Why cross section of blast furnace is circular?

Answer 1

Hmmm ... That is the best way to build it.

A circle is the shape which encloses the maximum area for a given perimeter, so you would use less material for the wall.

If something has pressure from the inside, it will take the form of a circle. Similarly, when you blow up a balloon, it takes the shape of a sphere.

If the cross section were say, a square, the walls would bow out (unless they were very strong), and tend to make a circular shape.