzles are put forward. In order to improve the atomization effect of the nozzle, the characteristics of the nozzle and the water supply system must be matched, simultaneously improving the water quality and improving the filtering accuracy of the spray water.
