In a shell and tube heat exchanger having triangular pitch, the shell side equivalent diameter is given by

A. $$\frac{{4\left( {0.86{{\text{p}}^2} - \pi {{\text{d}}^2}/4} \right)}}{{\pi {\text{d}}}}$$

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

C. $$\frac{{4\left( {0.86{{\text{p}}^2} - \pi {{\text{d}}^2}} \right)}}{{\pi {\text{d}}}}$$

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

Answer: Option A