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Lecture Objectives

This lecture discusses the effectiveness of ventilation, thermal comfort, and other CFD results representation in the context of surface radiation models and particle modeling. It explores various indicators such as age-of-air, specific contaminant concentration, and air-change efficiency to assess the quality of air in a space. Additionally, it examines the prediction of thermal comfort using parameters like temperature, relative humidity, and velocity. The lecture also explains the modeling of multiphase flow and particle dynamics in CFD simulations.

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Lecture Objectives

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Presentation Transcript

  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 qualitative indicator 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 valueIAQ indicatorsEv 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. 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)

  6. Air exchange efficiency for characteristic room ventilation flow types

  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. 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

  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 ( -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

  13. Surface Radiation ModelsCombined 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 • Lagrangian Model • particle tracking • For each particle ma=SF • Eulerian Model • Multiphase flow (fluid and particles) • Set of two systems of equations

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