Yeah well I have built a few over the years & found that if you enter the water at a tangent, then the length of the reactor can be dramatically reduced but I also found that if the water is added fast enough a vortex will appear inside he reactor.
I still have a large stock of PVC fitting & found all the components I needed in my store, I have used 75mm clear PVC as the main tube for this one.
I have had it spinning in my outdoor test tank (old bath) & it gets a lovely vortex right down the whole length of the pipe but required a 60w pump to get it there!
Once a vortex is spinning nicely there will be a 100% dissolve rate, in fact I have built very short versions from 40mm pipe that worked extremely well with just a small powerhead.
I am really surprised there are not commercially made vortex units for sale, although you can buy those internal devices that are filled with bioballs & they can be converted easily.