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Lecture Objectives

Lecture Objectives. Finish with age of air modeling Introduce particle dynamics modeling Analyze some examples related to natural ventilation. Depends only on airflow pattern in a room We need to calculate age of air ( t ) Average time of exchange What is the age of air at the exhaust?

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Lecture Objectives

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  1. Lecture Objectives • Finish with age of air modeling • Introduce particle dynamics modeling • Analyze some examples related to natural ventilation

  2. Depends only on airflow pattern in a room We need to calculate age of air (t) Average time of exchange What is the age of air at the exhaust? Type of flow Perfect mixing Piston (unidirectional) flow Flow with stagnation and short-circuiting flow Air-change efficiency (Ev)

  3. Contaminant removal effectiveness (e) • Depends on: • position of a contaminant source • Airflow in the room • Questions 1) Is the concentration of pollutant in the room with stratified flow larger or smaller that the concentration with perfect mixing? 2) How to find the concentration at exhaust of the room?

  4. Ev= 0.41 e= 0.19 e= 2.20 Differences and similarities of Evande Depending on the source position: - similar or - completely different air quality

  5. 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

  6. Properties ASHRAE Transaction 2004

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

  8. Human exposure ASHRAE Transaction 2004

  9. 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

  10. 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

  11. 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

  12. 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

  13. Natural Ventilation:Science Park, Gelsenkirchen, Germany

  14. Natural Ventilation and CFD simulation • Wind driven outdoor flow • Buoyancy driven indoor flow Solution approach • Model boundary condition in-between outdoor and indoor domain • Couple CFD with • 1) energy simulation program (buoyancy driven flow) • 2) multi-zone modeling program (inter-zonal flow)

  15. External flow Wind profile

  16. 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

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

  18. Natural Ventilation:Wind scoop

  19. Natural Ventilation:Solar-assisted ventilation

  20. Window Design

  21. Natural Ventilation:

  22. Natural Ventilation:

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