## 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