Study Of The Purification Of High Salinity Water By Humidification Dehumidification Desalination Technology And The Saline Droplet Impact Dynamics Of Its Process

The treatment of high salinity water is a widespread concern in academia and industry.A small-scale desalination system was presented based on humidification-dehumidification(HDH)process.The feed salinity was changed to measure the performance in this experiment.This desalination system adopted the method of sprayed with high salinity feed water,and there were tens of thousands of saline droplets impacting on the packings surfaces inside the humidifier chamber.In addition,combined with the result of the HDH experiment,the spreading characteristics of saline droplet impacting on plate surfaces were observed and recorded with a high-speed camera,and the effect of salinity on HDH desalination system was further analyzed.The feed salinity had a significant effect on the performance of the HDH desalination system.The presence of Na~+and Cl~-in the feed changes the physical properties of the water,and the vapor pressure of the salinity water is lower.The reduction in vapor pressure directly reduced the power of water vaporization and reduced the amount of water vapor that can enter the circulating air.The result of the experiment indicated that the productivity decreased and the specific thermal energy consumption increased significantly with the increasing of the feed salinity,but this effect will not reduce the quality of the pure water,all the tests yielded very high salt rejection ratios(>99.9%).For saturated brine,the increase of feed flow rate had slight effects on the gained output ratio and the specific thermal energy consumption.The high-speed camera was used to analyze the characteristics of saline droplet impacting on the surface of PP plate.With the feed salinity increasing,increasing of viscosity and surface tension will hinder the saline droplet spreading and the liquid film will become smaller on the surfaces of the PP packings in humidifier.The increasing of salinity will decrease the gas-liquid contact area,which weakened the humidity ratio of the circulating air indirectly.The reduction of the liquid film with the increasing of feed salinity was an important factor that decreased the performance of the HDH desalination system.The increase of impacting velocity will promote the faster and larger spreading of the liquid film,and the larger spreading diameter that can be achieved.A smaller diameter will facilitate droplet to overcome the disadvantages due to increased salinity compared to a larger diameter droplet.In this paper,the dynamic characteristics of droplet with different salinity impacting on different wettability surfaces were investigated experimentally.As the wettability of the impact surface decreases,the energy loss on the hydrophobic surface becomes lower.The effect of salinity will be more obvious on the hydrophilic surface as it hinders the droplet spreading process.In addition,the main factor that affected the rebound or splash after the droplet impacting on plate surface was the surface wettability.When the droplet impacting on the superhydrophobic surface,secondary droplets with smaller diameter will be produced,and a large number of small droplets will increase the gas-liquid area in the humidifier chamber from another angle.Due to the high specificity of the inorganic salt content of feed water,the hydrophilic packings can increase the wetted area of the liquid film,but the risk of scale formation on the packings surfaces is increased.The wetted area of the hydrophobic packings will reduce,but the droplets pulverization effect will increase,and the risk of surface scale formation is relatively lower.When the HDH desalination technology will be used to desalinate the high salinity brine,the selection of the humidifier packings is very critical and deserves further exploration.