"Venturi" or "Dyson" slit in extruder doesn't actually work
So after some time using the printer (25 days runtime) I've decided to disassemble the printer (Original Prusa I3 Mk3 R3) to do maintenance and upgrades.
And I noticed this:
And there is simply no dust in the slit. Evertything else, the fans, the aluminium heatsink fins, the whole inside surface of the extruder is covered in fine grey dust, but the inside if the slit is absolutely pristine and speckless. That can mean only one thing. There is no airflow through the slit. No air multiplication. It doesn't work.
And I'd be quite surprised if it did. The air from the Noctua fan doesn't have the speed required to create suction.
RE: "Venturi" or "Dyson" slit in extruder doesn't actually work
Indeed. This has been noted before - someone did an airflow analysis on it and found that air actually flows OUT of it. There have been alternative models (Butterworth Design) that do away with this slit entirely.
RE: "Venturi" or "Dyson" slit in extruder doesn't actually work
After the upgrades, I'm now on a full Bondtech geared extruder and that one has done away with the slit, too. Nevertheless I thought it'd be worth it sharing not just a mathematic simulation, but actual evidence that there is no air flowing there.
RE: "Venturi" or "Dyson" slit in extruder doesn't actually work
Not sure about you, but an airflow simulation and flow diagram is pretty good evidence a design doesn't work. I seem to recall Randolph-L did the analysis. And I tested using a match.
RE: "Venturi" or "Dyson" slit in extruder doesn't actually work
I guess I need to dig through the archives, as I'm discovering the already well confirmed. 🙂
And about me - I've got a physics background, so I consider a simulation a theory, a theory that one may even rely on, but still a theory that gets validated by an experiment or observation. Your flame test, of course, confirms it, too.
RE: "Venturi" or "Dyson" slit in extruder doesn't actually work
Well, independent confirmation of a theory is always good...
RE: "Venturi" or "Dyson" slit in extruder doesn't actually work
The problem with physicists is they generally study nothing that is tangible -- until it explodes.
RE: "Venturi" or "Dyson" slit in extruder doesn't actually work
My laser cutter has exploded a couple times already. The 3D printer is so far disappointingly quiet.
RE: "Venturi" or "Dyson" slit in extruder doesn't actually work
The printer will get there: after about 2000 hours and the bed can rotate a few degrees and perimeters begin looking more like woven bamboo and rattan; you'll order up the the Semtex to fix the problem.
RE: "Venturi" or "Dyson" slit in extruder doesn't actually work
Yeah, the venturi thing is a cool idea, but it doesn't do much in this application. My simulation did show some (negligible) flow inward, toward the heatsink, but flow from the venturi port would likely end up missing the heatsink entirely. At the end of the day, it doesn't really hurt anything, but I don't think it helps anything either.
MyMiniFactory (Functional Parts and Mods): https://www.myminifactory.com/users/butterworthdesign
Thingiverse (Fun Designs and Remixes): https://www.thingiverse.com/uscbutterworth/designs
Twitter: @USCbutterworth https://twitter.com/USCbutterworth