FloWorks - "Face xx is not laying on the boundary between the solid and the fluid reg

Charles Linquist · May 1, 2013, 11:05

I'm using FloWorks, and I'm new at it. I have an electronics enclosure that has a fan bolted to the inside of one of the cabinet walls - blowing outwards. I have set up everything and when I get to boundary conditions, I tell FloWorks that I want the volumetric flow rate of the air coming out of the fan. I highlight the fan flange that is attached to the cabinet wall, and when I press the check-box, I always get the msg.

"Face xxx is not laying on the boundary between the solid and the fluid regions"

Nothing I do will stop this message. What am I doing wrong?

Charles Linquist · May 2, 2013, 11:26

I'm attaching a picture of the enclosure in the hope that someone will help. Note that the top has been hidden.
The air enters the end opposite the fan, on both sides of the 'front panel'.

The air goes through the heatsink fins on both sides and eventually enters the chamber that houses the fan. There is NO airflow inside the enclosure, which is sealed.

I did not find an easy way to tell FloWorks to not consider the fact that there is no airflow inside the box.

Still, I think It should be able to figure that out.

Charles Linquist · May 2, 2013, 11:28

The fan you see is the outlet of the air.

Boris_M · May 6, 2013, 03:22

Hi Charles,

I think the problem you have lies within your model, not FloWorks. This message indicates that you might have an invalid contact. An invalid contact is a tangential contact which not defined for the numerical part of the software if there is fluid going through this invalid contact or not as there is no clear surface contact or overlapping of the two bodies in contact.
The way to find it is usually to use the "Check Geometry" feature. This should highlight you the problematic region/parts, depening on which FloWorks version you use. The easiest way is then to creat a simple overlap of these parts by just a tiny bit (0.01mm) which is enough get rid of the tangential contact and make it an overlapping contact. The software can handle such overlaps perfectly.

There are two other suggestions. If you don't want to calculate the fluid inside the enclosure then you can use the option "Exclude internal space" and "Exclude cavities without flow conditions". So if your internal space is sealed and therefore watertight, this volume is not used in the calculation.

The other suggestion is to use a fan curve as this is representing the actual fan behaviour and flow rate more accuratly than apply a constant flow rate. Except if you controll the flow rate in some way.

By the way, a nice model you have there :-)

Regards,
Boris

Charles Linquist · May 6, 2013, 10:59

Boris, Thanks for the input.

I am using a fan curve. My goal is to determine just how much air is going through the fins, and also just how much heat I can dissipate. I'll add a heat source next.

And, although I would like to take credit for the model, it was made by our resident SolidWorks expert - Jorge Hernandez.

May 1, 2013, 11:05	FloWorks - "Face xx is not laying on the boundary between the solid and the fluid reg	#1
Charles Linquist New Member Join Date: May 2013 Posts: 4 Rep Power: 12	I'm using FloWorks, and I'm new at it. I have an electronics enclosure that has a fan bolted to the inside of one of the cabinet walls - blowing outwards. I have set up everything and when I get to boundary conditions, I tell FloWorks that I want the volumetric flow rate of the air coming out of the fan. I highlight the fan flange that is attached to the cabinet wall, and when I press the check-box, I always get the msg. "Face xxx is not laying on the boundary between the solid and the fluid regions" Nothing I do will stop this message. What am I doing wrong?

May 2, 2013, 11:26	More information	#2
Charles Linquist New Member Join Date: May 2013 Posts: 4 Rep Power: 12	I'm attaching a picture of the enclosure in the hope that someone will help. Note that the top has been hidden. The air enters the end opposite the fan, on both sides of the 'front panel'. The air goes through the heatsink fins on both sides and eventually enters the chamber that houses the fan. There is NO airflow inside the enclosure, which is sealed. I did not find an easy way to tell FloWorks to not consider the fact that there is no airflow inside the box. Still, I think It should be able to figure that out.

May 2, 2013, 11:28	Another view	#3
Charles Linquist New Member Join Date: May 2013 Posts: 4 Rep Power: 12	The fan you see is the outlet of the air.

May 6, 2013, 03:22		#4
Boris_M Disabled Join Date: Jul 2009 Posts: 616 Rep Power: 23	Hi Charles, I think the problem you have lies within your model, not FloWorks. This message indicates that you might have an invalid contact. An invalid contact is a tangential contact which not defined for the numerical part of the software if there is fluid going through this invalid contact or not as there is no clear surface contact or overlapping of the two bodies in contact. The way to find it is usually to use the "Check Geometry" feature. This should highlight you the problematic region/parts, depening on which FloWorks version you use. The easiest way is then to creat a simple overlap of these parts by just a tiny bit (0.01mm) which is enough get rid of the tangential contact and make it an overlapping contact. The software can handle such overlaps perfectly. There are two other suggestions. If you don't want to calculate the fluid inside the enclosure then you can use the option "Exclude internal space" and "Exclude cavities without flow conditions". So if your internal space is sealed and therefore watertight, this volume is not used in the calculation. The other suggestion is to use a fan curve as this is representing the actual fan behaviour and flow rate more accuratly than apply a constant flow rate. Except if you controll the flow rate in some way. By the way, a nice model you have there :-) Regards, Boris

May 6, 2013, 10:59		#5
Charles Linquist New Member Join Date: May 2013 Posts: 4 Rep Power: 12	Boris, Thanks for the input. I am using a fan curve. My goal is to determine just how much air is going through the fins, and also just how much heat I can dissipate. I'll add a heat source next. And, although I would like to take credit for the model, it was made by our resident SolidWorks expert - Jorge Hernandez.