Answer :

Corrrect answer is : 49.3

Given, T_hi = 102°C, T_he = 65°C

T_ci = 25°C, T_ce = 42°C

ΔT_i = T_hi – T_ce = 102 – 42 = 60°C

ΔT_e = T_he - T_ci = 65 – 25 = 40°C

Log mean temperature difference is given by

$L_{MTD}=\frac{\mathrm{\Delta }{T}_i-\mathrm{\Delta }{T}_e}{\ln \frac{\mathrm{\Delta }Ti}{\mathrm{\Delta }Te}}$

$\therefore LMTD=\frac{60-40}{\ln \left(\frac{60}{40}\right)}={49.3}^{\circ }C$