- Whenever an industry needs to purchase or design a heat exchanger, there are several required tasks or parameters that should satisfy the industry standard like....
- For known mass flow rate, select the heat exchanger that will achieve a pre-defined temperature change in a fluid stream or…
- For a given or known size of the heat exchanger, determine the outlet temperature of the cold and hot fluid stream.
- To solve these two criteria, Engineers designed the heat exchanger and carried out an analysis of it. Generally, there are two methods of analysis and design of heat exchangers.
- Log mean temperature difference (LMTD)
- Effectiveness – NTU method
The LMTD method of analysis and design of the heat exchanger is best suited for the first task.
Log mean temperature difference (LMTD)
In the heat exchanger, the rate of heat transfer is calculated by,
U = Overall heat transfer coefficient
As= Surface area of tubes
dT = Temperature difference between cold and hot fluids
- Sometimes a situation arises when you need to design or order a heat exchanger according to fix space in which it can be installed properly without compromising the industry requirement like pre-determined (Already known) inlet temperature of hot fluid, the outlet temperature of cold fluid, and heat transfer rate Q.
- In this situation, the LMTD (Log mean temperature difference) method of analysis of the heat exchanger is used. In LMTD, the inlet temperature of hot fluid and both the inlet and outlet temperature of cold fluid are known. Also heat transfer rate Q and overall heat transfer coefficient U are known. Based on that parameters, you need to determine the size of the heat exchanger as the surface area can be calculated from the heat transfer rate equation.
- In short, LMTD (Log mean temperature difference) method is very suitable for identifying the size of the heat exchanger when the inlet temperature of the hot fluid and both the inlet and outlet temperature of the cold fluid and the mass flow rate are specified.
