How to Calculate the Log Mean Temperature Difference (LMTD)
This short article aims to show you how to calculate the LMTD for Counter current flow and Co-current flow also called (Parallel flow). The calculation has been referenced by many text books. You can also download the free calculator attached with this article.
Why do we need to calculate it?
The log mean temperature difference represents the driving force for heat exchanger operation. It will allow us to make a decision on the flow arrangement type and making the right choice here will also improve your final design and mainly the heat transfer.
How do we calculate it?
The log mean temperature difference is normally calculated from the terminal temperature differences.
Flow arrangements
There is mainly two different flow arrangement in heat exchangers
| Counter Current flow | Parallel flow |
|---|---|
 |  |
For Counter flow
For Co-current flow
Where: T1 - Inlet temperature of hot stream T2 - Outlet temperature of hot stream t1 - Inlet temperature of cold stream t2 - Outlet temperature of cold stream
Reference
D. Q. Kern, Process Heat Transfer, McGraw-Hill, International Edition, 1950
Free LMTD Calculator
