Question

why do we use log mean temperature difference:quora

Answer 1

In a heat exchanger which passes two fluids - hot and cold, analysis of how much heat is transferred is done by LMTD .

LMTD or Log Mean Temperature Difference is an equivalent mean temperature difference between the two fluids for the entire heat exchanger.

From the figure below,

Let Th= Temperature difference between input and output of hot fluid= T(hi) -T (ho)

and Tc=Temperature difference between input and output of cold fluid= T(co) -T (ci)

The formula is given by :

LMTD = (Th−Tc)/ln(Th/Tc)