Numerical Simulation Of Two-phase Air-water Spray Based On Laval Effect

Coal is an important basic energy and raw material in our country.With the improvement of mechanization automation level in our country,the situation of coal mine safety production continues to improve steadily.The dust concentration in coal mine exceeds the standard seriously,which seriously endangers the health of workers.Spray dust control is the main technical measure of dust prevention in coal mine.Based on the analysis of atomizing principle and main performance index of nozzle,this paper analyzes the atomization effect of traditional pressure nozzle and Laval effect gas?water two?phase nozzle with different structure and working condition parameters by using Fluent numerical simulation software.(1)The principle of Laval effect nozzle atomization is to increase the nozzle airflow velocity through the laval effect,thus increasing the gas?liquid two?phase velocity difference.the broken droplets will be further atomized under the strong action of gas power to form a fine water mist.the principle of pressure swirl nozzle atomization is that the liquid is accelerated through the spin core and flies to the solid wall under centrifugal force to form a rotating cavity.the liquid is ejected at a higher speed relative to the surrounding gas,and the atomization of the liquid is realized by a strong shear action between the gas and liquid.(2)Compared with the arc structure Laval nozzle,the conical structure has lower airflow velocity due to the blocking effect of shock wave on the airflow.The length of the contraction section,the length of the expansion section,the diameter of the throat and the angle of the half?cone are determined respectively.(3)The liquid pressure,gas-liquid pressure ratio,and the half?cone angle of the expansion section are the main factors affecting the atomization effect of the laval effect nozzle.With the increase of liquid pressure,the particle size of droplet increases;with the increase of gas?liquid pressure ratio,the particle size of droplet decreases gradually;the velocity of air flow at the outlet of nozzle increases gradually in the range of 8°~10° of half cone angle,and tends to stabilize in the range of11°~15.(4)Compared with the traditional nozzle,the two?phase nozzle with Laval effect has a better effect of spray dust removal.The total dust concentration and exhumation concentration of air entry lane distance,return air lane distance and the measuring point at the transfer machine have been greatly reduced.