The efficiency of a pin fin with insulated tip is

• A. \(\frac{{tanhmL}}{{\sqrt {\frac{{hA}}{{kP}}} }}\)
• B. \(\frac{{tanhmL}}{{mL}}\)
• C. \(\frac{{mL}}{{tanhmL}}\)
• D. \(\frac{{\sqrt {\frac{{hA}}{{kP}}} }}{{tanhmL}}\)