# Pipe with change of section

I'm a novice in mechanical engineering and I'm having some troubles to find a pipe that change from one section to other. In this case I want to connect a circle section to a rectangular section. I google it but only found the second Figure. Water is going to be used with a pump of 4 HP. The diameter of the circular part is $$d_{int}=90 mm.$$ and the dimensions of the rectangular side are less than the $$d_{int}$$. So basically, I want to know how to search them or are there any mechanism that can replace what I'm trying to do?

• I'm curious to know what this application is, I've never seen rectangular piping/tubing only rectangular ductwork for HVAC applications. – J. Ari Oct 15 '20 at 15:35