Solve the below problem:
Q: Ethanol at 20°C flows at 125 U.S. gal/min through a horizontal cast-iron pipe with L = 12 m and d = 5 cm. Neglecting entrance effects, estimate
(a) the pressure gradient, dp/dx;
(b) The wall shear stress, tw; and
(c) the percent reduction in friction factor if the pipe walls are polished to a smooth surface.