Sorry I did not see the picture: Now everything is fine, I do not see what could belfry! I did not see the wall shown in the center that makes the connection between the round tube and square tube. I imagine that the passage of the round tube to square tube, used to create turbulence?
Answered with a tutorial: https://grabcad.com/tutorials/extrude-a-path-inside-a-sphere
Attachmentssphere avec tube interne.SLDPRT, 317 KB