The logarithmic mean temperature difference ( t_ m ) is given by (where t_1 and t_2 are temperature differences between the hot and cold fluids at entrance and exit)

Answer: Option A

The logarithmic mean temperature difference ($${\text{t}}_{\text{m}}$$) is given by $${\text{t}}_{\text{m}}=\frac{\Delta {\text{t}}_1-\Delta {\text{t}}_2}{{\log }_{\text{e}}\left(\frac{\Delta {\text{t}}_1}{\Delta {\text{t}}_2}\right)}$$
Where $$\Delta {\text{t}}_1$$ and $$\Delta {\text{t}}_2$$ are temperature differences between the hot and cold fluids at entrance and exit.