The loss of head due to viscosity for laminar flow in pipes is (where d = Diameter of pipe, $$l$$ = Length of pipe, v = Velocity of the liquid in the pipe, $$\mu $$ = Viscosity of the liquid and w = Specific weight of the flowing liquid)

A. $$\frac{{4\mu {\text{v}}l}}{{{\text{w}}{{\text{d}}^2}}}$$

B. $$\frac{{8\mu {\text{v}}l}}{{{\text{w}}{{\text{d}}^2}}}$$

C. $$\frac{{16\mu {\text{v}}l}}{{{\text{w}}{{\text{d}}^2}}}$$

D. $$\frac{{32\mu {\text{v}}l}}{{{\text{w}}{{\text{d}}^2}}}$$

Answer: Option D