The extruder injector duct does not work as intended
The injector duct that was added to the extruder version 3 would, through the injector effect, draw in some extra cooling air to the Heat sink.
A simulation of the air flow shows that the injector channel does not work as intended. Instead of sucking in air, the simulation shows that air is instead forced out through the duct.
The air velocity from the fan is too low, and the heat sink builds up a resistance that prevents the injector action.
My suggestion is that the air duct be removed so that more air can pass through the heat sink. On my extruder I have now placed a piece of kapton tape over the duct opening.
The picture shows a section through the air duct of the extruder.
Bear MK3 with Bondtech extruder
Re: The extruder injector duct does not work as intended
Good info - did you do a match test to confirm the FACFIN sim is accurate??
ps: I just did, and you're sim appears accurate: nothing but turbulence in the side channel.
Re: The extruder injector duct does not work as intended
I could see same thing during my testing (and several members of the Bear community as well), thank you for having confirmed this with a very visual result! Great job as always!
I did test that with fume and with a hair that I stick to the hole entry. My testing were showing that in best case this hole is creating turbulence and worse case you are going to have both turbulence and air going out like your simulation. I tried both Sunon and Noctua and both have the same issue.
Another way to see that is to look at dust because it gets accumulated where there is turbulence. You should see plenty of dust in and around this hole if you open the cover.
Adding a tape on the hole will help a bit but will not solve the turbulence issue.