1. Lecture Objectives Discuss HW4
Ventilation Effectiveness, Thermal Comfort, and other CFD results representation
Surface Radiation Models
Particle modeling

2. Air and Species Dispersion parameters
Number of ACH
quantitative indicator
ACH - for total air
- for fresh air
Ventilation effectiveness
qualitative indicator
takes into account air distribution in the space
Exposure
takes into account air distribution and source position and intensity

3. Indices Age-of-air air-change effectiveness (EV)
Specific Contaminant Concentration
contaminant removal effectiveness e

4. Single value IAQ indicators Ev and ε
Contaminant removal effectiveness (e)
concentration at exhaust
average contaminant concentration
Contamination level
2. Air-change efficiency (Ev)
shortest time for replacing the air
average of local values of age of air
Air freshness

5. Air-change efficiency (Ev)
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

6. Air exchange efficiency for characteristic room ventilation flow types
Flow pattern
Air-change
efficiency
Comparison with average time of exchange
Unidirectional flow
1 - 2
tn < texc < 2tn
Perfect mixing 1
texc = tn
Short Circuiting
0 - 1
texc > tn

7. 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?

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

9. Thermal comfort
Temperature and relative humidity

10. Thermal comfort Velocity Can create draft
Draft is related to air temperature,
air velocity, and turbulence intensity.

11. Thermal comfort Mean radiant temperature potential problems Asymmetry
Warm ceiling (----)
Cool wall (---)
Cool ceiling (--)
Warm wall (-)

12. Prediction of thermal comfort
Predicted Mean Vote (PMV)
+ 3 hot
+ 2 warm
+ 1 slightly warm
PMV = 0 neutral
-1 slightly cool
-2 cool
-3 cold
PMV = [0.303 exp ( M ) ] L
L - Thermal load on the body
L = Internal heat production – heat loss to the actual environment
L = M - W - [( Csk + Rsk + Esk ) + ( Cres + Eres )]
Predicted Percentage Dissatisfied (PPD)
PPD = exp [ - ( PMV PMV2)]
Empirical correlations
Ole Fanger
Further Details: ANSI/ASHRAE standard 55, ISO standard 7730

13. Surface Radiation Models Combined with CFD
Example:
Heat transfer through
a window
Cavity:
CFD
Domain

14. 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

15. Multiphase Flow Regimes
Fluent user manual 2006

16. Two basic approaches for modeling of particle dynamics
PM Modeling
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