I was going to suggest the same solution as Doax but I did not read the hole topic he posted.
The way I would do it is use flex pipe for the bends to connect to the outlet and to the drier between them would be a rigid pipe with fins as seen in the link he posted.
To construct it get several short sections of pipe (easier to work with) heat them up in the oven and then spray them with
VHT Wrinkle Plus™ Coatings (I believe that krylon has the same stuff and calls it crackle). That will double the surface area by turning it from a smooth surface to a textured one this was tested on a supercharger for air temps and cool off time.
Do the same with the fins, just remember to leave the part that you will attach to the pipe unpainted. I would also make sure to make a tape line on the pipe so you will have metal to metal contact. You could weld the fins in place or use thermal past (for CPUs) and pop-rivet them in place.
When putting the pipes together make sure that the upper pipe goes over the lower pipe, and if the drier is gas instead of electric I would also make sure to seal any holes that were created in the pipe.