| Water is an essential resource for human survival and development,which plays an important role in industrial,agricultural production and people’s daily life.Although water resources on Earth are abundant,the available freshwater resources for drinking are very scarce,which makes great attention should be paid to it and it should be utilized rationally.Furthermore,due to the increased awareness of people’s health and continues concern for water quality,as well as the improvement of national standards for water quality,the technology and requirements for domestic water treatment are becoming more and more stringent.The treatment of low-temperature and low-turbidity water becomes especially difficult in the severe cold winter.The conventional technology for water treatment is often ineffective and the desired result cannot be achieved which specialized research should be conducted.The pressurized dissolved gas flotation technology is applied to the treatment of low-temperature and low-turbidity water,and the generation rules and influencing factors of micro-bubbles under different process and geometric conditions were studied through simulation and experimental methods in this article.Firstly,the analysis of dissolution process and mechanism of gases in water was conducted theoretically.The gas is dissolved in water due to the combined action of interstitial filling and hydration,and the influence of either mechanism varies with temperature.The interstitial filling plays a dominant role when the temperature is above 50℃,while the effect of hydration is dominant when the temperature is below 50℃.The low-temperature and low-turbidity water studied in this paper is below 10℃ which belongs to the latter case,so hydration plays major role in the dissolving process of air.Then,the changes of the internal flow field of the releaser were studied,and the influence of different pressures and the outlet diameter of the releaser on the internal flow field of the releaser was studied through simulation.It can be observed that the pressure difference and velocity difference increase with the enlargement of releasing pressure,which can produce finer micro-bubble in consequence;the larger the outlet diameter of the releaser,the greater the pressure and velocity difference in the chamber under certain initial pressure,which makes it easier to generate micro-bubbles with smaller particle size and greater quantity which is more applicable to the gas flotation.Finally,the formation process of micro-bubbles under different process characteristics and geometric characteristics was experimentally studied,and the influence of different dissolving pressures and releaser outlet diameters on the formation size of micro-bubbles was analyzed.The average diameter of the generated micro-bubbles decreases as the pressure increases with specific outlet diameter of the releaser,and the average diameter of the micro-bubbles changes slightly when the releasing pressure maintains to a certain value.Under certain releasing pressure,the average diameter of the generated micro-bubbles decreases with the increase of the releaser’s outlet diameter,and the average diameter of the micro-bubbles keeps invariable basically with certain outlet diameter of the releaser.The larger dissolving pressures and releaser outlet diameters make it easier to generate micro-bubbles that meet the requirements of the air flotation process,which is consistent with the results of the simulation.Through the theoretical and experimental research mentioned above,the size of micro-bubbles generated through pressurized dissolved gas flotation and related influencing factors were analyzed and demonstrated,and the releasing law and influence factor on the generation of micro-bubbles from water under low-temperature and low-turbidity condition were concluded,which can provide basic reference and theoretical basis for the adoption of the pressurized dissolved gas flotation technology to the treatment low-temperature and low-turbidity water. |
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