The surface renewal frequency in Danckwerts model of mass transfer is given by (K_L: mass transfer co-efficient)

A. $$\sqrt {{{\text{K}}_{\text{L}}}^2 \cdot {{\text{D}}_{\text{A}}}} $$

B. $${{\text{K}}_{\text{L}}}^2 \cdot {{\text{D}}_{\text{A}}}$$

C. $$\frac{{{{\text{K}}_{\text{L}}}^2}}{{{{\text{D}}_{\text{A}}}}}$$

D. $$\frac{{{{\text{K}}_{\text{L}}}}}{{{{\text{D}}_{\text{A}}}^2}}$$

Answer: Option A