just paraphrase these in order:
1. Friction factor (f) is a dimensionless empirical factor. The friction factor that is used in the Darcy Weisbech equation depends on the Reynolds number (Re)nd the pipe roughness. It is used to determine pressure loss (“Summary”, 2012).
2. Aluminum pipe with roughness of 0.0013-0.0015 mm (Roughness of Pipes).
3. Schedule number means the pipe thickness (Milbury).
4. Pipe size refers to nominal size not the actual size. The actual outer diameter (OD) is larger than its nominal diameter (“Pipe Vs Tube.”).
5. Tubes come in different shapes such as cylindrical, and rectangular. Pipes always come in a circular shape; this shape help the pressure force to distribute evenly throughout the pipe (“Pipe & Tube Industrial Applications. What’s the Difference?: IA Academy”).