Lecture Objectives

1. Lecture Objectives • Learn about particle dynamics modeling • Discuss project and result accuracy evaluation

2. 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

3. Properties ASHRAE Transaction 2004

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

5. Human exposure ASHRAE Transaction 2004

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. Multiphase Flow Regimes Fluent user manual 2006

13. Challenging Problem:Application of CFD in a large space - The geometry should present correct geometry around large openings - The ratio between the total flow area and the floor area should be the same as in full scale - Air supply and return openings should be defined in a coarse grid sufficient for momentum and energy flow predictions The result will define global air and energy flow between zones but accuracy is insufficient for an analysis of the detail air velocity distribution in the zones. EXAMPLE: Five-Story Parking Garage Ventilation Multi-space building Course grid model properties www.airpak.fluent.com

14. Detail air velocity distribution in room Detail description of geometry Simple Description of Interior Furnishings can be described as A volume with additional pres- sure drop in the momentum Equations:

15. Engineering Application Unlimited number of problems! For example: http://www.ansys.com/products/airpak/solutions.asp?name=p1 http://www.cd-adapco.com/applications/building.html

16. - Simple geometry - Course mesh CO2 sources Occupied zone Human Exposure Airflow in the room vs. Airflow in vicinity of occupant CO2 distribution

17. Simulation of an occupant Detailed geometry: Good for local convection coefficient calculation at the skin Effect of breathing an movement decrease accuracy

18. Different level of geometry details • Avaraged geometry can be used for global effects • Simple geometry can be used for semi-global effects • Detailed geometry should be used for local effects • Conclusions from geometry analysis (Peter Nielsen) • Semi-global effect • Differences in geometry have a small influence on • velocity, temperature distribution, contaminant distribution • far from the manikin • Local effect • Differences in geometry have an effect on velocity and • concentration distribution close to a person and exposure of • a person

19. We Often Need Experimental Validation Room with nonuniform temporal and spatial distribution of particles (for example smoke) Validation results for 0.74 m S1 CFD model Monitoring Position S1 Monitoring Position S2 S2 Pollution Source active 2 minutes Experiment

20. Examples of CFD application in Indoor environment research Some hot topics • Particle Transport in a boundary layer • Surface Chemistry • Air and particle flow in lung • Various analyses of fluid flow in building components and HVAC systems