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Lecture Objectives

Lecture Objectives. Analyze some examples related to natural ventilation Introduce particle dynamics modeling . External flow. Wind profile. Buoyancy driven indoor flow. Important parameters Geometry Heat sources Intensity (defined temperature or heat flux) Distribution

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Lecture Objectives

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  1. Lecture Objectives • Analyze some examples related to natural ventilation • Introduce particle dynamics modeling

  2. External flow Wind profile

  3. Buoyancy driven indoor flow Important parameters • Geometry • Heat sources • Intensity (defined temperature or heat flux) • Distribution • Change (for unsteady-state problem) • Openings Defined • Pressure • Velocity

  4. Natural Ventilation:Stack-driven flow in an atrium

  5. Natural Ventilation:Wind scoop

  6. Natural Ventilation:Solar-assisted ventilation

  7. Window Design

  8. Natural Ventilation:

  9. Natural Ventilation:

  10. Example of natural ventilation

  11. Energy Simulation Program Air Flow Program Coupling Twall,CFM, Tsupply Data: geometry weather materials IAQ V,T,… Energy cons. Tnear surface, h surface

  12. COUPLING METHODS One-directional coupling (Quasi steady state CFD simulation)

  13. Coupling

  14. COUPLED PROGRAM Components and Data flow

  15. Particulate matters (PM) • Properties • Size, density, liquid, solid, combination, … • Sources • Airborne, infiltration, resuspension, ventilation,… • Sinks • Deposition, filtration, ventilation (dilution),… • Distribution - Uniform and nonuniform • Human exposure

  16. Properties ASHRAE Transaction 2004

  17. Particle size distribution ASHRAE Transaction 2004 Ventilation system affect the PM concentration in indoor environment !

  18. Human exposure ASHRAE Transaction 2004

  19. Two basic approaches for modeling of particle dynamics • Lagrangian Model • particle tracking • For each particle ma=SF • Eulerian Model • Multiphase flow (fluid and particles) • Set of two systems of equations

  20. m∙a=SF Lagrangian Modelparticle tracking A trajectory of the particle in the vicinity of the spherical collector is governed by the Newton’s equation Forces that affect the particle • (rVvolume) particle∙dvx/dt=SFx • (rVvolume) particle∙dvy/dt=SFy • (rVvolume) particle∙dvz/dt=SFz System of equation for each particle Solution is velocity and direction of each particle

  21. Lagrangian Modelparticle tracking Basic equations - momentum equation based on Newton's second law Drag force due to the friction between particle and air - dp is the particle's diameter, - p is the particle density, - up and u are the particle and fluid instantaneous velocities in the i direction, - Fe represents the external forces (for example gravity force). This equation is solved at each time step for every particle. The particle position xi of each particle are obtained using the following equation: For finite time step

  22. Algorithm for CFD and particle tracking Unsteady state airflow Steady state airflow Airflow (u,v,w) for time step  Airflow (u,v,w) Steady state Injection of particles Injection of particles Particle distribution for time step  Particle distribution for time step  Airflow (u,v,w) for time step + Particle distribution for time step + Particle distribution for time step + Particle distribution for time step +2 ….. ….. One way coupling Case 1 when airflow is not affected by particle flow Case 2 particle dynamics affects the airflow Two way coupling

  23. Eulerian Model • Solve several sets of NS equations • Define the boundary conditions in-between phases Multiphase/Mixture Model • Mixture model • Secondary phase can be granular • Applicable for solid-fluid simulations • Granular physics • Solve total granular pressure to momentum equation • Use Solids viscosity for dispersed solid phase • Density difference should be small. • Useful mainly for liquid-solids multiphase systems There are models applicable for particles in the air

  24. Multiphase flow Multiphase flow can be classified in the following regimes: • gas-liquid or liquid-liquid flows • gas-solid flows • particle-laden flow: discrete solid particles in a continuous gas • pneumatic transport: flow pattern depends on factors such as solid loading, Reynolds numbers, and particle properties. Typical patterns are dune flow, slug flow, packed beds, and homogeneous flow. • fluidized beds: consist of a vertical cylinder containing particles where gas is introduced through a distributor. • liquid-solid flows • three-phase flows

  25. Multiphase Flow Regimes Fluent user manual 2006

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