00 multiphase flows - intorduction

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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

    Jadidi.cfd@gmail.com

    Dr. Mohammad Jadidi(Ph.D. in Mechanical Engineering)

    mailto:Jadidi.cfd@gmail.com

  • 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

  • Presented by: Mohammad Jadidi 5

    Classification of Multiphase Flows: Gas-Liquid Flows

    Gasliquid flows can, in principle, assume several different configurations.

    Classification of gasliquid flows (adapted from Ishii & Hibiki, 2006).

    Dispersed Flows Mixed or transitional flows Separated flows

    Multiphase Flows

  • Presented by: Mohammad Jadidi 6

    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

  • Presented by: Mohammad Jadidi 7

    Classification of Multiphase Flows: Gas-Liquid Flows

    Flow Regimes in Vertical Pipe Configuration

    Multiphase Flows

  • Presented by: Mohammad Jadidi 8

    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

    Gassolid flow, identified as gassolid or gasdroplet 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

    Liquidsolid 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

    = / 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

  • Presented by: Mohammad Jadidi 17

    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.

    https://en.wikipedia.org/wiki/Chemical_reactorhttps://en.wikipedia.org/wiki/Catalysthttps://en.wikipedia.org/wiki/Hydrogenationhttps://en.wikipedia.org/wiki/Hydrodesulfurizationhttps://en.wikipedia.org/wiki/Hydrodenitrogenation

  • 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