The efficiency η f of a straight fin with a rectangular cross section is determined by measuring three temperatures: the temperature ϑ0 at the fin base, the temperature ϑ h at the top of the fin and...

The efficiency η_f
of a straight fin with a rectangular cross section is determined by measuring three temperatures: the temperature ϑ0 at the fin base, the temperature ϑ_h
at the top of the fin and the temperature ϑ_S
of the fluid which surrounds the fin. Calculate η_f
for ϑ₀
= 75.0 ◦C, ϑ_h
= 40.5 ◦C and ϑ_S
= 15.0 ◦C.