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

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

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

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

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

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

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?

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

Thermal comfort Temperature and relative humidity

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

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

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 ( -0.036 M ) + 0.028 ] 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 = 100 - 95 exp [ - (0.03353 PMV4 + 0.2179 PMV2)] Empirical correlations Ole Fanger Further Details: ANSI/ASHRAE standard 55, ISO standard 7730

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

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

Multiphase Flow Regimes Fluent user manual 2006

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