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Simulation of bubbly flow between parallel plates. Turbulent structures are shown in yellow and cyan; bubbles are shown in light gray.Image Credit: Igor Bolotnov
Multiphase Flows
https://ir.linkedin.com/in/moammad-jadidi-03ab8399
Dr. Mohammad Jadidi(Ph.D. in Mechanical Engineering)
Presented by: Mohammad Jadidi 2
For example, different-sized solid particles of the same material can be treated as different phases because each collection of particles with the same size will have a similar dynamical response to the flow field
In multiphase flow, a phase can be defined as an identifiable class of material that has a particular inertial response to and interaction with the flow and the potential field in which it is immersed.
Note:
What is Multiphase Flows?
Two or more distinct phases flowing simultaneously in mixture, and
Have some level of phase separation at a scale well above the molecular level
Multi-phase flows is simply any fluid flow system consisting of:
Multiphase Flows
Presented by: Mohammad Jadidi 3
Multiphase Flows
Multiphase flow regimes can be grouped into four categories:
1. Gas-Liquid or Liquid-Liquid Flows
2. Gas-Solid Flows
3. Liquid-Solid Flows
4. Three-Phase Flows
Classification of Multiphase Flows
Presented by: Mohammad Jadidi 4
Classification of Multiphase Flows: Gas-Liquid or Liquid-Liquid Flows
Bubbly flow: discrete gaseous or fluid bubbles in a continuous fluid. Droplet flow: discrete fluid droplets in a continuous gas. Slug flow: large bubbles in a continuous fluid. Stratified/free-surface flow: immiscible fluids separated by a clearly-defined
interface.
Bubbly flow Droplet flow Slug flow Stratified/free-surface flow
Multiphase Flows
Black color: liquid phase , White color: gas phase
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Classification of Multiphase Flows: Gas-Liquid Flows
Gas–liquid flows can, in principle, assume several different configurations.
Classification of gas–liquid flows (adapted from Ishii & Hibiki, 2006).
Dispersed Flows Mixed or transitional flows Separated flows
Multiphase Flows
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A generic two-phase vertical flow map
A very important factor is the diameter of the flow line, if the liquid and gas flow ratesare kept constant and the flow line size is decreased from 4” to 3”, both the superficial gasand liquid velocities will increase by a factor 16/9. Hence, in the two-phase flow map thispoint will move up and right along the diagonal to a new position. This could cause achange in flow regime, e.g. changing from bubbly flow to slug flow or changing fromslug flow to annular flow
Multiphase Flows
Multiphase Flow Regime Maps
Classification of Multiphase Flows: Gas-Liquid Flows
NOTE: See appendix for more examples of flow regime maps
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Classification of Multiphase Flows: Gas-Liquid Flows
Flow Regimes in Vertical Pipe Configuration
Multiphase Flows
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Multiphase Flows Classification of Multiphase Flows: Gas-Solid Flows
Particle-laden flow: This is flow of discrete particles in a continuous gas.
Pneumatic transport: This is a flow pattern that depends on factors such as solid loading, Reynolds numbers, and particle properties. Typical patterns are dune flow, slug flow, and homogeneous flow.
Fluidized bed: This consists of a vessel containing particles, into which a gas is introduced through a distributor. The gas rising through the bed suspends the particles. Depending on the gas flow rate, bubbles appear and rise through the bed, intensifying the mixing within the bed.
Particle Laden Flow through Industrial Cyclone
Gas–solid flow, identified as gas–solid or gas–droplet flows, is concerned with the motion of suspended solid or droplet in the gas phase
The following regimes are gas-solid flows
Presented by: Mohammad Jadidi 9
Multiphase Flows
Fluidization Regimes for Gas-Solid Suspension Flow
4 ton/hour fluidized bed incinerator for industrial wastes
Classification of Multiphase Flows: Gas-Solid Flows
Presented by: Mohammad Jadidi 10
Multiphase Flows Classification of Multiphase Flows: Gas-Solid Flows
Pneumatic transport: This is a flow pattern that depends on factors such as solid loading, Reynolds numbers, and particle properties. Typical patterns are dune flow, slug flow, and homogeneous flow.
Video: Low-Velocity, Dense-Phase Pneumatic Conveying System,by Mactenn, mactenn.com
Presented by: Mohammad Jadidi 11
Multiphase Flows Classification of Multiphase Flows: Gas-Solid Flows
Pneumatic transport: This is a flow pattern that depends on factors such as solid loading, Reynolds numbers, and particle properties. Typical patterns are dune flow, slug flow, and homogeneous flow.
VIDEO: semi dense phase pneumatic conveying of bulk material ((AZO Ltd.)
VIDEO: a simulation of a bulk material dilute phase pneumatic conveying (AZO Ltd.)
Presented by: Mohammad Jadidi 12
Multiphase Flows Classification of Multiphase Flows: Gas-Solid Flows
Pneumatic transport:
Dense Phase - Full Pipeline• Pressure is higher• Material velocity is lowest• Material nearly fully fills pipe line
Dense Phase - Slug Flowdense phase dune flowPressure is higherMaterial velocity remains quite low.Material forms moving dunes as it is conveyed.
Dense Phase - Bed FlowPressure is middling, lower than full dense phase. Material velocity is mixed. Bed material moves slow.Material above the moving bed is flowing above saltation velocity.
Lean Phase (Dilute Phase)Low pressure conveying Material moving at high velocity.All material is above saltation velocity, and is entrained in gas flow in pipe.Highest wearing conveying regime, also has high air consumption.
Presented by: Mohammad Jadidi 13
Multiphase Flows
Depending on the particle number density, Gas-Solid Flows can be characterized as either being dilute or dense
Classification of Multiphase Flows: Gas-Solid Flows
A dilute flow, is one in which the particle motion iscontrolled by the fluid forces (drag and lift)
A dense flow, on the other hand, is one in which the particle motion is controlled by collisions
Presented by: Mohammad Jadidi 14
Multiphase Flows Classification of Multiphase Flows: Liquid-Solid Flows
Liquid–solid flow is the transport of solid particles in liquid
The following regimes are liquid-solid flows
Slurry flow: This flow is the transport of particles in liquids.
Hydrotransport: This describes densely-distributed solid particles in a continuous liquid.
Sedimentation: This describes a tall column initially containing a uniform dispersed mixture of particles. At the bottom, the particles will slow down and form a sludge layer. At the top, a clear interface will appear, and in the middle a constant settling zone will exist.
Temporal evolution particle distribution during gravity-dominated sedimentation.
Image Credit: (Center for Turbulence Research , Annual Research Briefs 2003)
The Stokes number gives a measure of temporal correlation between particle velocity and the
fluid velocity and is defined as
𝑺𝒕 = 𝝉𝒑 / 𝝉𝑭 If St <<1, the particle response time is much
less than the characteristic time associated with the flow field. In this case the particles will have ample time to respond to changes in flow velocity and, the particle and fluid velocities will be nearly equal
If St>>1, then the particle will have essentially no time to respond to the fluid velocity changes and the particle velocity will be little affected by fluid velocity change
Presented by: Mohammad Jadidi 15
Multiphase Flows
Slurry flow: This flow is the transport of particles in liquids. In slurry flows, the Stokes number is normally less than 1.
VIDEO: Detailed large-eddy simulation of a turbulent slurry flow in a horizontal pipe with the formation of a static bed at the bottom. Performed using NGA by Jesse Capecelatro and Olivier Desjardins.
Classification of Multiphase Flows: Liquid-Solid Flows
Presented by: Mohammad Jadidi 16
Multiphase Flows
Hydrotransport: This describes densely-distributed solid particles in a continuous liquid.
Classification of Multiphase Flows: Liquid-Solid Flows
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Multiphase Flows
Three-phase flows are combinations of the other flow regimes listed in the previous sections.
Classification of Multiphase Flows: Three-phase flows
A trickle-bed reactor (TBR) is a chemical reactor that uses the downward
movement of a liquid and the downward (co-current) or upward (counter-current)
movement of gas over a packed bed of (catalyst) particles. It is considered to be
the simplest reactor type for performing catalytic reactions where a gas and
liquid (normally both reagents) are present in the reactor and accordingly it is
extensively used in processing plants. Typical examples are liquid-
phase hydrogenation, hydrodesulfurization, and hydrodenitrogenation inrefineries.
Presented by: Mohammad Jadidi 18
Appendix
Multiphase Flows
Presented by: Mohammad Jadidi 19
Multiphase Flows Examples of flow regime maps (Gas-Liquid Flows)
Flow regime map for the horizontal flow of an air/water mixture in a 5.1cm diameter pipe. Hatched regions are observed regime boundaries,
lines are theoretical predictions. Adapted from Weisman (1983).
Sketches of flow regimes for flow of air/water mixtures in ahorizontal, 5.1cm diameter pipe. Adapted from Weisman (1983).
Presented by: Mohammad Jadidi 20
Multiphase Flows Examples of flow regime maps (Vertical pipe flow)
Sketches of flow regimes for two-phase flow in a vertical pipe. Adapted from Weisman (1983).
A flow regime map for the flow of an air/water mixture in a vertical, 2.5cm diameter pipe showing the
experimentally observed transition regions hatched; adapted from Weisman (1983).
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Multiphase Flows
The evolution of the steam/water flow in a vertical boiler tube.
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It should be added that flow regime information such as that presented in previous slides appears to be valid both for flows that are not evolving with axial distance along the pipe and for flows, such as those in boiler tubes, in which the volume fraction is increasing with axial position.
Presented by: Mohammad Jadidi 22
Multiphase Flows Examples of flow regime maps (Slurry flow regimes)
When the particles are small so that their settling velocity is much less than the turbulent mixing velocities in the fluid and when the volume fraction of solids is low or moderate, the flow will be well-mixed. This is termed the homogeneous flow regime
Flow regimes for slurry flow in a horizontal pipeline.
NOTE: Typically homogeneous flow regime only occurs in practical slurry pipelines when all the particle sizes are of the order of tens of microns or less.
Presented by: Mohammad Jadidi 23
Multiphase Flows Examples of flow regime maps (Slurry flow regimes)
Flow regimes for slurry flow in a horizontal pipeline.
When particle sizes are larger than tens of microns, vertical gradients will occur in the concentration and the regime is termed heterogeneous
When a packed bed develops, the flow regime is known as a saltation flow. In a saltation flow, solid material may be transported in two ways, either because the bed moves or because material in suspension above the bed is carried along by the suspendingfluid.
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Multiphase Flows
Thanks
https://ir.linkedin.com/in/moammad-jadidi-03ab8399
Dr. Mohammad Jadidi(Ph.D. in Mechanical Engineering)
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