The Preparation Of NaCl Aerosol Partial By Droplet Evaporation

The preparation of sodium chloride aerosol is an important research field in aerosol science and technology. It has been widely used in experimentation,medical treatment and many other aspects.In this experiment, the liquid atomization is used to made sodium chloride aerosol. The process is mainly made up of spray,heating and evaporation. The mechanism of sodium chloride aerosol formation and the effect of gas flux, solution concentration on the particle-size distribution are firstly discussed theoretically and experimentally. Our work in this paper can provide a useful method to produce different kinds of sodium chloride aerosol.In order to get appropriate spray, two-phase nozzle is selected. There are two thin pipes for air inlet and one thick pipe for water inlet in the nozzle. The thin pipe is linked to thick pipe in 30°. In this way, when the solution is impacted by the air, both the axial speed and radial speed can be produced along the thick pipe. The shear stress caused by the radial speed forces the liquid spray all around the tip of the nozzle due to the surface tension to form rotary streams. When the mixture of the air and the water comes out from the nozzle, the fine droplets can be generated by the pressure difference between the inside of the nozzle and outside of the atmosphere. At the mouth of sprayer, the external force around the droplet is much bigger than the internal force, which makes the droplet split ceaselessly. The diameter, mass, surface area of the droplet minish gradually until the external force is equal to the internal force.When the gassy flux is100L/min, initial temperature is 30℃, the internal mural temperature of circular pipe is 200℃, the fluid state is laminar flow, suppose the droplet moves invariably in straight line in the heater, the mathematical expression of temperature field can be predigested 0 step Bessel function in the pipe. To establish the mathematical model about droplet evaporation, the relative motion between droplet and gas, as well as the heat convection were ignored. The function relation among the droplet diameter, the time of evaporation, the ambient temperature, and some other parameters had been developed. If the temperature is kept unchangeable, the complete evaporation time of the droplets with same size become shorter as the droplet velocity increases. If both the temperature and the velocity have no change, the larger the droplets, the longer the complete evaporation time is. The theoretical result has shown that the complete evaporation time of the droplet is proportional to the square of the drop diameter. Further more, if the velocity kept constant, the complete evaporation time will reduce as the ambient temperature increasing. All above theoretical investigations have got fairly good agreement with former researcher's experimental results.In the experiment for determining the effect of the solution concentration on the particle-size distribution of sodium chloride aerosol, the gas flow rate and the solution flow rate are taken as 6m~3/h and 20mL/min respectively. The concentration of NaCl solution is set up at 5.96g/L, 6.03g/L, 6.17g/L, and 6.30g/L. The experimental data from above four different conditions have shown that the particle size of sodium chloride aerosol increase if the concentration of the sodium chloride solution increases. At mean while, when the solution flow rate and concentration are kept constant, according to the experiment, the particle size of sodium chloride aerosol will be reduced if the gas flow rate is increasing.The final outcome of this experiment indicates that in the practical application of aerosol atomizer, the particle size and quantity of sodium chloride aerosol can be well controlled in a wide range by just changing the solution concentration, the gas flow rate, the operational parameter, and the structural parameter at a given solution flow rate.