Experimental Study Of Surfactant Effect On Motion Characteristic Of Single Bubble

The cyclonic-static micro-bubble flotation column is widely used in coal preparation and mineral separation for its better separation selectivity and suitability of fine particles separation. In flotation process, gas is normally introduced into a flotation column in the form of small bubbles and acts as carriers transporting particles to the surface of the continuous liquid phase. Bubble size and movement law will affect the ability of carrying particles directly. Surfactants are generally used to control bubble size and stability. Therefore, it is significantly essential to research bubble dynamic characteristics in the presence of surfactants, and set up the relation of surfactants concentration and bubble movement, provide theoretical basis for improvement of the efficiency of the flotation process.DL-2-Octanol which is generally used as surfactants in flotation process is chosen as the research object in this thesis. Kruss K100 surface tension meter is used to test the surface tension of DL-2-Octanol solution with different concentration. Then OLYMPUS i-SPEED3 high speed dynamic system is used to record the movement of single bubble in surfactants condition. At last, the i-SPEED Suite software and Image-Pro Plus7.0 software were used for the analysis of bubble size, shape, trajectory, coordinate and rising velocity. Base on a large amount of experimental datas, the effect of surfactants on bubble size, shape, trajectory, rising velocity and drag coefficient is obtained.Experimental results show that the presence of surfactants can reduce bubble size, retard bubble deformation, enhance the stability of bubble movement, and reduce bubble velocity. Because of the presence of surfactants, bubble velocity increases to maximal velocity after divorce from nozzle, then decreases to a terminal velocity, and surfactants can reduce the velocity difference of maximal velocity and terminal velocity. Large bubble deformation coefficient results in large velocity and bubble close to spherical has small velocity. The increase of surfactants concentration results in the decrease of fluctuation cycle of instantaneous velocity.In this experiment, bubbles are not exactly ellipsoid, the bubble deformation is characterized with bubble area and perimeter without shape assumption, and deformation coefficient is expressed in the form of surface tension, Eo, Re and We. And the biggest average relative error of deformation coefficient from experiment and modified equation is 2.07%. Base on Mendelson velocity equation, a new velocity model is set up for surfactants condition, and the biggest average relative error of velocity from experiment and corrected equation is 3.47%. Base on Schiller-Nauman drag model, a new drag model is set up for surfactants condition, and the biggest average relative error of drag coefficient from experiment and corrected equation is 4.16%. Above corrected models can be used for the CFD calculation of flotation process.