Vortex micro-spray head for 6.5 mm (1/4 inch) OD pipe.

The design uses two conical surfaces to obtain internal volumes, but obviating the use of internal support. The spray head prints surprisingly well (at least on my stock standard MK3S+).

The first (top) cavity, between the two cones, spreads the water from the supply nozzle into four vertical pipes located in the corners of the device. The circular vortex (lower) cavity is fed along the perimeter from the four corners, with the water from the four pipes bent degrees into the horizontal plane. There are four feeds to achieve sufficient flow and overcome poor printing issues.

There are four versions of the head, using 1, 2, 3, or 4 of the pipes, to achieve different flow rates. The number of pipes is cut into the base. I printed all four types, but only really tested the 4-version.

Use 90% infill, but the exact value should not make much of a difference, the spray head has 2 or 3 perimeters with practically no 'infill' volume.

Under really high pressure the head may leak between printing layers, ejecting minute jets of water. This is not an issue, because the volume of water lost is small, and it adds to the spray :-)

Test each head by blowing through it before mounting to ensure that it is not blocked.  There is no rework or cleaning possible, the inner shapes are too intricate and enclosed to try and fix. Out of 15 printed nozzles I had no failures all worked fine.

Micro-sprayer piping ID 4 mm,  OD 6.5 mm (1/4 inch).
Micro-sprayer head 10x10 mm
Nozzle: 
        pipe ID 2.5, two outer diameters OD 5.3 (rear) & 4.5 (front)
        flange OD 6.5 mm, length to flange 5
        total length 10 mm

Slicing (PrusaSlicer):

Printed in PETG, but any material should work.
Layer height 0.2 mm, Quality settings
Vertical perimeters: 2
Horizontal top/bottom layers: 5/4
Perimeter generator: Arachne
Infill 90% gyroid - not really relevant because there is only perimeter.
Support: None

I use these sprayers with the spikes available here https://www.printables.com/model/733551