Áo nước (water jacket) cho ống 15mm

Print two of these with the flat side down on the print bed.

Drill through the holes on only one of them with a 4mm drill bit. Put 4x M4 bolts of 30-40mm thread length through from the drilled side (clearance holes) into the non-drilled side. Tighten fully to cut threads and then disassemble again. Depending on your printer tolerances you may need to tap the non-clearance hole side with an M4 tap.

After disassembling, paint the insides with acrylic paint of PU varnish or similar to waterproof.

Use screws to clamp tightly round your 15mm outer diameter pipe with a smear of silicone along the mating surface to act as a gasket.

You'll need jubilee clips or similar to hold the 1/2" hose onto the barbs.

Of course being made of plastic the whole thing is extremely temperature limited. If you get even near the softening temp of your filament (50C-ish for PLA) the whole thing will distort and fail. I'm using a peltier and this is on the chilled water side.