I do not know anything about fluid dynamics but if I have a 2 inch hole in a wall can I not move more water through it using 2" square tube vs 2" pipe as there is more area. Why do we just use round pipe? Could someone explain this to me? Thank you very much. Eric

Yes, you can move more water through a square 2" tube (width D) than a circular 2" pipe (diameter D), based on mass flow rate (cross-sectional area comparison):

Square = w * w = D * D = 4

Circle = pi * r * r = pi * D * D / 4 = 3.14

Now consider moving a fixed mass flow rate through both tubes, i.e. make the cross-sectional areas equal:

Square surface area per unit length = 4w

Circle surface area per unit length = pi *2 * r

Square / Circle cross-section area = (w * w) / (pi * r * r) = 1 (equal area)

Where w = square width and r = circle radius

Square / Circle surface area = 2 / sqrt(pi) = 1.128

So for a given mass flow rate:

• square tube will use more material in its construction than a circular pipe per unit length, thus cost more
• square tube will require more energy to pump fluid through it than circular pipe per unit length - recognizing that skin friction (losses) are proportional to surface area.

Thank you very much, I really appreciate the answer. Eric

what is the specification of describing the tube and the pipe

Not only that, but square pipe would require soldering or welding together of the joints, while round pipe screws together, and, probably most importantly, apart. You can't screw square pipes together.