Lecture Objectives

- Finish Particle dynamics modeling - See some examples of particle tracking - Eulerian Modeling - Define deposition velocity

- Fluid Dynamics and CFD Review - Answer your questions

Eulerian Model

Approximate Method • Solve concentration equation (for particles)• Assumes that particle flow the stream line • Modified diffusion

Multiphase Model• Solve several sets of NS equations• Define the boundary conditions in-between phases• Mixture model• Secondary phase can be granular• Applicable for solid-fluid simulations

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

Boundary conditions for particlein the vicinity of surfaces

- ratio of the flux of particles at the considered surface and particle concentration per unit volume.

For Nd particles deposited on a surface at time t, the deposition velocity is :

Vde is the particle deposition velocity (m/s), Nd is the number of particles in air, is the number of particles in air, A is the area of the considered surface (m²),V is the volume of the room (m3).

Deposition velocity

Resuspension

Requires modeling based on empirical models or detail turbulence model (for example DNS) in boundary layer

NtA

VNv dde

Your questionsIf the momentum is steady state (in the large chamber), then my understanding is that "steady" should be selected in the Basic Parameters window. But since the (ozone) concentration decays over time, where in Airpak is that specified?

If you wanted to run a trainsient state simulation on say particle deposition or in my case concentration decay but you wanted to use a precalculated constant velocity gradient, how would that be done?

If the initial (ozone) concentration throughout the chamber is 140ppb, with a steady concentration of 10ppb coming into the chamber the entire time, then should the initial concentration for ozone in Basic Parameters be set to 140ppb? And if so, is the "fraction" dimension for the initial concentration a mole fraction?

What is the second equation that relates the Velocities?

This is a general question(s). Do you want to always use the mesh generator or are the times when you want to create your own mesh distribution? How do you create your own mesh distribution?

Your questions Can I get the concentration vs, the length along the duct? (NOT the post plane cut) I mean I would like to draw the concentration along the duct to see where is the highest and lowest points.

Is there a provision in Airpak to run different "runs" in order to do parametric analyses, as there is in E-quest?

When adding a new source/contaminant what is the required information needed to add it successfully to the library I have not done this to my model yet but when I tried I did not see emission rate as one of the tabs to add.

Could you go over the definition of a fan, and how we would create the curve empirically?

Your questionsI m having trouble assigning a different temperature inside the closet. Does the closet space or any enclosed area have to be assigned a temperature or will the model take care of the delta T when the ac is running.

In long duct (like what I have in the tunnel) how can I balance the pressure between the inside and outside of duct? (to avoid negative pressure inside the duct) I guess it has something to do with the distance between fans right?

In the space I am modeling, the supply air is a mixture of returned air from the space and fresh outside air.  Is there a way for me to set the species concentration as a function of the air leaving the space at the return vent?  If the concentration at the return is X ppm, and 0 ppm in the outside air, then the concentration of the mixed supply air will be (1-Y)*X ppm, where Y= the fraction of the supply air that is outside air. 

 How do you determine air flow velocity of different sized vents when you only know the total Volume flow rate?

Your questions

On my fan model, I have entered a manufacturer's flow rate for the fan properties.  After my flow calculations through the room, I find the actual flow is lower than my experimental values and other simulations.  Should I tweak the fan model by adjusting the flow rate until I get my expect flow rates in the structure, or tweak the pressure drop across the fan?

Sometimes Airpak crashes on me when I go over 2-3 million cells.  Is this my computer or a setting in Airpak?  Also, when the grid does run, there are very few iterations of the simulation.  Is this an error from my fault or does a finer grid require less iterations?