1 / 23

# Lecture Objectives - PowerPoint PPT Presentation

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?

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

## PowerPoint Slideshow about ' Lecture Objectives' - pearl-wilkinson

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

• Finish with age of air modeling

• Introduce particle dynamics modeling

• Analyze some examples related to natural ventilation

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)

• 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?

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

• Properties

• Size, density, liquid, solid, combination, …

• Sources

• Airborne, infiltration, resuspension, ventilation,…

• Sinks

• Deposition, filtration, ventilation (dilution),…

• Distribution

- Uniform and nonuniform

• Human exposure

ASHRAE

Transaction 2004

ASHRAE Transaction 2004

Ventilation system affect the PM concentration in indoor environment !

ASHRAE Transaction 2004

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

• 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

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

Algorithm for CFD and particle tracking

Airflow (u,v,w) for time step 

Airflow (u,v,w)

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

Natural Ventilation:Science Park, Gelsenkirchen, Germany

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)

Wind profile

Important parameters

• Geometry

• Heat sources

• Intensity (defined temperature or heat flux)

• Distribution

• Change (for unsteady-state problem)

• Openings

Defined

• Pressure

• Velocity

Natural Ventilation:Stack-driven flow in an atrium

Natural Ventilation:Solar-assisted ventilation