I am solving the following problem:
A liquid-to-liquid counterflow heat exchanger is used to heat a cold fluid from 120 °F to 310 °F. Assuming that the hot fluid enters at 500 °F and leaves at 400 °F, calculate the log mean temperature difference for the heat exchanger.
The given answer is 232 °F
I used:
$${ LMTD = \frac{\triangle max - \triangle min }{ ln( \frac {\triangle max}{\triangle min} ) } }$$
$${ \triangle max = 500-120 = 380 }$$ $${ \triangle min = 400-310= 90}$$
I plug them all together and I got 201.3383331.
What am I doing wrong?