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.
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.
Flow arrangements
There is mainly two different flow arrangement in heat exchangers,
Counter Current flow:
See the image below
There is mainly two different flow arrangement in heat exchangers,
Counter Current flow:
See the image below
- Counter current flow arrangement
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
Co-current flow (Parallel flow):
See the image below
- Parallel flow arrangement
How do we calculate it?
The log mean temperature difference is normally calculated from the terminal temperature differences.
The log mean temperature difference is normally calculated from the terminal temperature differences.
For Counter current flow:
For Co-current flow
Reference:
D. Q. Kern, Process Heat Transfer, McGraw-Hill, International Edition, 1950
D. Q. Kern, Process Heat Transfer, McGraw-Hill, International Edition, 1950
Free LMTD Calculator
- Log mean temperature difference calculator
