The Formation Mechanism And Test Research Of Micro Gas Bubbles In One-component Dissolved Air Method

Air flotation technology is a kind of solid-liquid or liquid-liquid separationtechnology， and has been widely used in printing and dyeing， paper making， leatherproduction， oil refining， electroplating， chemical industry， chemical fiber， food andbeverage and other industries. The pressure dissolved air method is one kind of flotationprocess，with the micro air bubble having the characteristics of fine，uniform，dense，andsmall disturbance by liquid. Its principle is to combine the tiny air bubbles in the process ofrising with the impurity particles or flotation particles in the liquid phase， thus improvedparticle buoyancy and took it to the liquid surface， then using the slag scraping device toremoval. Studying on the size， quantity and energy consumption of the micro bubble isdirectly related to the cost and efficiency of air flotation technology， and the theoretical andexperimental research on the formation mechanism of micro bubbles has great practical andtheoretical significance.The most important inspect of air flotation is the size of micro-bubble. The releaseprocess study of one-component dissolved air (nitrogen and oxygen) is based on dissolved-airpressure， releaser shape， gas type. It will provide a reference and theory basis ofone-component dissolved air research.Firstly， this paper theoretically analyzed the mechanism of the gas dissolved in thewater， and obtained the proportion of nitrogen， oxygen in two kinds of dissolved formsunder different temperatures， to provide a theoretical basis for improving the efficiency ofdissolution; subsequently， studied the nucleation process of dissolved air gas and the wholeprocess of free-energy change， and got the parameters related its nucleation free energychanges.On the basis of these studies， the micro air bubble generating devices of oxygen，nitrogen， air in dissolved air method and bubble image capture devices were founded. Andsix micro air bubble releasers which with similar kind but different release angle weremanufactured. Each micro air bubble releaser as the variable of the test and the whole processes of the test were designed. Then the velocity field and pressure field of every grouptest were simulated by FLUENT which is a famous stimulation software. The simulationresults show that with the increase of releaser angle， the differential pressure and velocityrate become bigger and the size of micro air bubble become bigger either.According to the design plan of the test， when the release angle is constant， with theincrease of dissolved air pressure， the diameter of oxygen， nitrogen， air all becomebigger，but when the pressure beyond0.4MPa the growth rate decreased; when the dissolvedair pressure is constant， with the increase of release angle， the diameter of oxygen，nitrogen， air all become bigger; when both the release angle and dissolved air pressure isconstant， the diameter of oxygen is the biggest of all， and the diameter of nitrogen is theminimum. But the differences in diameter become small with the increase of dissolved airpressure.Through the above theoretical and experimental research， the factors which affect thediameter of micro air bubble in one-component dissolved air methods were analysed andargued. Make the theoretical basis and reference for using one-component dissolved airmethods to air flotation technology.