# Logarithmic mean temperature difference for heat transfer

1. May 22, 2016

### amrmohammed

1. The problem statement, all variables and given/known data
[Update: just realized that the LMTD is a temperature difference, so my question was not valid] :P

Calculate the logarithmic mean temperature difference (LMTD) to heat water flowing through a tube from 21 C (Ti) to 40 C (Te) if the tube has a fixed temperature of 45 C (Ts).
I should then calculate the length needed, which I can do. I am stuck with calculating the logarithmic mean temperature difference as I get a number that is less than the initial temperature of the water, which I know should be wrong!

2. Relevant equations
LMTD = (Ti - Te)/(ln[(Ts-Te)/(Ts-Ti)])

3. The attempt at a solution
For the given parameters:
LMTD = (21-40)/(ln[(45-40)/(45-21)]) = 12.1 C

Last edited: May 22, 2016
2. May 28, 2016