The friction factor for laminar flow in round tubes is often taken to be:

He stood at the mouth of the new bore, a straight, round tube fifty feet across.

This was not a round tube.

The throat opened into a round tube, ready to eject the column of fire.

He had no names for them, but he recognized the difference between a round tube and a square tabletop.

Jorongmok is the round tube in the middle connecting the left and right side of the hourglass-shaped body.

And about three months later this thing came back, this little round tube, you know.

Profiling are for example used lot in the sensor, where a circuit need to fit round tubes or other different complex shapes.

Using this term one can calculate many things in the same way as for a round tube.

They were on a grid, and a ladder went down farther still, into a round tube.