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Bed Fan Duct

Posted: Sat Oct 08, 2016 6:20 pm
by quaver
In the process of updating to an E3Dv6 hot end. As this requires a new extruder mount I decided to try a duct for my 50mm bed fan. I have attached a few shots of the design. Thoughts/comments/suggestions? I am not convinced that a bed fan duct really helps cooling or improves print performance but it seems many users have adopted them. The duct improves containment of the airflow but it also causes a pressure drop which lowers mass flow. Perhaps a duct with a higher capacity fan (20mm thick vs 10mm) is better but it seems simply using the same fan with a duct could potential reduce printing performance.

Re: Bed Fan Duct

Posted: Sun Oct 09, 2016 6:06 am
by quaver
Finished the attachment design and fan guard. Mounting bar (green) is held to the extruder mount (brown) by two machine screws. Duct (blue) attached by means of a dove-tail tab. Should be easy and quick to install/remove. Fan guard is a new design intended to reduce noise level and improve airflow. I plan to use the E3D provided heat-break fan and shroud (not shown) oriented with the fan to the side or rear.

Re: Bed Fan Duct

Posted: Mon Oct 10, 2016 1:07 am
by insta
Very nice!

Make one for the V4 :mrgreen:

Re: Bed Fan Duct

Posted: Tue Oct 11, 2016 12:01 am
by quaver
Thanks Insta. For grins and giggles I ran a simple CFD analysis on the duct assuming a 0.1" H2O static pressure at the inlet. Distribution looks nice and it seems the tongue in the center nudges air to the perimeter on either side which is what I was hoping would occur. The simulation does not take turbulence from the fan into account so everything looks nice and uniform. I will likely add a .25" straightener in the section of the throat just below the flange face to help reduce turbulence.

Re: Bed Fan Duct

Posted: Wed Oct 12, 2016 4:14 am
by quaver
CFD of the fan guard looks promising as well. Very little pressure drop (<0.09" H2O) and good distribution. Knock off a few of the sharp, interior downstream edges and it should be in good shape.

Re: Bed Fan Duct

Posted: Wed Oct 12, 2016 5:20 am
by insta
Which is fantastic, but doesn't solve my v4 problem ;)

Re: Bed Fan Duct

Posted: Fri Oct 14, 2016 6:48 pm
by quaver
To beat a dead horse... I decided to run a CFD check on the whole bed fan system as an assembly. Interesting results. Found turbulence downstream of the fan motor support plate (see graphic). This structure is the same diameter as the hub of the fan. Gluing a simple cone to the back of this surface (yellow part in section view) solves this problem improving flow performance and likely reducing noise. Hope to build parts and test within the coming weeks.

It also looks like I will creating a version for the V4 for Insta... ;)

Re: Bed Fan Duct

Posted: Sat Oct 15, 2016 3:11 am
by zemlin
Nice looking rig, and interesting analysis. I'll try the cone thing on my duct setup.

Re: Bed Fan Duct

Posted: Sat Oct 15, 2016 4:03 am
by insta
quaver wrote:It also looks like I will creating a version for the V4 for Insta... ;)
I will trade you a PEI MIC6 bed for a 50mm fan duct STL that fits my setup and can be printed without much in the way of supports.

Re: Bed Fan Duct

Posted: Sat Oct 15, 2016 5:43 am
by kartcrg
insta wrote:
quaver wrote:It also looks like I will creating a version for the V4 for Insta... ;)
I will trade you a PEI MIC6 bed for a 50mm fan duct STL that fits my setup and can be printed without much in the way of supports.
If he doesn't take you up on that, I will ;)
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