Could you explain why LMTD is introduced in a heat exchanger?

LMTD stands for Logarithmic Mean Temperature Difference and is formulated as,LMTD = {(∆T - ∆t) / ln(∆T/∆t)}, where ∆T and ∆t amount to the temperature difference between the fluids at both the ends of the Heat Exchanger. The temperature change that takes place across the Heat Exchanger is not linear - it is exponential. LMTD is also a parameter used to determine the heat transfer rate through the Heat Exchanger. As the LMTD increases, the heat transfer speeds up.