Update (V2.2)

I tested a bit around different smaller design changes and validated them ROUGHLY with CFD (I am not an Engineer or somebody who knows CFD very well). Picture of the rough CFD Simulation attached.
I made small changes like increasing the hole size of the arms/fangs as well as make them higher on the outside but not on the inside to hopefully keep clearance for V6 cables.
The air is now less restricted and flows more downwards. V2 Airflow was going nearly straight from both sides and thus going upwards when meeting in the middle.
This version needs to be Mounted a bit higher than V2 because of that.

Update (V2)

I redesigned the Arms completely. Now the air travels much more to the outside to come back to the nozzle in the straight way. The old design pushed the air out at 45° degree angle and was much higher which made problems with the wiring of V6 Heaterblocks. The "highClearance" version didn't seem to fully mitigate that and had other drawbacks.

Now with the new and flatter Arm design this should be fixed. Also now the air truly comes out at nearly 90° angle from both sides and meeting directly in the middle on the Nozzle for maximum part cooling Efficiency. It now should be even better at overhangs and bridging than the V1 version which already was extremely good at cooling the hot filament.
The Downside is that its now wider than Hemera so on some Printers it MIGHT need some Endpoint offsets. So pleases check carefully before starting your first print!
On Ender 5 Plus even with Volcano this Cooler however doesn't collide with anything.

If you have an Volcano, the V1 still works fine but V2 should have slightly better performance.

Update (HighClearance Test)

If you are using the normal V6 Hotend you might wan't to choose the _highClearance version, Its fangs are 8mm more apart leaving more place for cables. Also its 4mm shorter to compensate the new center of Airflow (air comes out pretty much 45°). Also you want to mount it some Millimeters higher.

Original Text

So after I made my own Universal Fan Duct for Titan Aero in Onshape I made an completely new one for Hemera in Fusion360 with all the things I have learned from the old design and it flaws.
This FanDuct with its Mount is very adjustable in the height and is compatible with V6 and Volcano!
And one very important "feature" is that it is completely compatible no matter what Hemera-Mount you use as long as the Hemera is orientated for the stepper motor on the right side. But if you have an Ender 5 (Plus) or other Creality printers, you might want to check out my rail sliding mount for the Hemera. :)

What you need:

• the 4 the square Nuts inserted in all 4 Holes on the Hemera
• 4x M3x8mm for attaching the FanDuct_Mount Part to the Hemera (DON'T USE LONGER THAN 8mm SCREWS FOR THIS!)
• 50x15 Radial Fan, I highly recommend a good one with 6000 RPM from Sunon! Cheap slower ones strongly decrease the cooling!
• 2x M4x20mm screws for the fan, 25mm should work too.

Printing:

• Use a material like PETG for the FanDuct Part, because PLA problably won't withstands the heat for long! The Fan Duct is not extremely close to the heaterblock so PLA will work for at least a time.
• I designed it with wall strengths of 1.6mm so that I can print it well with my 0.8mm nozzle. If you have an smaller nozzle there should not be a problem, .4 would be perfect too with double the perimeters.
• Both Parts don't need support to print, but use as much cooling as your current setup is able to. ;)

Installation:

• Both Parts already are rotated correctly for optimal printing
• Install the Mount
• Put the Fan in the Fan Duct and the Screws through it
• Important: Position the FanDuct so that the height-clearance between the underside to the nozzle tip is like 5-7 mm. You really want the airflow to go around and down the nozzle. Also you really want to use the silicone sock because of that.
• Also don't worry that it looks like the air slots of the FanDuct are misaligned way before the nozzle. The air will come out at a great angle so that it will hit the nozzle perfectly.
• Screw the M4 Screws into the long holes of the Mount (they will tape them self into the plastic)
• connect the fan correctly
• Optional: PID re-tune your Heater