In a shell and tube heat exchanger having square pitch, the shell side equivalent diameter is given by (where, P = pitch, d = outside diameter of the tube)

A. $$\frac{{4\left( {{{\text{p}}^2} - \pi {{\text{d}}^2}/4} \right)}}{{\pi {\text{d}}}}$$

B. $$\frac{{{{\text{p}}^2} - \pi {{\text{d}}^2}/4}}{{\pi {\text{d}}}}$$

C. $$\frac{{4{{\text{p}}^2}}}{{\pi {\text{d}}}}$$

D. $$\frac{{\pi {\text{d}}}}{{4{{\text{p}}^2}}}$$

Answer: Option A