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Book Chapter
Research Papers in Conferences
Study the hydrodynamics such as rheology, pressure drop and friction factor of the suspension flow of microbubbles. In the present study, experiments were conducted to study the hydrodynamics and mineral enrichment efficiency of microbubble suspension flow.
BACKGROUND AND FORMULATION OF WORK 1-30
Different Aspects of Microbubble Flotation for Fine Separation 16
GENERATION OF MICROBUBBLE AND ITS STABILITY 31-53
FLOW CHARACTERISTICS OF MICROBUBBLE 77-106
DISPERSION CHARACTERISTICS OF MICROBUBBLE SUSPENSION IN CONTINUOUS PLANT PROTOTYPE
MINERAL BENEFICIATION BY IONIC MICROBUBBLE 139-177
OVERALL CONCLUSIONS AND RECOMMENDATIONS 179-182
BACKGROUND AND FORMULATION OF WORK
Background of the Study
- Characteristics of Microbubbles
- Definition
- Components of Microbubble
- Properties of Microbubble
- Zeta potential
- Rheological behaviour
Important characteristics of the zeta potential of microbubbles are as follows: i) Addition of electrolytes such as NaCl and MgCl2 causes the negative zeta potential to decrease to a less negative value (Lyklema, 2000). ii) The zeta potential of the microbubbles in the solution is affected by the addition of alcohol (methanol, 2-propanol and butanol) to the solution. A suspension of microbubbles exhibits non-Newtonian behavior (Shams et al., 2014). The viscosity of microbubbles generally decreases with increasing shear stress (Shen et al., 2008).
Applications of Microbubbles
- Mass Transfer Enhancement
- Water Purification
- Drag Reduction
- Oil Separation
- Fine Particle Separation
It has been reported that the decolorization reaction constant in the microbubble system is 2.1 times higher than the conventional bubble system (Tasaki et al., 2009). They reported that oil separation from highly concentrated oil-in-water emulsion was significantly improved by microbubble injection and approximately 70-80% of the oil could be removed by microbubble flotation. Deng et al. 2011) developed a T-tube dynamic state flotation device.
Different Aspects of Microbubble Flotation for Fine Separation
- Engineering Aspects
- Dispersion Characteristics of Microbubble
- Design of Unit
- Microbubble Generation
- Physical Aspects of Ionic Microbubble Flotation
- Particle Hydrophobicity and Floatability
- Bubble–Particle Interactions
- Microbubble Stability
- Hydrodynamics of Microbubble Flow
- Chemical Aspects of Microbubble Flotation
- Surface Chemistry of Minerals in Water
- Chemistry of Flotation Reagents
The hydrodynamic forces are due to the resistance of liquid films between the surfaces (Dai et al., 1999). Although the actual double layer interactions between the particle and microbubble occur in limited distance (Fuerstenau et al., 2007;Nguyen, 2007).
Knowledge Gap
The size of the microbubble surface charge is governed by the surfactant concentration (Yoon and Yordan, 1986). In order to achieve the technical feasibility of microbubble suspension flow and microbubble-assisted mineral separation by flotation, a detailed study on the dispersion characteristics of the microbubble suspension is also required.
Formulation of the Work
- Microbubble Generation and Stability of Microbubble
- Rise Velocity and Size Distribution of Microbubble
- Hydrodynamics of Microbubble Flow
- Dispersion Characteristic of Ionic Microbubble
- Fine Particle Separation by Ionic Microbubble
The present work investigates the hydrodynamic characteristics of the flow of a suspension of microbubbles in a surfactant solution through a tube. General correlations for the flotation rate constant and induction time are also developed based on the physicochemical properties of the microbubble particle mixture. Details are provided in Chapter 6.
Notations
The effects of various operating variables and physicochemical properties of liquid on the separation characteristics of ionic microbubbles are enunciated. An analysis of particle recovery based on microbubble dispersion mixing phenomena is also presented.
Greek letters
A phenomenological kinetic model based on the collision, adhesion and detachment mechanisms of fine particles is developed to analyze the flotation characteristics of ionic microbubbles.
GENERATION OF MICROBUBBLE AND ITS STABILITY
Introduction
The stability of microbubbles is another aspect that is highly focused on their practical application. From the literature review above, it is clear that the stability of microbubbles can be improved by using a surfactant.
Experimental Procedure
- Microbubble Generation by Pressurized Dissolution Method
- Stability Measurement by the Drainage Curve Method
- Stability Measurement by the Electrical Conductivity Method
Freshly prepared microbubbles were transferred to the measuring cylinder and the volume of the drained liquid under the dispersion was measured over time, as shown in the schematic diagram in Figure 2.3. According to Sebba (1985), the stability of the microbubble dispersion was quantified as the time required for half of the liquid to drain from the dispersion, i.e. the half-life (T1/2). For integral measurements, the position of the probe was fixed at the bottom of the cylinder and the EC values were recorded against time.
Physical Properties of the System
Results and Discussion
- Kinetics of Stability of Microbubble
- Modeling for Liquid Drainage
- Stability based on Electrical Conductivity
- Modeling for Electrical Conductivity
The values of q in the model were found to depend mainly on the surfactant concentration. The drainage mechanism in the first stage is a combination of fluid flow due to gravity through the plateau boundary and upward creaming of microbubbles. In this phase, the drainage rate is much less due to a small fraction of microbubbles remaining in the dispersion.
Conclusion
TERMINAL RISE VELOCITY AND SIZE DISTRIBUTION OF MICROBUBBLE
Introduction
The rate of rise of microbubbles showed perfect agreement with the theoretical correlation, but as the bubble size increased, the discrepancy also increased (Duineveld, 1995). Takahashi (2005) reported that the rising speed of the swarm of microbubbles in distilled water was close to the value calculated from Stokes' law. In this chapter, the hydrodynamic parameters such as bubble size distribution and rise rate of microbubbles in different liquids are reported.
Theoretical Background
- Terminal rise velocity
Fan and Tsuchiya (1990) developed a correlation to determine the final bubble rise rate applicable to a clean and contaminated system. Thus, the final rise rate of microbubbles (Ub) can be described by Stokes' law (Takahashi, 2005). Stokes (Stokes, 1851) expressed the final speed of the rise of a bubble in a viscous liquid at a low Reynolds number as
Experimental Procedure
- Estimation of Bubble Size Distribution and Rise Velocity
Bubble size was estimated using the same software and a total of 300-400 bubbles were examined to determine the size. The rising trajectories of the microbubbles were recorded with a high-resolution camera (Sony DSC-HX10V). Assuming no microbubble aggregation and breakup, the diameter of microbubbles rising in a standing liquid can be calculated by
Physical Properties of the System
The microbubble rise rate can be easily calculated from the distance moved by the microbubble swarm between two scale marks and the time interval between these marks according to Eq.
Results and Discussion
- Effect of Physicochemical Properties of Liquid on Size Distribution of Microbubble
- Effect of Addition of SCMC on Rise Velocity of Microbubble
- Effect of Addition of Surfactants on Rise Velocity of Microbubble
- Effect of addition of Glycerol on Terminal Velocity of Microbubble
The effects of SCMC concentration on the terminal rise velocity of microbubbles with different gases are shown in Figure 3.9. It is observed that the microbubble rise rate for all gases decreases with increasing SCMC concentration. The rate of rise is a function of gas density, liquid viscosity and bubble size (according to Stokes' law).
Conclusion
FLOW CHARACTERISTICS OF MICROBUBBLE
Introduction
Flow laminarization can occur even at a low gas retention of 0.2% (Serizawa et al., 2003). However, no qualitative information is available in the literature to relate gas retention in microbubbles to surfactant concentration (Aslan et al., 2006). Drag reduction with microbubble suspension was found to be affected by gas retention and pipe curvature (Shatat et al., 2009;.
Theoretical Background
- Properties of Microbubble Suspension Flow
- Analysis of Interfacial Shear Stress in Microbubble Suspension Flow
The energy loss due to liquid wetting depends on the dynamic contact angle between the liquid and solid wall. To determine the friction losses due to fluid flow in the pipe, a model can be formulated based on the following assumptions: i). The value of l is equal to the specific interface area in the test pipe section.
Experimental Setup and Procedure
- Estimation of Pressure Drop
- Estimation of Gas Holdup
- Physical Properties of the System
Gas holdup is defined as the volume fraction of the gas phase occupied by bubbles. Alternating current (ac) with sufficiently high frequency (about 1000 Hz) and low voltage (∼1.5 V) was used to avoid polarization of the electrodes. The effective viscosity of the fluid flowing through the tube was calculated according to Eq.
Results and Discussion
- Variation of Gas Holdup
- Shear Stress in Microbubble Suspension Flow
- Wall Friction Factor
- Friction Factor in Microbubble Suspension Flow based on Energy Loss due to Wettability
- Hydrodynamic Drag Coefficient in Microbubble Suspension Flow
The non-Newtonian nature of microbubble suspensions was found to depend on the concentration of surfactants in the suspension. The extent of non-Newtonian behavior, however, depends primarily on the physicochemical properties of the fluid. The variation of the friction factor with energy losses due to wettability on different surfaces is shown in figure 4.10.
Conclusion
The developed correlation within the sets of variables was found to be in good agreement with each other. The friction factor was found to decrease inversely proportional to the Reynolds number up to the power of 0.45, while without the microbubble suspension it decreased to the power of 0.25. The drag coefficient was found to decrease with increasing Reynolds number, as well as with increasing concentration of surfactants in the suspension.
DISPERSION CHARACTERISTICS OF
MICROBUBBLE SUSPENSION IN CONTINUOUS PLANT PROTOTYPE
Introduction
Although mass transfer properties and hydrodynamic properties of microbubbles have been discussed in the literature, there is still a considerable gap in knowledge about the dispersion mechanism of microbubble suspension flow. In order to achieve the technical feasibility of microbubble suspension flow and microbubble-assisted mineral separation by flotation, a detailed study on the dispersion characteristics of microbubble suspension is required. Thus, in this chapter we tried to investigate the dispersion characteristic and the mixing time of the microbubble suspension of the recirculation system in a prototype continuous plant, which has not been reported to date.
Theoretical Background
- Dispersion Coefficient of Microbubble Suspension
- Mixing Time of Microbubble Suspension
In the circulation region, the dispersion follows a different pattern than the continuous non-circulation region. The dispersion of the tracer in the circulation area is mainly caused by the differences in the speed of the different flow lines and the differences in the length of the different circulation loops inside the device. The spread of the circulating current seems to be conceivable from the average circulation time and a coefficient which characterizes the spread during the circulation.
Experimental Setup and Procedure
- Experimental Setup
- Calibration of Conductivity Meter
- Effective Viscosity of Microbubble Suspension
- Estimation of Mixing Time
- Estimation of Dispersion Coefficient
In the present study, the mixing characteristics of the microbubble suspension are evaluated by the tracking technique. In the present work, the mixing time is marked when the tracer concentration reaches 98%. In this work, the value of the dispersion coefficient was calculated from the Bodenstein number (according to Eq.
Results and Discussion
- Effect of Phase Velocities on Dispersion Coefficient
- Effect of Suspension Properties on Dispersion Coefficient
- Effect of Circulation Velocity of Suspension on Mixing Time
- Effect of Microbubble Suspension Properties on Mixing Time
- Model Development to Interpret the Intensity of Dispersion
- Interpretation on Dispersion due to Suspension Circulation
It was found that the dispersion coefficient due to fluid circulation increases with increasing suspension circulation rate. The circulation rate of the liquid in the column is increased by increasing the circulation rate of the microbubble suspension. The effect of SCMC on the dispersion coefficient due to fluid circulation is shown in Figure 5.17.
Conclusion
A high fluid exchange will not contribute to a high dispersion unless there is sufficient turbulence and circulation in the system. The dispersion coefficient due to fluid circulation of the slurry is dependent on the phase velocity, surfactant concentrations and SCMC concentration in the slurry. The distribution coefficient due to fluid circulation of the suspension increased with increasing suspension circulation velocity.
MINERAL BENEFICIATION BY IONIC MICROBUBBLE
Introduction
To recover fine mineral particles, the flotation cell must have fine bubbles or microbubbles suitable for capturing these particles (Trahar and Warren, 1976). Microbubble-assisted flotation is widely applied in various fields for process intensification. They concluded that electrostatic interactions were the driving force behind the separation. 2008) also used ionic microbubbles to separate a fine binary mixture of minerals.
Experimental Setup and Procedure .1 Materials
- Experimental Setup
- Determination of ZnO
- Determination of Al 2 O 3 and CuO
- Estimation of Zeta Potential of Particle
- Estimation of Particle and Microbubble Size
Both the inlet and outlet of the column were located at the lower end, through which the microbubble generator was connected. The circulation rate in the flotation column is determined by Qm/(Ac/2), where Qm is the volumetric flow rate of the microbubble particle mixture, measured by a rotameter, and Ac is the cross-sectional area of the flotation column. The zeta potential of particles in a surfactant solution (surfactant and water) was measured using a zeta potentiometer (Model-Delsa Nano C, Beckman Coulter, Nyon, Switzerland) based on the electrophoretic mobility of the particle (Tantra et al., 2010; Waters, 2008).
Results and Discussion
- Effect of Mixture Velocity on Recovery of Mineral Particles
- Effects of Surfactants on Flotation Recovery of ZnO
- Effects of Surfactants on Flotation Recovery of CuO
- Effects of Surfactants on Al 2 O 3 Recovery
- Variation of Recovery of Particle with Time
- Model for Microbubble Flotation
- Collision Efficiency
- Stability Efficiency
- Attachment Efficiency
- Interpretation on Induction Time
- Interpretation on Flotation Rate Constant
After collision with the rising microbubble, the particle attaches to the surface of the bubble and forms a stable particle-bubble aggregate. The effects of adding different surfactants on CuO recovery are shown in Figure 6.6. Increasing the mixing speed decreases the adhesion time of bubbles and particles, which leads to a decrease in the induction time. 1989) also reported a dependence of the induction on the velocity of the bubble approaching the particle.
