# SLA Printer HVAC

I bought an SLA printer, I tried to print and noticed that the smell was getting too strong, so I came back tosimscale and tried to find a solution. First the SLA printer has an embedded HVAC system that has a flow rate of 0.001106 m^2/s. Then I searched the nearby stores what they were selling, I found a Exauster that has the flow rate of 0.0194 m^2/s.
I proceeded to create different versions of a possible CAD model, the final (and I hope the correct one) is called Printer_clear v.3.3.

In this image the exhaust and HVAC from the SLA printer are highlighted, the top one is the Exauster and the bottom is the Printer HVAC.

I have had a successful simulation with this geometry, but it had a simple and basic mesh, just to try, so the time steps were only 2 and the graphic quality is bad, as it can be seen in the following image. (simulation 9)

Almost all of the simulations after this one give the error as follows.
â€śThe solution diverged, most likely due to presence of bad elements in the mesh. Such elements tend to exist near walls and sharp corners. Visually inspect your mesh to locate them and re-mesh with additional refinements in their vicinity. If you are confident about the mesh-quality, please reduce relaxation factors and use more conservative numerical schemes.â€ť

Furthermore i serched the mesh logs and found this: â€śChecking faces in error :
non-orthogonality > 70 degrees : 0
faces with face pyramid volume < 1e-20 : 0
faces with concavity > 80 degrees : 0
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0â€¦1) < 0.02 : 0
faces with volume ratio of neighbour cells < 0.01 : 0
faces with face twist < 0.01 : 0
faces on cells with determinant < 0.001 : 0
Finished meshing without any errors
Finished meshing in = 389.28 s.
Endâ€ť.

Note : the CAD is highly simplified, therefore sorry if the scaling is a bit off.

The project link is here: https://www.simscale.com/projects/pgalamba/printer_evac/

To end this post i will say, thank you for you time and patience to help me.

The image â€śSuccessPrintFLowâ€ť the yellow is the Exaust and orange is the printer.

My guess is that there is a thin amount of space beetween the bottom and the printer, as follows:

As indicated by the brown collor.

Hi @pgalamba and thanks for the detailed description of your problem!

I am quite sure that the mesh can be used for a first rough estimate and you have no illegal cells or problems with sharp corners as far as I can tell at the moment. Could you explain why you have the top inlet and outlet surfaces explicitly defined as additional boundary conditions (BCs)? I assume that these both cause the simulation to diverge due to a violation of the conservation of mass.

Unfortunately you deleted the successful runs so could have had a look at the results and see if the output quantities make sense. Tagging the @cfd_squad in any case to see if there is any impetus from their side. Once I understood why you have the top BCs I can go to the next step and see if we can make some adaptions to the setup.

Best,

Jousef

The issue I see is the dual velocity (flow rate) boundary condition on the extractor. You should almost always set a velocity inlet and a pressure outlet. If you change the Extractor_Outlet to Constant Pressure Outlet then everything will probably work correctly. The extractor flow rate will be controlled by the Extractor_Inlet.

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I did the simulation as indicated, an error appeared with no explenation. As follows:

I have here the final results of that simulation.

On the top i made a mistake, i want the air to enter the exhaust and then exit the other way.

Once again thank you all for the help.

It looks like you have this set up as a transient simulation. Did you mean to make a time dependant simulation or a steady state simulation? Steady State is what I believe you want.

Because this is transient, there is a time step for each solution. The time step has a maximum value based on the Courant number. In this case you have a Courant number of over 100 so the simulation wonâ€™t run. If you cut your time step down by more than two orders of magnitude it might run.

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