Learning Forum

[Lylad]

Hi I am creating a simulation with a cow releasing infectious aerosol, I can created my flow and while running my particle results I have been using the colour by discrete phase variables and DPM concentration. But I am just a bit confused about the units it says the units are kg/m^3, so I am just a bit confused what this meaning in terms of concentration and how it can be interpreted.

Also when trying to change the units I noticed the default for DPM concentration says 1.e15-particles/ kg, I am also confused what this means?

Thank you :)

[Rob]

There aren't alternative units for DPM Concentration, but there are for concentration. I think the particle-conc is something else, especially as it's per kg, lb or g but the 1e15 remains constant.

[Lylad]

Hi rob thank you so much for your reply, I just wanted to ask another question, when your creating the injections one of the options for point properties is the Flow rate (kg/s) for the particles, the default value is 1e-20, but is this something you need to calculate beforehand ?
If so is there a formula to calculate the flow rate ?

[Rob]

You need to give the solver a flow rate if using two way coupling. The 1e-20 kg/s is for one way as the solver needs a mass for something. Historically if we were just tracking particles one way (flow affects the trajectory but trajectory doesn't alter the flow) we set a mass of 0 kg/s.
Flow rate is how much mass you want in the system. We use a parcel method so you're tracking the parcel not the particle: not helped that everyone always muddles the two terms.

[Lylad]

Hi rob thank you for your reply, I am using a one- way simulation so that fine but would it be best to leave the flow rate at 1e-20 or change it to 0 as you said.

[Rob]

Don't change to zero. You won't get any particles if you do that! So leave the mass flow as 1e-20.

[Lylad]

Thank you so much :)

[Rob]

You're welcome.