topic Re: Multiple Boundary Conditions on one surface in CFD Forum

Multiple Boundary Conditions on one surface

Anonymous — Mon, 15 Jun 2015 09:42:43 GMT

I have a query regarding inputting multiple boundary conditions onto a single surface.

In this hypothetical situation I have 2 rooms, separated by a glass door. One room is hot (say 40°C) and the other room is cool (20°C).

There is an infiltration rate through the door from the hot room to the cold room, for which I have detailed second-by-second data for.

Is there any issue in specifying 3 boundary conditions onto the glass door surface as follows:

Piecewise linear air flow for the infiltration m3/s
Steady state temperature of 40°C for the infiltration
Total Heat Flux of xW for the conduction gain from the glass door surface into the cold room.

Any advice is greatly appreciated.

Kind regards,

Re: Multiple Boundary Conditions on one surface

Jon.Wilde — Mon, 15 Jun 2015 13:42:00 GMT

Hi,

Bearing in mind you cannot model internal conitions, this should be fine. Just don't model the warmer room and use BC's to match the effect it is having.

The leakage path (air inlet) can have a flow and temp assigned and yes, it is also OK to have a heat flux on the glass surface.

Does that help?

Kind regards,

Jon

Re: Multiple Boundary Conditions on one surface

Anonymous — Fri, 19 Jun 2015 03:43:45 GMT

Thanks Jon,
Just to be clear the leakage is specified over the whole door surface rather than around the edges of the door. So on one surface I have the 3 boundary conditions?

Re: Multiple Boundary Conditions on one surface

Jon.Wilde — Mon, 22 Jun 2015 08:37:19 GMT

Hi,

Are all of these conditions on an inlet surface though? Not embedded within the model?

Re: Multiple Boundary Conditions on one surface

Anonymous — Tue, 23 Jun 2015 03:11:28 GMT

Jon,

Not entirely sure what you mean by this. Could you differentiate further?

Also, I have another query related to this. Given the heat gain from conduction into the 'cold' room is driven by the temperature difference between the 2 rooms, is there a way to model a fluctuating heat flux?

For example over the length of a simulation the conduction gain reduced as the temperature differential is reduced?

Kind regards,

Andrew

Re: Multiple Boundary Conditions on one surface

Jon.Wilde — Tue, 23 Jun 2015 08:39:09 GMT

What I meant is that you cannot have flow or temerature boundary conditions on anything other than the model boundary - so a real inlet or outlet. Nothing internally.

You could have a part that was assigned a volumetric heat load internally, so the air could heat up as it passed by. This could be set to vary over time - stick with steady state to start with and get that running well first though.